TRPV4 Contributes to Resting Membrane Potential in Retinal Müller Cells: Implications in Cell Volume Regulation

Neural activity alters osmotic gradients favoring cell swelling in retinal Müller cells. This swelling is followed by a regulatory volume decrease (RVD), partially mediated by an efflux of KCl and water. The transient receptor potential channel 4 (TRPV4), a nonselective calcium channel, has been proposed as a candidate for mediating intracellular Ca2+ elevation induced by swelling. We previously demonstrated in a human Müller cell line (MIO-M1) that RVD strongly depends on ion channel activation and, consequently, on membrane potential (Vm ). The aim of this study was to investigate if Ca2+ influx via TRPV4 contributes to RVD by modifying intracellular Ca2+ concentration and/or modulating Vm in MIO-M1 cells. Cell volume, intracellular Ca2+ levels, and Vm changes were evaluated using fluorescent probes. Results showed that MIO-M1 cells express functional TRPV4 which determines the resting Vmassociated with K+ channels. Swelling-induced increases in Ca2+ levels was due to both Ca2+ release from intracellular stores and Ca2+ influx by a pathway alternative to TRPV4. TRPV4 blockage affected swelling-induced biphasic response (depolarization-repolarization), suggesting its participation in modulating Vm changes during RVD. Agonist stimulation of Ca2+ influx via TRPV4 activated K+ channels hyperpolarizing Vm and accelerating RVD. We propose that TRPV4 forms a signaling complex with Ca2+ and/or voltage-dependent K+ channels to define resting Vm and Vm changes during RVD. TRPV4 involvement in RVD depends on the type of stimuli and/or degree of channel activation, leading to a maximum RVD response when Ca2+ influx overcomes a threshold and activates further signaling pathways in cell volume regulation.Fil: Netti, Vanina Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Fernández, Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Kalstein, Maia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Pizzoni, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Di Giusto, Gisela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Rivarola, Valeria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Ford, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Capurro, Claudia Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; Argentin

Aquaporin-4 facilitates cell proliferation in retinal müller cells: implications in neuromyelitis optica

Müller cells are involved in controlling extracellular homeostasis in the retina, regulating cell swelling by a regulatory volume decrease (RVD) mechanism that depends on the efflux of solutes and water through Aquaporin-4 (AQP4). Müller cells are also important for retinal integrity, as they respond to injury by re-entering the cell cycle for tissue repair. Since AQP4 was reported to modulate cell volume during cell cycle progression and facilitate proliferation in astrocytes, the aim of this study was to evaluate, using the novel inhibitor TGN-020, if AQP4 was involved in human Müller cells? proliferation in physiological conditions. Considering that AQP4 is the target of autoantibody IgG-NMO present in the sera of patients with Neuromyelitis Optica (NMO), we also evaluated if cell proliferation was altered in the presence of IgG-NMO. MIO-M1 human Müller cells were exposed to 100 nM TNG-020 or vehicle or to 1/50 dilution of IgG-NMO positive or control sera. Cell volume (videomicroscopy) and cell proliferation (cell count, cell cycle analysis by flow cytometry and BrdU incorporation by immunofluorescence) were measured. AQP4 inhibition with TGN-020 reduced osmotic water permeability (Pf, µm/s) from 20.3±1.2 to 12.2±0.4 (n=5, p<0.001) and %RVD 15min from 54±4 to 17±3 (n=5, p<0.001). MIO-M1 cell proliferation was decreased by TGN-020 (doubling time in hours, control vs. TGN-020: 31±1 vs. 40±3, n=4, p<0.05) without affecting cell viability. TGN-020 also increased the % of cells in G1/G0 phase, decreased the S phase of cell cycle and reduced BrdU incorporation by 20%. IgG-NMO positive sera decreased AQP4 plasma membrane expression in MIO-M1 cells, reducing Pf from 22.4±1.5 to 15.9±0.6 µm/s (n=6, p<0.001) and %RVD 15min from 66±5 to 48±4 (n=6, p<0.005), as well as cell proliferation (doubling time in hours, control vs. IgG-NMO: 59±5 vs. 86±4, n=3, p<0.05) in comparison to control sera. We propose that inhibition or removal of AQP4 from the plasma membrane reduces AQP4-mediated water permeability altering cell proliferation. This is of particular importance in NMO, as the decreased ability of Müller cells to proliferate may affect retinal tissue repair.Fil: Netti, Vanina Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: White, Alan. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Di Giusto, Gisela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Fernández, Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Ford, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Echevarría, Miriam. Universidad de Sevilla; EspañaFil: Capurro, Claudia Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaReunión Anual de la Sociedad Argentina de FisiologíaRosarioArgentinaSociedad Argentina de Fisiologi

