Glucagon is a potent counterregulatory hormone that opposes the action of insulin in controlling glycemia. The cellular mechanisms by which pancreatic α-cell glucagon secretion occurs in response to hypoglycemia are poorly known. SUR1/K_IR6.2-type ATP-sensitive K⁺ (K_ATP) channels have been implicated in the glucagon counterregulatory response at central and peripheral levels, but their role is not well understood. In this study, we examined hypoglycemia-induced glucagon secretion in vitro in isolated islets and in vivo using Sur1KO mice lacking neuroendocrine-type K_ATP channels and paired wild-type (WT) controls. Sur1KO mice fed ad libitum have normal glucagon levels and mobilize hepatic glycogen in response to exogenous glucagon but exhibit a blunted glucagon response to insulin-induced hypoglycemia. Glucagon release from Sur1KO and WT islets is increased at 2.8 mmol/liter glucose and suppressed by increasing glucose concentrations. WT islets increase glucagon secretion approximately 20-fold when challenged with 0.1 mmol/liter glucose vs. approximately 2.7-fold for Sur1KO islets. Glucagon release requires Ca²⁺ and is inhibited by nifedipine. Consistent with a regulatory interaction between K_ATP channels and intra-islet zinc-insulin, WT islets exhibit an inverse correlation between β-cell secretion and glucagon release. Glibenclamide stimulated insulin secretion and reduced glucagon release in WT islets but was without effect on secretion from Sur1KO islets. The results indicate that loss of α-cell K_ATP channels uncouples glucagon release from inhibition by β-cells and reveals a role for K_ATP channels in the regulation of glucagon release by low glucose.

Background: The objective of our work was to investigate both the contractile function and the release of ATP and NO from strips of bladder tissue after removal of the urothelium.Methods: The method of removal was a gentle swabbing motion rather than a sharp surgical cutting to separate the urothelium from the smooth muscle. The contractile response and ATP and NO release were measured in intact as well as on swabbed preparations. The removal of the urothelial layer was affirmed microscopically.Results: After the swabbing, the smaller contractions were evoked by electrical as well as by chemical stimulation (50 μM carbachol or 50 μM α, β meATP). Electrical stimulation, carbachol and substance P (5 μM) evoked lower release of ATP in the swabbed strips than in intact strips. Although release of NO evoked by electrical stimulation or substance P was not changed, release of NO evoked by carbachol was significantly less in the swabbed preparations.Conclusion: Since swabbing removes only the urothelium, the presence of the suburothelial layer may explain the difference between our findings and those of others who found an increase in contractility. Evoked release of ATP is reduced in swabbed strips, indicating that ATP derives solely from the urothelium. On the other hand, electrical stimulation and substance P evoke identical degrees of NO release in both intact and swabbed preparations, suggesting that NO can be released from the suburothelium. Conversely, carbachol-induced release of NO is lower in swabbed strips, implying that the cholinergic receptors (muscarinic or nicotinic) are located in the upper layer of the urothelium.

Background and Purpose— ATP-sensitive K ⁺ (K _ATP ) channels have been implicated in the mechanism of neuronal ischemic preconditioning. To evaluate the role of neuronal/β–cell-type K _ATP channels, SUR1 null (Sur1KO) mice lacking (K _IR 6.x/SUR1) ₄ K _ATP channels were subjected to a preconditioning protocol with the use of double carotid occlusion. Methods— Wild-type C57BL/6 and Sur1KO mice were subjected to a double carotid block for 40 minutes with or without a 20-minute preconditioning block. After a 10-day reperfusion period, damage was assessed histologically in the hippocampal CA1, CA2, and CA3 areas and in the dentate gyrus. The neuroprotective effects of intracerebroventricular injections of diazoxide, which selectively affects mitochondria versus opening SUR1-type K _ATP channels, and 5-hydroxydecanoate, a selective blocker of mitoK _ATP channels, were evaluated with the same protocol. Results— Neurons in the CA1 region of both Sur1KO and wild-type animals subjected to a 20-minute ischemic insult were protected equally from neuronal damage produced by a subsequent 40-minute ischemic period. Pretreatment with diazoxide protected both Sur1KO and wild-type neurons, while 5-hydroxydecanoate augmented neurodegeneration in both strains of animals when administered before a 20-minute bout of ischemia. Conclusions— SUR1-based K _ATP channels are not obligatory for neuronal preconditioning or augmentation of neurodegeneration by 5-hydroxydecanoate.