Dominant role of sarcoendoplasmic reticulum Ca2+-ATPase pump in Ca2+ homeostasis and exocytosis in rat pancreatic beta-cells.
The exocytosis of insulin-containing granules from pancreatic beta-cells is tightly regulated by changes in cytosolic Ca2+ concentration ([Ca2+]i). We investigated the role of the sarcoendoplasmic reticulum Ca2+-ATPase (SERCA) pump, Na+/Ca2+ exchanger, and plasma membrane Ca2+-ATPase pump in the Ca2+ dynamics of single rat pancreatic beta-cells. When the membrane potential was voltage clamped at -70 mV (in 3 mm glucose at approximately 22 or 35 C), SERCA pump inhibition dramatically slowed (approximately 4-fold) cytosolic Ca2+ clearance and caused a sustained rise in basal [Ca2+]i via the activation of capacitative Ca2+ entry. SERCA pump inhibition increased ( approximately 1.8-fold) the amplitude of the depolarization-triggered Ca2+ transient at approximately 22 C. Inhibition of the Na+/Ca2+ exchanger or plasma membrane Ca2+-ATPase pump had only minor effects on Ca2+ dynamics. Simultaneous measurement of [Ca2+]i and exocytosis (with capacitance measurement) revealed that SERCA pump inhibition increased the magnitude of depolarization-triggered exocytosis. This enhancement in exocytosis was not due to the slowing of the cytosolic Ca2+ clearance but was closely correlated to the increase in the peak of the depolarization-triggered Ca2+ transient. When compared at similar [Ca2+]i with controls, the rise in basal [Ca2+]i during SERCA pump inhibition did not cause any enhancement in the magnitude of the ensuing depolarization-triggered exocytosis. Therefore, we conclude that in rat pancreatic beta-cells, the rapid uptake of Ca2+ by SERCA pump limits the peak amplitude of depolarization-triggered [Ca2+]i rise and thus controls the amount of insulin secretion.
Hughes
Elizabeth
E
Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
Lee
Andy K
AK
Tse
Amy
A
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism / Q000502:physiology*; D002462:Cell Membrane / Q000201:enzymology; D003600:Cytosol / Q000378:metabolism; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005089:Exocytosis; D006706:Homeostasis; D006873:Hydroquinones / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000201:enzymology* / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials; D010179:Pancreas; D051381:Rats; D017207:Rats, Sprague-Dawley; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019831:Sodium-Calcium Exchanger / Q000378:metabolism
D004791:Enzyme Inhibitors; D006873:Hydroquinones; D007328:Insulin; D019831:Sodium-Calcium Exchanger; C019359:2,5-di-tert-butylhydroquinone; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D002118:Calcium