Metabolic Imbalance Effect on Retinal Müller Glial Cells Reprogramming Capacity: Involvement of Histone Deacetylase SIRT6

Retinal Müller glial cells (MGs) are among the first to demonstrate metabolic changes during retinal disease and are a potential source of regenerative cells. In response to a harmful stimulus, they can dedifferentiate acquiring neural stem cells properties, proliferate and migrate to the damaged retinal layer and differentiate into lost neurons. However, it is not yet known how this reprogramming process is regulated in mammals. Since glucose and oxygen are important regulatory elements that may help directing stem cell fate, we aimed to study the effect of glucose variations and oxidative stress in Müller cells reprogramming capacity and analyze the participation the histone deacetylase SIRT6, as an epigenetic modulator of this process. We found that the combination of high glucose and oxidative stress induced a decrease in the levels of the marker glutamine synthetase, and an increase in the migration capacity of the cells suggesting that these experimental conditions could induce some degree of dedifferentiation and favor the migration ability. High glucose induced an increase in the levels of the pluripotent factor SOX9 and a decrease in SIRT6 levels accompanied by the increase in the acetylation levels of H3K9. Inhibiting SIRT6 expression by siRNA rendered an increase in SOX9 levels. We also determined SOX9 levels in retinas from mice with a conditional deletion of SIRT6 in the CNS. To further understand the mechanisms that regulate MGs response under metabolic impaired conditions, we evaluated the gene expression profile and performed Gene Ontology enrichment analysis of Müller cells from a murine model of Diabetes. We found several differentially expressed genes and observed that the transcriptomic change involved the enrichment of genes associated with glucose metabolism, cell migration, development and pluripotency. We found that many functional categories affected in cells of diabetic animals were directly related to SIRT6 function. Transcription factors enrichment analysis allowed us to predict several factors, including SOX9, that may be involved in the modulation of the differential expression program observed in diabetic MGs. Our results underline the heterogeneity of Müller cells response and the challenge that the study of metabolic impairment in vivo represents.Fil: Sanhueza Salas, L. Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Centro de Estudios Farmacológicos y Botánicos. Universidad de Buenos Aires. Facultad de Medicina. Centro de Estudios Farmacológicos y Botánicos; ArgentinaFil: García Venzor, Alfredo. Ben Gurion University of the Negev; IsraelFil: Beltramone, Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Capurro, Claudia Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Toiber, Debra. Ben Gurion University of the Negev; IsraelFil: Silberman, Dafne Magalí. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Centro de Estudios Farmacológicos y Botánicos. Universidad de Buenos Aires. Facultad de Medicina. Centro de Estudios Farmacológicos y Botánicos; Argentin

Uroguanylin regulates net fluid secretion via the NHE2 isoform of the Na+/H+ exchanger in an intestinal cellular model

