A slow voltage-activated potassium current in rat vagal neurons

Potassium currents play a key role in controlling the excitability of neurons. In this paper we describe the properties of a novel voltage-activated potassium current in neurons of the rat dorsal motor nucleus of the vagus (DMV). Intracellular recordings were made from DMV neurons in transverse slices of the medulla. Under voltage clamp, depolarization of these neurons from hyperpolarized membrane potentials (more negative than -80 mV) activated two transient outward currents. One had fast kinetics and had properties similar to A-currents. The other current had an activation threshold of around -95 mV (from a holding potential -110 mV) and inactivated with a time constant of about 3s. It had a reversal potential close to the potassium equilibrium potential. This current was not calcium dependent and was not blocked by 4-aminopyridine (5 mM), catechol (5 mM) or tetraethylammonium (20 mM). It was completely inactivated at the resting membrane potential. This current therefore represents a new type of voltage-activated potassium current. It is suggested that this current might act as a brake to repetitive firing when the neuron is depolarized from membrane potentials negative to the resting potential.