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Altered Transport In Na/K pumps With α‐Subunits Truncated At Its 5 C‐Terminal Residues
Author(s) -
Yaragatupalli Siddhartha,
Gatto Craig,
Artigas Pablo
Publication year - 2009
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.23.1_supplement.798.2
Subject(s) - chemistry , xenopus , sodium , voltage clamp , membrane potential , intracellular , biophysics , analytical chemistry (journal) , biochemistry , chromatography , biology , gene , organic chemistry
Truncation of the α‐subunit's last 5 residues renders Na/K pumps with a reduced affinity for intracellular Na (Na i ), without effects on affinity for external K (K o ) (Morth et al, 2007). We used two electrode voltage clamp, and cut‐open oocyte to investigate the effect of the ΔKESYY truncation on electrogenic transport by Xenopus Na/K pumps (Q120RN131D‐α1+β3). Pump currents (I P ) were measured 2‐3 days after cRNA injection in Na i ‐loaded oocytes. The K 0.5 for I P activation by K o in Na‐free NMDG external solutions was ≈0.2 mM, both in eggs expressing truncated (TP) or normal (NP) pumps; TP expressing eggs showed larger I P (I Pmax ≈300 nA) than NP expressing eggs (I Pmax ≈150 nA). Western blots suggest better expression of TP at the plasma membrane. Surprisingly, in K o ‐free solutions, TP but not NP, presented a voltage‐ and Na o ‐dependent inward current of ≈ ‐250 nA at ‐160 mV with 135 mM Na o , that is reduced by ≈50% at 67 mM Na o . Consistent with a low Na o affinity in TP, the voltage‐dependent distribution of transient charge movement (which describes the E1‐E2 occupancy in the Na branch of transport) is shifted by ≈‐100 mV compared with NP. The effect of combining ΔKESYY with other mutations that modify external Na affinity will also be presented.