Uroguanylin (UGN) has been proposed as a key regulator of salt and water intestinal transport. Uroguanylin (UGN) activates cell-surface guanylate cyclase C receptor (GC-C) and modulates cellular function via cyclic GMP (cGMP), thus increasing electrolyte and net water secretion. It has been suggested that the action of UGN could involve the Na+/H+ exchanger, but the actual contribution of this transporter still remains unclear. The objective of our study was to investigate the putative effects of UGN on some members of the Na+/H+ exchanger (NHE) family, as well as to clarify its consequences on transepithelial fluid flow in T84 cells. In order to do so, transepithelial fluid flow (Jv) was studied by optic techniques and intracellular pH (pHi) was measured with a fluorescence method. Results showed that NHE2 is found at the apical membrane and has a major role in Na+ absorption; NHE1 and NHE4 are localized at the basolateral membrane with a house-keeping role in steady state pHi. Cell exposure to apical UGN increases net secretory Jv, without changing short-circuit currents nor transepithelial resistance, and reduces NHE2 activity. Therefore, at physiological pH, the effect on net Jv was produced mainly by a reduction in normal Na+ absorption through NHE2, rather than by the stimulation of electrolyte secretion. Our study shows that the effect of UGN on pHi is GC-C/cGMP-mediated and enhanced by sildenafil, thus involving PDE5 enzyme. Additionally, cell exposure to apical UGN results in intracellular alkalinization, probably due to indirect effects on basolateral NHE1 and NHE4, which have a major role in pHi regulation.Fil: Toriano, Roxana Mabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; ArgentinaFil: Ozu, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; ArgentinaFil: Politi, María T.. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; ArgentinaFil: Dorr, Ricardo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; ArgentinaFil: Curto, Maria de Los Angeles. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Capurro, Claudia Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; Argentin

Uroguanylin regulates net fluid secretion via the NHE2 isoform of the Na+/H+ exchanger in an intestinal cellular model

Uroguanylin (UGN) has been proposed as a key regulator of salt and water intestinal transport. Uroguanylin (UGN) activates cell-surface guanylate cyclase C receptor (GC-C) and modulates cellular function via cyclic GMP (cGMP), thus increasing electrolyte and net water secretion. It has been suggested that the action of UGN could involve the Na+/H+ exchanger, but the actual contribution of this transporter still remains unclear. The objective of our study was to investigate the putative effects of UGN on some members of the Na+/H+ exchanger (NHE) family, as well as to clarify its consequences on transepithelial fluid flow in T84 cells. In order to do so, transepithelial fluid flow (Jv) was studied by optic techniques and intracellular pH (pHi) was measured with a fluorescence method. Results showed that NHE2 is found at the apical membrane and has a major role in Na+ absorption; NHE1 and NHE4 are localized at the basolateral membrane with a house-keeping role in steady state pHi. Cell exposure to apical UGN increases net secretory Jv, without changing short-circuit currents nor transepithelial resistance, and reduces NHE2 activity. Therefore, at physiological pH, the effect on net Jv was produced mainly by a reduction in normal Na+ absorption through NHE2, rather than by the stimulation of electrolyte secretion. Our study shows that the effect of UGN on pHi is GC-C/cGMP-mediated and enhanced by sildenafil, thus involving PDE5 enzyme. Additionally, cell exposure to apical UGN results in intracellular alkalinization, probably due to indirect effects on basolateral NHE1 and NHE4, which have a major role in pHi regulation.Fil: Toriano, Roxana Mabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; ArgentinaFil: Ozu, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; ArgentinaFil: Politi, María T.. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; ArgentinaFil: Dorr, Ricardo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; ArgentinaFil: Curto, Maria de Los Angeles. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Capurro, Claudia Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; Argentin

Parameter estimation to study the immediate impact of aortic cross-clamping using reduced order models

