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Heterologous expression of the Na + ,K + ‐ATPase γ subunit in Xenopus oocytes induces an endogenous, voltage‐gated large diameter pore
Author(s) -
Sha Qun,
Lansbery Kristan L.,
Distefano Darcy,
Mercer Robert W.,
Nichols Colin G.
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.t01-1-00407.x
Subject(s) - biophysics , conductance , xenopus , gamma subunit , hyperpolarization (physics) , chemistry , ouabain , divalent , protein subunit , membrane potential , biochemistry , stereochemistry , sodium , biology , physics , organic chemistry , nuclear magnetic resonance spectroscopy , gene , condensed matter physics
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 Ba 2+ ( K i = 0.7 m m ) and Ca 2+ ( K i = 0.4 m m ). 4 2‐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 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 Ca 2+ ‐ and voltage‐gated, non‐selective, large diameter pores that are intrinsically present within the oocyte membrane.