LIANG, Wenbin*; WANG, Rui; Department of Physiology, University of Saskatchewan,Saskatoon,Canada; Department of Physiology, University of Saskatchewan, Saskatoon,Canada: Hydrogen sulfide-modulated calcium homeostasis in pancreatic beta cells

Hydrogen sulfide (H2S) is endogenously produced in pancreatic beta cells, but its physiological roles in regulating beta cell function are unclear. In the present study, INS-1E cells (a pancreatic beta cell line) were loaded with fura-2 AM or fluo-3 AM and intracellular free Ca2+ levels ([Ca2+]i) were measured using an epifluorescence or confocal microscope. H2S at a physiologically relevant concentration (100 ÁM) significantly decreased basal [Ca2+]i from 109.2▒10.4 nM to 84.5▒3.7 nM (n=6, p<0.01). Effects of H2S were blocked by 10 ÁM gliclazide, but mimicked by 100 ÁM diazoxide (108.3▒10.4 nM vs. 76.2▒4.6 nM, n=7, p<0.01), which were plasma membrane ATP-sensitive K+ (KATP) channel blocker and opener, respectively. After blocking KATP channels with gliclazide or removing extracellular Ca2+, H2S increased [Ca2+]i by 26.6▒2.7% and 26.8▒6.3%, respectively. Studies with rhodamine 123 revealed that H2S depolarized mitochondrial membrane potential (MMP) by 22.3▒1.2% (n=8, p<0.01), which was blocked by 59.5▒5.5% by cyclosporin A (a blocker for mitochondrial permeability transition pore, PTP). Depolarizing MMP with 2 ÁM FCCP caused a 32.6▒3.4% increase in [Ca2+]i (n=6, p<0.01), by releasing mitochondrial Ca2+ pool. The effects of H2S on [Ca2+]i were not significantly affected by depleting endoplasmic reticulum Ca2+ pool with thapsigargin (n=4). Our results suggest that H2S reduces [Ca2+]i by attenuating extracellular calcium entry via opening KATP channels. On the other hand, H2S depolarizes MMP partially by opening PTP, leading to calcium release from mitochondria. H2S may be an important modulator of calcium homeostasis and mitochondrial function of pancreatic beta cells. [Supported by NSERC and Gasotransmitter REsearch And Training (GREAT) Program, Canada]