Intracellular acidosis decreases the outward Na(+)-Ca2+ exchange current in guinea pig ventricular myocytes.
The Na(+)-Ca2+ exchange transport operating in outward mode has been suggested to cause Ca2+ entry during reperfusion or reoxygenation, exchanging extracellular Ca2+ for intracellular Na+ that has accumulated during ischemia or cardioplegia. During cardioplegia, however, an increase in Ca2+ entry via this mechanism can be decreased due to increased intracellular H+ activity and a decrease in cellular ATP content. In this study giant excised cardiac sarcolemmal membrane patch clamp technique was employed to investigate the effect of cytosolic pH change on the Na(+)-Ca2+ exchanger, excluding the effect of ATP, in guinea pig cardiac myocytes. The outward Na(+)-dependent current, which has a characteristics of Hill equation, was decreased as pH was decreased in the range of 7.5-6.5. The current density generated by the Na(+)-Ca2+ exchange transport was 56.6 +/- 4.4 pA/pF (Mean +/- S.E.M.) at pH 7.2 and decreased to 42.9 +/- 3.0 pA/pF at pH 6.9. These results imply that Na(+)-Ca2+ exchange transport, operating in a reverse mode during cardioplegia, decreases due to increased intracellular H+, and further suggest that consequent intracellular Na+ accumulation is one of aggravating factors for Ca2+ influx during reoxygenation or reperfusion.
Lee
E H
EH
Department of Physiology, Inha University College of Medicine, Inchon, Korea.
Park
S R
SR
Paik
K S
KS
Suh
C K
CK
D000138:Acidosis / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004553:Electric Conductivity; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport; D009206:Myocardium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000502:physiology
D017923:Sodium-Hydrogen Exchangers; D012964:Sodium; D002118:Calcium