Ion channel control of phasic insulin secretion.

Glucose-stimulated insulin secretion exhibits a biphasic pattern. The mechanism underling biphasic insulin secretion is not fully understood, but consensus exists that an elevation in [Ca2+]i is required for both first- and second-phase insulin secretion. The molecular identity of the pancreatic β-cell L-type Ca2+ channel has not been established and it has variably been reported to be CaV1.2 (α1C) or CaV1.3 (α1D). Though the cellular background to the two phases of release remains unknown, it has been suggested to reflect the sequential release of distinct pools of granules, which vary with regard to release competence. This thesis investigated the role of different ion channels in insulin secretion. β-cell-selective ablation of the CaV1.2 gene(βCaV1.2-/- mouse) decreased the whole-cell Ca2+ current by only ~45%, but almost abolished first-phase insulin secretion and resulted in systemic glucose intolerance. High-resolution capacitance measurements of exocytosis in single β-cells revealed that the loss of first-phase insulin secretion in the βCaV1.2-/- mouse was associated with the disappearance of a rapid component of exocytosis reflecting fusion of secretory granules physically attached to the CaV1.2 channel. A 20% reduction in glucose-evoked insulin secretion was observed in CaV2.3-knockout (CaV2.3–/–) islets, close to the 17% inhibition by the R-type blocker SNX482. Genetic or pharmacological CaV2.3 ablation strongly suppressed second-phase secretion in vitro, as well as in vivo, whereas first-phase secretion was unaffected. Suppression of the second phase coincided with an 18% reduction in oscillatory Ca2+ signaling and a 25% reduction in granule recruitment after completion of the initial exocytotic burst in single CaV2.3–/– β-cells. Intracellular ClC-3 chloride channels have been implicated in the process of making insulin granules release-competent, a process referred to as priming. Analysis of insulin secretion in vivo and in vitro as well as capacitance measurements revealed that the secretory response of ClC-3 deficient β-cells was reduced, but not abolished. The presence of ClC-3 in insulin granules was detected in a high-purification fraction of LDCVs obtained by phogrin-GFP labelling. In conclusion: (1) CaV1.2 Ca2+ channels are required for first-phase insulin release and maintenance of systemic glucose tolerance. (2) CaV2.3 Ca2+ channels play an important role in second-phase insulin release. (3) ClC-3 chloride channels facilitate insulin secretion by enhancing properly acidification of insulin granules needed for granule priming

Multi‐Channel Lanthanide Nanocomposites for Customized Synergistic Treatment of Orthotopic Multi‐Tumor Cases

Simultaneous photothermal ablation of multiple tumors is limited by unpredictable photo-induced apoptosis, caused by individual intratumoral differences. Here, a multi-channel lanthanide nanocomposite was used to achieve tailored synergistic treatment of multiple subcutaneous orthotopic tumors under non-uniform whole-body infrared irradiation prescription. The nanocomposite reduces intratumoral glutathione by simultaneously activating the fluorescence and photothermal channels. The fluorescence provides individual information on different tumors, allowing customized prescriptions to be made. This enables optimal induction of hyperthermia and dosage of chemo drugs, to ensure treatment efficacy, while avoiding overtherapy. With an accessional therapeutic laser system, customized synergistic treatment of subcutaneous orthotopic cancer cases with multiple tumors is possible with both high efficacy and minimized side effects

SUR1 Regulates PKA-independent cAMP-induced Granule Priming in Mouse Pancreatic B-cells.

