Decoding Ca2+ signals: a question of timing

Receptor-stimulated Ca2+ signals come in several flavors. The Ca2+ signals can be decoded linearly or by integration of the response. How the duration of the signal conveyed by cytosolic Ca2+ concentration ([Ca2+]i) changes is regulated is not well understood. Liu et al. (Liu, Q., S.A. Walker, D. Gao, J.A. Taylor, Y.-F. Dai, R.S. Arkell, M.D. Bootman, H.L. Roderick, P.J. Cullen, and P.J. Lockyer. 2005. J. Cell Biol. 170:183–190) now report an example of decoding based on the differential regulation of Ras function by two Ca2+-sensitive Ras inhibitors: Ca2+-promoted Ras activator (CAPRI), which extends the duration of the effect of Ca2+ on Ras activity, and Ras GTPase activating-like protein (RASAL), which functions as a linear decoder of the Ca2+ signal

Transient receptor potential canonical type 3 channels control the vascular contractility of mouse mesenteric arteries

Transient receptor potential canonical type 3 (TRPC3) channels are non-selective cation channels and regulate intracellular Ca2+ concentration. We examined the role of TRPC3 channels in agonist-, membrane depolarization (high K+)-, and mechanical (pressure)-induced vasoconstriction and vasorelaxation in mouse mesenteric arteries. Vasoconstriction and vasorelaxation of endothelial cells intact mesenteric arteries were measured in TRPC3 wild-type (WT) and knockout (KO) mice. Calcium concentration ([Ca2+]) was measured in isolated arteries from TRPC3 WT and KO mice as well as in the mouse endothelial cell line bEnd.3. Nitric oxide (NO) production and nitrate/nitrite concentrations were also measured in TRPC3 WT and KO mice. Phenylephrine-induced vasoconstriction was reduced in TRPC3 KO mice when compared to that of WT mice, but neither high K+- nor pressure-induced vasoconstriction was altered in TRPC3 KO mice. Acetylcholine-induced vasorelaxation was inhibited in TRPC3 KO mice and by the selective TRPC3 blocker pyrazole-3. Acetylcholine blocked the phenylephrine-induced increase in Ca2+ ratio and then relaxation in TRPC3 WT mice but had little effect on those outcomes in KO mice. Acetylcholine evoked a Ca2+ increase in endothelial cells, which was inhibited by pyrazole-3. Acetylcholine induced increased NO release in TRPC3 WT mice, but not in KO mice. Acetylcholine also increased the nitrate/nitrite concentration in TRPC3 WT mice, but not in KO mice. The present study directly demonstrated that the TRPC3 channel is involved in agonist-induced vasoconstriction and plays important role in NO-mediated vasorelaxation of intact mesenteric arteries.Fil: Yeon, Soo-In. Yonsei University College of Medicine; Corea del SurFil: Kim, Joo Young. Yonsei University College Of Medicine; . Yonsei University College of Medicine; Corea del SurFil: Yeon, Dong-Soo. Kwandong University College of Medicine; Corea del SurFil: Abramowitz, Joel. National Institute of Environmental Health Sciences; Estados UnidosFil: Birnbaumer, Lutz. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. National Institute of Environmental Health Sciences; Estados UnidosFil: Muallem, Shmuel. National Institutes of Health; Estados UnidosFil: Lee, Young-Ho. Yonsei University College of Medicine; Corea del Su

Israeli pediatricians’ confidence level in diagnosing and treating children with skin disorders: a cross-sectional questionnaire pilot study

BackgroundPediatricians daily see large numbers of patients with skin disorders. However, they encounter limited guidance as a result of a marked deficiency in pediatric dermatologists. Hence, reevaluation of training opportunities during pediatric residency has become essential. Our aim was to evaluate the confidence level of pediatric residents and specialists in diagnosing and treating skin disorders in children and to determine career and training-related characteristics that influence it.MethodsConducted as a cross-sectional study, we administered a questionnaire to 171 pediatricians across Israel. We assessed respondents’ self-efficacy about their ability to diagnose and treat skin disorders and collected data regarding their previous dermatology training and preferred training methods.Results77.8% of respondents reported below or average self-efficacy scores in diagnosing and managing children with skin disorders. Older age (>40 years old; OR = 5.51, p = 0.019), treating a higher number of patients with skin disorders (OR = 2.96, p = 0.032), and having any training in dermatology, either during medical school or residency (OR = 7.16, p = 0.031, OR = 11.14, p = 0.003 respectively), were all significant parameters involved in pediatricians reporting high self-efficacy in skin disorder management.ConclusionMost pediatric residents and pediatricians have average or below-average confidence in managing pediatric skin disorders. We suggest incorporating dermatology rotations during pediatric residency to improve young pediatricians’ self-efficacy in managing skin disorders and ultimately help pediatricians provide better care for patients presenting with dermatological conditions. These findings can ultimately help refine a pilot program in dermatology that might be implemented during pediatric residency

