The beta subunit modulates potassium activation of the Na-K pump.
We recently cloned the alpha 1 and the beta 1 and beta 3 subunits of the Na,K-ATPase of the toad Bufo marinus. To investigate possible functional differences between beta 1 and beta 3, we studied the potassium activation of Na-K pumps expressed in the oocyte of Xenopus laevis. Na-K pump activity was measured as K(+)-induced current in voltage-clamped oocytes. We could take advantage of the relative resistance to ouabain conferred by the Bufo alpha subunit to study specifically the exogenously expressed Na-K pumps after inhibition of the ouabain-sensitive endogenous Xenopus Na-K pumps. Coinjection of Bufo alpha 1 subunit cRNA with either beta 1 or beta 3 cRNAs results in the expression of functional Na-K pumps that share similar low ouabain sensitivity but differ in their K+ half activation constant (K1/2). Similar results were obtained with Xenopus alpha 1 and beta 1 or beta 3 subunits and with Bufo/Xenopus heterodimers. We conclude that some specific sequence of the beta subunit can influence the activation of the Na,K pump by extracellular K+ ions.
Jaisser
F
F
Institut de Pharmacologie et de Toxicologie, Lausanne, Switzerland.
Horisberger
J D
JD
Rossier
B C
BC
D000818:Animals; D002024:Bufo marinus; D004789:Enzyme Activation; D007700:Kinetics; D046911:Macromolecular Substances; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology*; D014982:Xenopus laevis
D046911:Macromolecular Substances; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium