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 KI 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 KI 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+.
Max-Planck Institut für Biophysik, Kennedyallee 70, D-60596 Frankfurt/Main, Germany.
U
U
Eckstein-Ludwig
J
J
Rettinger
L A
LA
Vasilets
W
W
Schwarz
D000818:Animals; D004553:Electric Conductivity; D004566:Electrodes; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D007668:Kidney / Q000201:enzymology; D008564:Membrane Potentials; D009865:Oocytes / Q000201:enzymology / Q000648:ultrastructure; D010042:Ouabain / Q000378:metabolism; D018408:Patch-Clamp Techniques; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*; D013552:Swine; D019789:Tetraethylammonium / Q000494:pharmacology*; D014982:Xenopus laevis
D004791:Enzyme Inhibitors; D010042:Ouabain; D019789:Tetraethylammonium; D000254:Sodium-Potassium-Exchanging ATPase