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

1. The 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. 2. Here 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. 3. The γ-activated conductance was inhibited by extracellular divalent ions including Ba²⁺ (K_i = 0.7 mM) and Ca²⁺ (K_i = 0.4 mM). 4. 2-Deoxyglucose (MW Ο180), inulin (MW Ο5000) and spermidine (MW Ο148) efflux could occur through the γ-activated conductance pathway, indicating a large pore diameter. In contrast, dextran-70 (MW Ο70 000) did not pass through the γ-activated channel, indicating an upper limit to the pore size of Ο50 Å (5 nm). 5. Similar conductances that are permeable to large molecules were activated by extreme hyperpolarization (> -150 mV) of uninjected oocytes. 6. We 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.