Coupling Modes and Stoichiometry of Cl−/HCO3− Exchange by slc26a3 and slc26a6

The SLC26 transporters are a family of mostly luminal Cl− and HCO3− transporters. The transport mechanism and the Cl−/HCO3− stoichiometry are not known for any member of the family. To address these questions, we simultaneously measured the HCO3− and Cl− fluxes and the current or membrane potential of slc26a3 and slc26a6 expressed in Xenopus laevis oocytes and the current of the transporters expressed in human embryonic kidney 293 cells. slc26a3 mediates a coupled 2Cl−/1HCO3− exchanger. The membrane potential modulated the apparent affinity for extracellular Cl− of Cl−/HCO3− exchange by slc26a3. Interestingly, the replacement of Cl− with NO3− or SCN− uncoupled the transport, with large NO3− and SCN− currents and low HCO3− transport. An apparent uncoupled current was also developed during the incubation of slc26a3-expressing oocytes in HCO3−-buffered Cl−-free media. These findings were used to develop a turnover cycle for Cl− and HCO3− transport by slc26a3. Cl− and HCO3− flux measurements revealed that slc26a6 mediates a 1Cl−/2HCO3− exchange. Accordingly, holding the membrane potential at 40 and −100 mV accelerated and inhibited, respectively, Cl−-mediated HCO3− influx, and holding the membrane potential at −100 mV increased HCO3−-mediated Cl− influx. These findings indicate that slc26a6 functions as a coupled 1Cl−/2HCO3− exchanger. The significance of isoform-specific Cl− and HCO3− transport stoichiometry by slc26a3 and slc26a6 is discussed in the context of diseases of epithelial Cl− absorption and HCO3− secretion

Homer 2 tunes G protein–coupled receptors stimulus intensity by regulating RGS proteins and PLCβ GAP activities

Homers are scaffolding proteins that bind G protein–coupled receptors (GPCRs), inositol 1,4,5-triphosphate (IP3) receptors (IP3Rs), ryanodine receptors, and TRP channels. However, their role in Ca2+ signaling in vivo is not known. Characterization of Ca2+ signaling in pancreatic acinar cells from Homer2−/− and Homer3−/− mice showed that Homer 3 has no discernible role in Ca2+ signaling in these cells. In contrast, we found that Homer 2 tunes intensity of Ca2+ signaling by GPCRs to regulate the frequency of [Ca2+]i oscillations. Thus, deletion of Homer 2 increased stimulus intensity by increasing the potency for agonists acting on various GPCRs to activate PLCβ and evoke Ca2+ release and oscillations. This was not due to aberrant localization of IP3Rs in cellular microdomains or IP3R channel activity. Rather, deletion of Homer 2 reduced the effectiveness of exogenous regulators of G proteins signaling proteins (RGS) to inhibit Ca2+ signaling in vivo. Moreover, Homer 2 preferentially bound to PLCβ in pancreatic acini and brain extracts and stimulated GAP activity of RGS4 and of PLCβ in an in vitro reconstitution system, with minimal effect on PLCβ-mediated PIP2 hydrolysis. These findings describe a novel, unexpected function of Homer proteins, demonstrate that RGS proteins and PLCβ GAP activities are regulated functions, and provide a molecular mechanism for tuning signal intensity generated by GPCRs and, thus, the characteristics of [Ca2+]i oscillations

Aquaporin 1 water channel is overexpressed in the plasma membranes of pancreatic ducts in patients with autoimmune pancreatitis

Chronic pancreatitis with all kinds of etiologies is characterized by pancreatic exocrine dysfunction especially impaired fluid secretion from pancreatic ducts. However, the molecular mechanism of this impaired fluid secretion in chronic pancreatitis is largely unknown. Aquaporin water channels are intrinsic membrane proteins expressed most of the cell types which have high osmotic water permeability. Among them aquaporin 1 (AQP1) is a predominant water channel expressed in the plasma membranes of human pancreatic ducts. Exocrine function test revealed that fluid secretion was severely impaired in AIP. immunohistochemical analysis revealed that AQP1 is localized mainly in the apical and lateral membranes of small pancreatic ducts in control subjects. AQP1 expression was significantly increased in plasma membranes of pancreatic ducts in AIP. Upregulation of AQP1 expression seen in pancreatic ducts of patient with AIP may be caused by the reduced fluid secretion from the pancreas as compensation. Further study would be required to elucidate the precise molecular mechanism for the role of AQP1 in pancreatic fluid secretion from the pancreas in diseases characterized by the impaired ductal fluid secretion such as cystic fibrosis