Heterologous expression of the Na+,K+-ATPase γ subunit in Xenopus oocytes induces an endogenous, voltage-gated large diameter pore

1The γ subunit is a specific component of the plasmalemmal Na+,K+-ATPase. Like structurally related single-spanning membrane proteins such as cardiac phospholemman, Mat-8 and renal CHIF, large ion conductances are activated when γ subunits are expressed in Xenopus oocytes. 2Here we report critical properties of the γ-activated conductance. The γ-activated conductance showed non-selective cationic and anionic permeation, and extremely slow kinetics, with an activation time constant > 1 s following steps to -100 mV. 3The γ-activated conductance was inhibited by extracellular divalent ions including Ba2+ (Ki= 0.7 mm) and Ca2+ (Ki= 0.4 mm). 42-Deoxyglucose (MW ≈180), inulin (MW ≈5000) and spermidine (MW ≈148) efflux could occur through the γ-activated conductance pathway, indicating a large pore diameter. In contrast, dextran-70 (MW ≈70 000) did not pass through the γ-activated channel, indicating an upper limit to the pore size of ≈50 A (5 nm). 5Similar conductances that are permeable to large molecules were activated by extreme hyperpolarization (> -150 mV) of uninjected oocytes. 6We conclude that the Na+,K+-ATPase γ subunits activate Ca2+- and voltage-gated, non-selective, large diameter pores that are intrinsically present within the oocyte membrane.