Intracellular Na⁺ activates a K⁺ channel in mammalian cardiac cells

Abstract

In a wide variety of cells, various intracellular agents, such as Ca²⁺ (refs 1,2), ATP^3,4 and cyclic nucleotides^5,6, regulate ionic conductances of the membrane. In cardiac cells, the intracellular Na⁺ concentration ([Na⁺]_i) frequently increases when a disturbance occurs in the electrogenic Na–K pump activity or the Na–Ca exchange mechanism. We have investigated a possible role of [Na⁺]_i in controlling ion channels by using a patch-clamp method⁷, and have found a K⁺ channel that is gated by [Na⁺]_i >20mM, but not by the intracellular Ca²⁺ concentration (∼10⁻⁴M). We report here that the channel has a unitary conductance of 207 ± 19 pS(n = 16) with K⁺ concentrations of 150 mM outside and 49 mM inside, and shows no detectable voltage-dependent kinetics. The Na⁺-activated K⁺ channel represents a novel class of ionic channel.