Regulation of 86Rb+ outflow from pancreatic islets. I. Reciprocal changes in the response to glucose, tetraethylammonium and quinine.

Glucose (16.7 mM), tetraethylammonium (TEA; 10.0 mM) and quinine (0.1 mM) all decreased 86Rb fractional outflow rate from isolated pancreatic islets. At the concentration here used, the effect of glucose was not augmented by TEA, suggesting that glucose affected the TEA-sensitive modality of Rb extrusion. The effects of TEA and quinine were not additive. In the presence of quinine which was as potent as glucose in decreasing 86Rb efflux, an early inhibition of 86Rb outlow was still observed in response to glucose administration. However, the latter inhibition was followed by a glucose-induced secondary rise in 86Rb fractional outflow rate. It is proposed that quinine unmasks a dual or discontinuous effect of glucose upon 86Rb+ handling by the islet cells.