Measurements of membrane capacitance were applied to dissect the cellular mechanisms underlying PKA-dependent and -independent stimulation of insulin secretion by cyclic AMP. Whereas the PKA-independent (Rp-cAMPS–insensitive) component correlated with a rapid increase in membrane capacitance of ~80 fF that plateaued within ~200 ms, the PKA-dependent component became prominent during depolarizations >450 ms. The PKA-dependent and -independent components of cAMP-stimulated exocytosis differed with regard to cAMP concentration dependence; the Kd values were 6 and 29 µM for the PKA-dependent and -independent mechanisms, respectively. The ability of cAMP to elicit exocytosis independently of PKA activation was mimicked by the selective cAMP-GEFII agonist 8CPT-2Me-cAMP. Moreover, treatment of B-cells with antisense oligodeoxynucleotides against cAMP-GEFII resulted in partial (50%) suppression of PKA-independent exocytosis. Surprisingly, B-cells in islets isolated from SUR1-deficient mice (SUR1-/- mice) lacked the PKA-independent component of exocytosis. Measurements of insulin release in response to GLP-1 stimulation in isolated islets from SUR1-/- mice confirmed the complete loss of the PKA-independent component. This was not attributable to a reduced capacity of GLP-1 to elevate intracellular cAMP but instead associated with the inability of cAMP to stimulate influx of Cl- into the granules, a step important for granule priming. We conclude that the role of SUR1 in the B cell extends beyond being a subunit of the plasma membrane KATP-channel and that it also plays an unexpected but important role in the cAMP-dependent regulation of Ca2+-induced exocytosis

Why treatment fails in type 2 diabetes.

Erik Renström and colleagues discuss a new mouse study that explores the mechanism behind the secondary failure of sulfonylurea treatment

Impacts of Inter-Basin Water Transfer Projects on Optimal Water Resources Allocation in the Hanjiang River Basin, China

Inter-basin water transfer project is an effective engineering countermeasure to alleviate the pressure of water supply in water-deficient areas and balance the uneven distribution of water resources. To assess the impacts of inter-basin water transfer projects on optimal water resources allocation, an integrated water resources management framework is proposed, and is applied to the middle and lower reaches of the Hanjiang River Basin in China. Firstly, future water demands are analyzed as inputs. Then, a multi-objective water resources allocation model is formulated mitigating the negative impacts of water transfer projects on downstream water quantity and quality by using the non-dominated sorting genetic algorithm-II (NSGA-II). Finally, the indicators of water supply reliability, vulnerability and resilience are evaluated under different scenarios of inter-basin water transfer projects. The results indicate that: (1) the reliability and resilience of the water donor system will be gradually reduced while the vulnerability will be increased with the expansion of water transfer projects and the increase of water demand, (2) water supply risk is likely to increase in all zones (because zones at the boundary cannot obtain sufficient water due to limitations of local inflow and reservoir operation, while the amount of water available in the zones along the mainstream river is directly decreased by the water transfer projects), (3) more water supply measures and compensation measures will need to be implemented in the water donor areas. The framework proposed in this study to evaluate the comprehensive impact of inter-basin water transfer projects is conducive to water resources management

Glucose dependence of insulinotropic actions of pituitary adenylate cyclase-activating polypeptide in insulin-secreting INS-1 cells.

The cAMP-elevating pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates insulin release in pancreatic B-cells. Here, we have investigated its potentiating action in rat insulinoma INS-1 cells. In intact cells, PACAP-27 (100 nM) stimulated glucose-induced insulin secretion by >60%. Using the patch-clamp technique with single-cell exocytosis monitored as increases in cell capacitance, we observed that at 10 mM and 20 mM extracellular glucose, PACAP-27 acted mainly by a >50% enhancement of depolarization-elicited Ca(2+) entry, whereas at low (3 mM) glucose, the predominant effect of the peptide was a twofold increase in Ca(2+) sensitivity of insulin exocytosis. The latter effect was mimicked by glucose itself in a dose-dependent fashion. PACAP-27 exerts a prolonged effect on insulin secretion that is dissociated from changes of cytoplasmic cAMP. Whereas an elevation of cellular cAMP content (135%) could be observed 2 min after addition of PACAP-27, after 30 min preincubation with the peptide, cAMP concentrations were not different from basal. Yet, such pretreatment with PACAP-27 stimulated subsequent insulin release by congruent with60%. This sustained action is likely to reflect an increased degree of protein-kinase-A-dependent phosphorylation, and inhibitors of the kinase largely prevented the PACAP-mediated effects