A transient outward current in a mammalian central neurone blocked by 4-aminopyridine

Abstract

It is becoming increasingly clear that nerve cells in the mammalian central nervous system (CNS) have a very complex electroresponsiveness. They exhibit not only time- and voltage-dependent Na⁺ and K⁺ conductances, analogous to those in the squid giant axon¹, but also a variety of other conductances that have a significant role in the control of cell excitability. Of the outward currents, there are, in addition to the delayed rectifier, the Ca²⁺-activated K⁺ current^2,3 which underlies the long-lasting spike afterhyperpolarization, and the M current⁴, a non-inactivating K⁺ current evoked by membrane depolarization and blocked by muscarinic, cholinergic agonists. We demonstrate here the existence in a mammalian central neurone (hip-pocampal CA3 pyramidal cells) of yet another outward current, which is transient and may be carried by K⁺ ions. Further, the experiments show that this current is substantially reduced by the convulsant 4-aminopyridine (4-AP)⁵, resulting in a marked increase in cell excitability.