Nicotinic Acid Adenine Dinucleotide Phosphate (NAADP) and Endolysosomal Two-pore Channels Modulate Membrane Excitability and Stimulus-Secretion Coupling in Mouse Pancreatic β Cells *

摘要

Background: TPCs are regulated by NAADP and other factors. Results: NAADP-induced Ca~(2+)release from acidic stores evokes depolarizing currents in pancreatic β cells. Inhibition of NAADP signaling or TPC knock out attenuates Ca~(2+)signaling and insulin secretion. Conclusion: NAADP-evoked Ca~(2+)release enhances β cell excitability and insulin secretion in response to glucose or sulfonylureas. Significance: NAADP signaling pathways offer novel therapeutic targets for diabetes treatment. Pancreatic β cells are electrically excitable and respond to elevated glucose concentrations with bursts of Ca~(2+)action potentials due to the activation of voltage-dependent Ca~(2+)channels (VDCCs), which leads to the exocytosis of insulin granules. We have examined the possible role of nicotinic acid adenine dinucleotide phosphate (NAADP)-mediated Ca~(2+)release from intracellular stores during stimulus-secretion coupling in primary mouse pancreatic β cells. NAADP-regulated Ca~(2+)release channels, likely two-pore channels (TPCs), have recently been shown to be a major mechanism for mobilizing Ca~(2+)from the endolysosomal system, resulting in localized Ca~(2+)signals. We show here that NAADP-mediated Ca~(2+)release from endolysosomal Ca~(2+)stores activates inward membrane currents and depolarizes the β cell to the threshold for VDCC activation and thereby contributes to glucose-evoked depolarization of the membrane potential during stimulus-response coupling. Selective pharmacological inhibition of NAADP-evoked Ca~(2+)release or genetic ablation of endolysosomal TPC1 or TPC2 channels attenuates glucose- and sulfonylurea-induced membrane currents, depolarization, cytoplasmic Ca~(2+)signals, and insulin secretion. Our findings implicate NAADP-evoked Ca~(2+)release from acidic Ca~(2+)storage organelles in stimulus-secretion coupling in β cells.