Na+ currents in cultured mouse pancreatic B-cells

Pancreatic B-cells, kept in culture for 1–4 days, were studied in the whole-cell, cell-attached and outside-out modes of the patch clamp technique. B-cells were identified by the appearance of electrical activity in the cell-attached mode when the bath glucose was raised from 3 to 20 mM. In whole-cell, 80% of these cells showed a transient inward Na+ current, when depolarizing pulses were preceded by holding potentials, or prepulses to potentials more negative than −80 mV. The midpoint (Eh) of the inactivation curve (h∞) was at −109 mV in 2.6 mM Ca2+, 1.2 mM Mg2+ and −120 mV in 0.2 mM Ca2+, 3.6 mM Mg2+. In 2.6 mM Ca2+, inactivation was fully removed atE<−150 mV. Na+ currents activated atE>−60 mV and were largest at around −10 mV (120 mM Na+). The kinetic parameters of activation (tp) and inactivation (τ)h were similar to those of other mammalian Na+ channels. Unitary currents with an amplitude of approximately 1 pA at −30 mV (140 mM Na+) with a similar voltage-dependence and time-course of mean current were recorded from outside-out patches. The results show that B-cells have a voltage-dependent Na+ current which, owing to the voltage-dependence of inactivation, is unlikely to play a major role in glucose-induced electrical activity.