Evidence for coupling between Na+ pump activity and TEA-sensitive K+ currents in Xenopus laevis oocytes |
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Authors: | H Huang H St-Jean M J Coady J -Y Lapointe |
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Institution: | (1) Groupe de recherche en transport membranaire, University of Montreal, H3C 3J7 Montreal, Quebec;(2) Physics Department, University of Montreal, C.P. 6128 succ. centre-ville, H3C 3J7 Montreal, Quebec |
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Abstract: | Using the two-microelectrode voltage clamp technique in Xenopus laevis oocytes, we estimated Na+-K+-ATPase activity from the dihydroouabain-sensitive current (I
DHO) 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 (V
M) and a saturable inhibitory component affecting an outward current easily detectable at positive V
M. 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 m DHO. Conversely, TEA+ inhibits a component of I
DHO with a k
d of 25±4 mm at +50 mV. As the TEA+-sensitive current present in I
DHO 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, I
DHO does not exclusively represent the Na+-K+-ATPase-generated current. |
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Keywords: | Na+-K+-ATPase Electrophysiology K+ channel Tetraethylammonium Conductance regulation |
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