Sodium current in periglomerular cells of frog olfactory bulb in vitro

Abstract

Kinetic properties of the sodium current in periglomerular (PG) cells were investigated by applying whole-cell patch-clamp techniques to thin slices of the frog olfactory bulb. Eight of the cells were intracellularly stained with Lucifer Yellow for precise identification. Under current-clamp conditions PG cells showed rich spontaneous activity at rest. Na current was isolated from other current contributions by equimolar substitution of K + with Cs + in the intracellular solution to prevent K-currents, and 100 μM Cd 2+ in the external solution to block Ca-current. Depolarisations beyond −40 mV activated a fast transient TTX-sensitive inward current. Once activated, I Na declined exponentially to zero following a single exponential. The underlying conductance showed a sigmoidal activation between −40 and +30 mV, with half activation at −17.4 mV and a maximal value of 9.7 nS per neurone. The steady-state inactivation was complete at −30 mV and completely removed at −90 mV, with a midpoint at −56 mV. The activation process could be adequately described by third order kinetics, with time constants ranging from 260 μs at −20 mV to 70 μs at +50 mV.