pH regulation of K(+) efflux from myocytes in isolated rat hearts: (87)Rb, (7)Li, and (31)P NMR studies.
This study investigates the effects of intracellular (pH(i)) and extracellular pH (pH(e)) on the efflux of Rb(+) and Li(+) in isolated rat hearts. (87)Rb and (7)Li NMR were used to measure Rb(+) and Li(+) content, respectively, of hearts, and (31)P NMR was used to monitor pH(i), pH(e), and phosphate levels. After 30-min equilibration with Rb(+) or Li(+), effluxes were initiated by switching perfusion to a Rb(+)- or Li(+)-free, high-K(+) (20.7 mM) Krebs-Henseleit buffer with 15 microM bumetanide. Monensin (2 microM) increased pH(i) from 7.10 +/- 0.05 to 7.32 +/- 0.07 and resulted in activation of Rb(+) efflux; the first-order rate constant (k x 10(3), in min(-1)) increased from 42 +/- 2 to 116 +/- 16. Glibenclamide (4 microM) did not inhibit monensin-activated Rb(+) efflux (k = 110 +/- 17), whereas quinine (0.2 mM) slightly inhibited it by 19 +/- 9%. Infusion of 15 mM NH(4)Cl during Rb(+) washout increased k for Rb(+) efflux by 93% (81 +/- 8), which was glibenclamide and quinine insensitive, and caused a transient increase in pH(i) to 7.25 +/- 0.08. Intracellular Li(+) inhibited NH(4)Cl-stimulated Rb(+) efflux by 55%. Monensin and NH(4)Cl stimulated Li(+) efflux by 40%, increasing k from 29 +/- 3 to 43 +/- 7 and 41 +/- 3, respectively. The stimulation was not sensitive to 10 microM dimethylamiloride. Intracellular acidosis that resulted from the washout of NH(4)Cl (pH 6.86 +/- 0.2) slightly inhibited Rb(+) efflux (k = 36 +/- 5), whereas NH(4)Cl itself in the absence of pH(i) changes did not markedly affect Rb(+) efflux. A moderate increase in pH(i) (7.17 +/- 0.06) produced by washout of 15 mM 2, 2-dimethylpropionate (DMP)-Tris from hearts preequilibrated with DMP did not markedly affect Rb(+) efflux. Neither global alkalosis (pH(i) 7.4, pH(e) 7.55) nor acidosis (pH(i) approximately pH(e) 6.8) produced by 3 mM Tris base or 5 mM MES, respectively, affected Rb(+) efflux. We suggest that intracellular alkalosis stimulates Rb(+) (K(+)) and Li(+) effluxes by activating a nonselective sarcolemmal K(+) (Li(+))/cation exchanger or a K(+) (Li(+))-anion symporter.
Institute for Biodiagnostics, National Research Council, Winnipeg, Manitoba, Canada R3B 1Y6. kupriyanov@ibd.nrc.ca
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Kupriyanov
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Xiang
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Kuzio
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Deslauriers
D000138:Acidosis / Q000378:metabolism; D000471:Alkalosis / Q000378:metabolism; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008094:Lithium; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008985:Monensin / Q000494:pharmacology; D009206:Myocardium / Q000166:cytology* / Q000378:metabolism*; D010758:Phosphorus; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012414:Rubidium Radioisotopes
D012414:Rubidium Radioisotopes; D000643:Ammonium Chloride; D010758:Phosphorus; D008985:Monensin; D008094:Lithium; D011188:Potassium