The role of Na+/H+ exchange and the Na+/K+ pump in the regulation of [Na+]i during metabolic inhibition in guinea pig myocytes.
To investigate the mechanisms of Na+ loading during metabolic inhibition (MI), [Na+]i and pHi were measured in quiescent guinea pig myocytes using fluorescent probes, sodium-binding benzofuran isophthalate and 2,7,bis(carboxyethyl)-5,6-carboxyfluorescein. When myocytes were exposed to MI (3.3 mM amobarbital and 5 microM carbonyl cyanide m-chlorophenylhydrazone, without glucose) for 20 min, [Na+]i increased from 8.3 +/- 0.7 mM to 17.7 +/- 1.3 mM (p < 0.01) and pHi decreased from 7.22 +/- 0.03 to 7.00 +/- 0.04 (p < 0.05). The inhibition of Na(+)-H+ exchange by hexamethylene amiloride (HMA) significantly attenuated the increase in [Na+]i during MI (9.3 +/- 0.9 mM; p < 0.01 vs MI without HMA). When a K(+)-free solution was perfused to inhibit the Na+/K+ pump in the presence of HMA, there was an immediate increase in [Na+]i during MI. Perfusion of a K(+)-free solution after 10 min of MI caused no change in the rate of the increase in [Na+]i. We concluded that 1) Na+/H+ exchange was an important mechanism for Na+ elevation during MI, and 2) the Na+/K+ pump was functional during the early phase of MI, but was inhibited 10 min after MI in this model.
Katoh
H
H
Third Department of Internal Medicine, Hamamatsu University School of Medicine, Japan.
Satoh
H
H
Nakamura
T
T
Terada
H
H
Hayashi
H
H
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D002478:Cells, Cultured; D005260:Female; D005456:Fluorescent Dyes; D006168:Guinea Pigs; D006706:Homeostasis; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009132:Muscles / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D005456:Fluorescent Dyes; D017923:Sodium-Hydrogen Exchangers; C057360:5-(N,N-hexamethylene)amiloride; D000584:Amiloride; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase