Heterologous expression of the Na(+),K(+)-ATPase gamma subunit in Xenopus oocytes induces an endogenous, voltage-gated large diameter pore.
1. The gamma 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 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 Ba(2+) (K(i) = 0.7 mM) and Ca(2+) (K(i) = 0.4 mM). 4. 2-Deoxyglucose (MW approximately 180), inulin (MW approximately 5000) and spermidine (MW approximately 148) efflux could occur through the gamma-activated conductance pathway, indicating a large pore diameter. In contrast, dextran-70 (MW approximately 70 000) did not pass through the gamma-activated channel, indicating an upper limit to the pore size of approximately 50 A (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 gamma subunits activate Ca(2+)- and voltage-gated, non-selective, large diameter pores that are intrinsically present within the oocyte membrane.
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Department of Cell Biology and Physiology, Washington University School of Medicine, 660 South Euclid Avenue, St Louis, MO 63110, USA.
Lansbery
K L
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Distefano
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Mercer
R W
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Nichols
C G
CG
D000818:Animals; D000838:Anions / Q000378:metabolism; D000925:Anticoagulants / Q000493:pharmacokinetics; D000963:Antimetabolites / Q000493:pharmacokinetics; D001464:Barium / Q000493:pharmacokinetics; D002118:Calcium / Q000493:pharmacokinetics; D002412:Cations / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology; D003847:Deoxyglucose / Q000493:pharmacokinetics; D003911:Dextrans / Q000493:pharmacokinetics; D005110:Extracellular Space / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D007444:Inulin / Q000493:pharmacokinetics; D015640:Ion Channel Gating / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics* / Q000378:metabolism*; D013095:Spermidine / Q000493:pharmacokinetics; D014316:Tritium; D014981:Xenopus
D000838:Anions; D000925:Anticoagulants; D000963:Antimetabolites; D002412:Cations; D003911:Dextrans; D014316:Tritium; D001464:Barium; D007444:Inulin; D003847:Deoxyglucose; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium; D013095:Spermidine