Aortic cross-clamping is a common strategy during vascular surgery, however, its instantaneous impact on hemodynamics is unknown. We, therefore, developed two numerical models to estimate the immediate impact of aortic clamping on the vascular properties. To assess the validity of the models, we recorded continuous invasive pressure signals during abdominal aneurysm repair surgery, immediately before and after clamping. The first model is a zero-dimensional (0D) three-element Windkessel model, which we coupled to a gradient-based parameter estimation algorithm to identify patient-specific parameters such as vascular resistance and compliance. We found a 10% increase in the total resistance and a 20% decrease in the total compliance after clamping. The second model is a nine-artery network corresponding to an average human body in which we solved the one-dimensional (1D) blood flow equations. With a similar parameter estimation method and using the results from the 0D model, we identified the resistance boundary conditions of the 1D network. Determining the patient-specific total resistance and the distribution of peripheral resistances through the parameter estimation process was sufficient for the 1D model to accurately reproduce the impact of clamping on the pressure waveform. Both models gave an accurate description of the pressure wave and had a high correlation (R2 >.95) with experimental blood pressure data.Fil: Ventre, Jeanne. Centre National de la Recherche Scientifique; FranciaFil: Politi, Teresa. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Fernández, Juan M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Ghigo, Arthur R.. Université de Toulouse; FranciaFil: Gaudric, Julien. Centre National de la Recherche Scientifique; Francia. Université de Toulouse; FranciaFil: Wray, Sandra. Universidad Favaloro; ArgentinaFil: Lagaert, Jean Baptiste. Université Paris Sud; FranciaFil: Armentano, Ricardo Luis. Universidad de la República; UruguayFil: Capurro, Claudia Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Fullana, José Maria. Centre National de la Recherche Scientifique; FranciaFil: Lagrée, Pierre Yves. Centre National de la Recherche Scientifique; Franci

Cell Volume Regulation and Aquaporins

In the recent years, the importance of the volume of a given cell has been accepted not only in defining its intracellular osmolality and its shape, but also in defining other cellular functions, such as transepithelial transport, cell migration, cell growth, cell death and the regulation of intracellular metabolism (35). Since most cells have to perform these physiological functions under a variable osmotic stress, cell volume must be carefully regulated. Based on the origin of the disturbance, cell volume changes are frequently classified into two categories: anisosmotic (alterations in extracellular solute concentration) and isosmotic (alterations in intracellular solute concentration) volume changes. Because of the relatively high permeability of the plasma membrane for water, any such gradient results in the immediate flow of water into or out of the cell causing cell swelling or shrinkage. To regulate cell volume, cells use channels and transport systems to flux osmolytes across the plasma membrane, followed by the obligatory movement of water. The current review reflects these developments and focuses on the contributions of aquaporins water channels in regulatory volume processes in a variety of cells.Fil: Capurro, Claudia Graciela. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; ArgentinaFil: Galicia, Luciano. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; ArgentinaFil: Ford, Paula. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; Argentin

TRPV4 mediates flow-induced increases in intracellular Ca in medullary thick ascending limbs

Medullary thick ascending limbs (mTAL) regulate Na balance and therefore blood pressure. We previously showed that cell swelling and luminal flow activates the mechanosensitive channel TRPV4 in mTAL. AIM: We hypothesized that TRPV4 mediates flow-induced increases in intracellular Ca (Cai) in rat mTALs. METHODS: We performed ratiometric measurements of Cai in perfused mTALs. RESULTS: Increasing luminal flow from 0 to 20 nL min−1 caused Cai to peak 231 ± 29 nmol L−1 above basal concentrations (n = 18). The general TRPV inhibitor ruthenium red at 15 and 50 μmol L−1 reduced peak Cai by 41 ± 9 (P < 0.01; n = 5) and 77 ± 10% (P < 0.02; n = 6). The selective TRPV4 inhibitor RN1734 at 10 and 50 μmol L−1 reduced peak Cai by 46 ± 11 (P < 0.01; n = 7) and 76 ± 5% (P < 0.02; n = 5) respectively. To specifically target TRPV4, mTALs were transduced with adenoviruses expressing TRPV4 small hairpin (sh) RNA. In non-transduced control mTALs, luminal flow generated a peak increase in Cai of 111 ± 21 nmol L−1 (n = 8). In TRPV4shRNA-transduced mTALs, the Cai peak was reduced to 56 ± 8 nmol L−1 (P < 0.03, n = 9). Removing extracellular Ca completely abolished flow-induced increases in Cai. Increasing luminal flow in the presence of hexokinase 20 (U mL−1) to scavenge extracellular ATP did not modify significantly the increases in Cai induced by luminal flow. Finally, we studied the effect of the TRPV4 selective agonist GSK1016790A on Cai. In the absence of luminal flow, GSK1016790A (10 nmol L−1) increased Cai from 60 ± 11 nmol L−1 to 262 ± 71 nmol L−1 (P < 0.05; n = 7). CONCLUSION: We conclude that flow-induced increases in Cai are mediated primarily by TRPV4 in the rat mTAL.Fil: Cabral, Pablo D.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay; Argentina. Case Western Reserve University; Estados Unidos. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas; ArgentinaFil: Capurro, Claudia Graciela. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Garvin, Jeffrey L.. Case Western Reserve University; Estados Unido

