The stimulus-secretion coupling of glucose-induced insulin release. XLIII. Na-Ca countertransport mediated by pancreatic islet native ionophores.

Native ionophores extracted from isolated pancreatic islets were able to transport Ca2+ from one aqueous medium into another across an organic immiscible phase. In the presence of a K+, Na+, Li+, or H+ gradient, Ca2+ was transported against its own concentration gradient from the medium of low monovalent-cation concentration to the opposite medium. The transport of Ca2+ was abolished by the organic calcium-antagonist suloctidil. These findings provide a model for the process of Na-Ca countertransport in islet cells and its inhibition in response to the conversion of nutrient secretagogues to their acidic metabolites.