Clonidine promotes the accumulation of 45Ca in pancreatic beta-cell organelles

Glucose-stimulated insulin release from pancreatic islets of ob/ob-mice was inhibited by 10(-9) M of the alpha 2-adrenergic agonist clonidine. This inhibitory effect was abolished by 10(-7) M of the antagonist yohimbine. Loading the islets with 45Ca during the clonidine exposure followed by isolation of subcellular fractions under conditions known to minimize the 45Ca redistribution resulted in increased accumulation of the isotope in the mitochondrial and microsomal fractions. It is suggested that clonidine inhibits glucose-stimulated insulin release by increasing the organelle sequestration of Ca2+.