Selective Cre-mediated gene deletion identifies connexin 43 as the main connexin channel supporting olfactory ensheathing cell networks

Many functions of glial cells depend on the formation of selective glial networks mediated by gap junctions formed by members of the connexin family. Olfactory ensheathing cells (OECs) are specialized glia associated with olfactory sensory neuron axons. Like other glia, they form selective networks, however, the connexins that support OEC connectivity in vivo have not been identified. We used an in vivo mouse model to selectively delete candidate connexin genes with temporal control from OECs and address the physiological consequences. Using this model, we effectively abolished the expression of connexin 43 (Cx43) in OECs in both juvenile and adult mice. Cx43-deleted OECs exhibited features consistent with the loss of gap junctions including reduced membrane conductance, largely reduced sensitivity to the gap junction blocker meclofenamic acid and loss of dye coupling. This indicates that Cx43, a typically astrocytic connexin, is the main connexin forming functional channels in OECs. Despite these changes in functional properties, the deletion of Cx43 deletion did not alter the density of OECs. The strategy used here may prove useful to delete other candidate genes to better understand the functional roles of OECs in vivo.Fil: Piantanida, Ana Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Acosta, Luis Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Brocardo, Lucila. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Capurro, Claudia Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Greer, Charles A.. University of Yale; Estados UnidosFil: Rela, Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; Argentin

Asymmetry in osmotic response of cortical collecting duct cells: Role of Aquaporin-2

Transition from antidiuresis to diuresis exposes cortical collecting duct cells (CCD) to asymmetrical changes in environment osmolality, inducing an osmotic stress, which activates numerous membrane-associated events. The aim of the present work was to investigate, either in the presence or not of AQP2, the transepithelial osmotic water permeability (Posm) following cell exposure to asymmetrical hyper- or hypotonic gradients. For this purpose, transepithelial net volume fluxes were recorded every minute in two CCD cell lines: one not expressing AQPs (WT-RCCD1) and another stably transfected with AQP2 (AQP2-RCCD1). Our results demonstrated that the rate of osmosis produced by a given hypotonic shock depends on the gradient direction (osmotic rectification) only in the presence of apical AQP2. In contrast, hypertonic shocks elicit Posm rectification independently of AQP2 expression, and this phenomenon may be linked to modulation of basolateral membrane permeability. No asymmetry in transepithelial resistance was observed under hypo- or hypertonicity, indicating that rectification cannot be attributed to a shunt through the tight junction path. We conclude that osmotic rectification may be explained in terms of dynamical changes in membrane permeability probably due to activation/ incorporation of AQPs or transporters to the plasma membrane via some mechanism triggered by osmolality.Fil: Chara, Osvaldo. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; ArgentinaFil: Ford, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; ArgentinaFil: Rivarola, V.. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas; ArgentinaFil: Parisi, Mario Nestor. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; ArgentinaFil: Capurro, Claudia Graciela. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; Argentin