Effect of Na+, K+ and Mg2+ on 45Ca+ uptake by pancreatic islets.

Microdissected pancreatic islets of noninbred ob/ob-mice were used to study ionic effects on the lanthanum-nondisplaceable 45Ca2+ uptake by islet cells. Omission of Mg2+ from the incubation medium had no effect, but the 45Ca2+ uptake was increased by omission of Na+ and decreased by omission of K+. Excess Mg2+ (1.2--15 mM) inhibited and excess K+ (4.7--25 mM) stimulated the 45Ca2+ uptake in a concentration-dependent manner. Stimulation of 45Ca2+ uptake in Na+-deficient islets was associated with an enhancement of the basal insulin release. Total abolishment of glucose-stimulated 45Ca2+ uptake in K+-deficient islets did not preclude a significant secretory reponse to glucose. It is concluded that the lanthanum-nondisplaceable 45Ca2+ uptake shows a partial correlation to insulin release.