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 (E_h) 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 (t_p) and inactivation ()_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.