CATION TRANSPORT BY PANCREATIC -CELLS: EFFECT OF 4-AMINOPYRIDINE ON ⁸⁶Rb⁺ AND ⁴⁵Ca²⁺ FLUXES

¹ Departamento de Fisiologia e Biofisica, Instituto de Biologia, Universidade Estadual de Campinas, 13.081, Campinas, S.P., Brasil

The effects of 4-aminopyridine (4-AP) on insulin release, glucose oxidation and ⁸⁶Rb⁺ and ⁴⁵Ca²⁺ fluxes of rat isolated islets were studied. 4-AP (0·1 and 1·0 mM) did not alter the ⁸⁶Rb⁺ fractional efflux. However, 10 mm 4-AP significantly increased the ⁸⁶Rb⁺ fractional efflux. 10 mM 4-AP also reduced the insulin release from islets incubated over 90 min in the presence of both 6 and 16·7 mM glucose and from perifused islet in the presence of 16·7 mM glucose. 4-AP (10 mM) only transiently increased the insulin release and the ⁴⁵Ca²⁺ fractional efflux in the presence of 6 mM glucose. The ⁴⁵Ca²⁺ fractional efflux was not changed when the islets were perifused at higher glucose concentration. At zero, 6 or 16·7 mM glucose, 4-AP (10 mM) significantly increased the 45Ca2+ net uptake by islets incubated for 90 min. 10 mM 4-AP significantly reduced the glucose oxidation of islets incubated for 120 min in the presence of 16·7 mM glucose. The effects of 10 mM 4-AP on the dynamics of insulin release and ⁸⁶Rb⁺ fractional efflux were poorly reversible. In conclusion, 4-AP, at concentrations that did not alter the glucose metabolism, (0·1 and 1 mM), failed to affect the K⁺ permeability in -cells as judged by the measurements of ⁸⁶Rb⁺ fractional efflux. At higher concentrations (10 mM) 4-AP increased ⁸⁶Rb⁺ efflux, decreased glucose metabolism and reduced insulin release.