Evidence for coupling between Na+ pump activity and TEA-sensitive K+ currents in Xenopus laevis oocytes.
Using the two-microelectrode voltage clamp technique in Xenopus laevis oocytes, we estimated Na(+)-K(+)-ATPase activity from the dihydroouabain-sensitive current (IDHO) in the presence of increasing concentrations of tetraethylammonium (TEA+; 0, 5, 10, 20, 40 mM), a well-known blocker of K+ channels. The effects of TEA+ on the total oocyte currents could be separated into two distinct parts: generation of a nonsaturating inward current increasing with negative membrane potentials (VM) and a saturable inhibitory component affecting an outward current easily detectable at positive VM. The nonsaturating component appears to be a barium-sensitive electrodiffusion of TEA+ which can be described by the Goldman-Hodgkin-Katz equation, while the saturating component is consistent with the expected blocking effect of TEA+ on K+ channels. Interestingly, this latter component disappears when the Na(+)-K(+)-ATPase is inhibited by 10 microM DHO. Conversely, TEA+ inhibits a component of IDHO with a KD of 25 +/- 4 mM at +50 mV. As the TEA(+)-sensitive current present in IDHO reversed at -75 mV, we hypothesized that it could come from an inhibition of K+ channels whose activity varies in parallel with the Na(+)-K(+)-ATPase activity. Supporting this hypothesis, the inward portion of this TEA(+)-sensitive current can be completely abolished by the addition of 1 mM Ba2+ to the bath. This study suggests that, in X. laevis oocytes, a close link exists between the Na-K-ATPase activity and TEA(+)-sensitive K+ currents and indicates that, in the absence of effective K+ channel inhibitors, IDHO does not exclusively represent the Na(+)-K(+)-ATPase-generated current.
Huang
H
H
Groupe de recherche en transport membranaire, University of Montreal, Quebec.
St-Jean
H
H
Coady
M J
MJ
Lapointe
J Y
JY
D000818:Animals; D002462:Cell Membrane / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure; D004594:Electrophysiology; D005260:Female; D008564:Membrane Potentials / Q000502:physiology; D009865:Oocytes / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D010042:Ouabain / Q000031:analogs & derivatives / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000032:analysis / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology*; D014982:Xenopus laevis / Q000502:physiology*
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; C000977:dihydroouabain; D010042:Ouabain; D019789:Tetraethylammonium; D000254:Sodium-Potassium-Exchanging ATPase