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 �M) 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 �M gliclazide, but mimicked by 100 �M diazoxide (108.3�10.4 nM vs. 76.2�4.6 nM, n=7, p<0.01), which were plasma membrane ATP-sensitive K⁺ (K_ATP) channel blocker and opener, respectively. After blocking K_ATP 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 �M 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 K_ATP 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]