Abstract
Pancreatic islets were isolated from noninbred
ob
ob
mice and used for evaluating how removal of extracellular Na
+ affects
45Ca fluxes in the insulin-producing β cells. Isoosmotic replacement of Na
+ with Li
+ was less efficient in stimulating the incorporation of intracellular (La
3+ non-displaceable)
45Ca than substitution with choline
+ or sucrose. Ample support for the significance of Na
+Ca
2+ exchange for the net efflux of Ca
2+ was obtained with the observation that Na
+ deprivation markedly inhibited the
45Ca washout in a Ca
2+-deficient medium. The inhibitory action of Na
+ deficiency exceeded that obtained with 20 m
m glucose. The
45Ca incorporated after removal of Na
+ differed from that taken in response to glucose in not being exhanged with the Ca
2+ entering the β cells during glucose stimulation and in appearing also in the postmicrosomal supernatant obtained by differential centrifugation.
