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

1. They subunit is a specific component of the plasmalemmal Na+, K+-ATPase. Like structurally related single-spanning membrane proteins such as cardia c phospholemman, Mat-8 and renal CHIF, large ion conductances are activated when gamma subunits are expressed in Xenopus oocytes. 2. Here we report critical properties of the gamma -activated conductance. The gamma -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 gamma -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 similar to 180), inulin (MW similar to 5000) and sper midine (MW similar to 148) efflux could occur through the gamma -activated conductance pathway, indicating a large pore diameter. In contrast, dextran -70 (MW similar to 70000) did not pass through the gamma -activated channel , indicating an upper limit to the pore size of similar to 50 Angstrom (5 n m). 5. Similar conductances that are permeable to large molecules were activate d by extreme hyperpolarization (>-150 mV) of uninjected oocytes. 6. We conclude that the Na+, K+-ATPase gamma subunits activate Ca2+- and vo ltage-gated, nonselective, large diameter pores that are intrinsically pres ent within the oocyte membrane.