Voltage-dependent inhibition of the Na+,K+ pump by tetraethylammonium

Tetraethylammonium (TEA(+)) is an effective inhibitor of a variety of K+-channels, and has been widely used to reduce K+-sensitive background conductances in electrophysiological investigations of the Na+,K+-ATPase. Here we demonstrate by combination of two-electrode voltage clamp (TEVC) and giant patch clamp of Xenopus oocytes, and measurements of the activity of purified ATPase of pig kidney that TEA(+) directly inhibits the Na+,K+-ATPase from the outside. The K-I value in TEVC experiments at 0 mV is about 10 mM increasing with more negative potentials. A similar voltage-dependent inhibition by TEA(+) was observed in the excised membrane patches except that the apparent K-I value at 0 mV is about 100 mM, a value nearly identical to that found for inhibition of purified kidney ATPase. The voltage-dependent inhibition can be described by an effective valency of 0.39 and is attributed to an interference with the voltage-dependent binding of K+ at an external access channel. The apparent dielectric length of the access channel for K+ is not affected by TEA(+). (C) 1998 Elsevier Science B.V. All rights reserved.