The K ATP channel is critical for calcium sequestration into non-ER compartments in mouse pancreatic beta cells

Abstract

K ATP channel activity influences beta cell Ca 2+ homeostasis by regulating Ca 2+ influx through L-type Ca 2+ channels. The present paper demonstrates that loss of K ATP channel activity due to pharmacologic or genetic ablation affects Ca 2+ storage in intracellular organelles. ATP depletion, by the mitochondrial inhibitor FCCP, led to Ca 2+ release from the endoplasmic reticulum (ER) of wildtype beta cells. Blockade of ER Ca 2+ ATPases by cyclopiazonic acid abolished the FCCP-induced Ca 2+ transient. In beta cells treated with K ATP channel inhibitors FCCP elicited a significantly larger Ca 2+ transient. Cyclopiazonic acid did not abolish this Ca 2+ transient suggesting that non-ER compartments are recruited as additional Ca 2+ stores in beta cells lacking K ATP channel activity. Genetic ablation of K ATP channels in SUR1KO mice produced identical results. In INS-1 cells transfected with a mitochondrial-targeted Ca 2+ -sensitive fluorescence dye (ratiometric pericam) the increase in mitochondrial Ca 2+ evoked by tolbutamide was 5-fold larger compared to 15 mM glucose. These data show that genetic or pharmacologic ablation of K ATP channel activity conveys Ca 2+ release from a non-ER store. Based on the sensitivity to FCCP and the property of tolbutamide to increase mitochondrial Ca 2+ it is suggested that mitochondria are the recruited store. The change in Ca 2+ sequestration in beta cells treated with insulinotropic antidiabetics may have implications for beta cell survival and the therapeutic use of these drugs. Copyright © 2007 S. Karger AG.