Possible evidence for transmembrane K(+)-H+ exchange system in guinea pig myocardium.
The aim of this study was to obtain evidence for a transmembrane K(+)-H+ exchange system in Langendorff-perfused whole hearts and isolated ventricular myocytes of guinea pig. Effluent relation between K+ and pH in the whole hearts perfused with HEPES-buffered Tyrode's solution indicated a significant (p < 0.05) functional coupling of K+ uptake and H+ extrusion that was energy-dependent and omeprazole (OPZ)-sensitive. Administration of OPZ (0.3 mM) or dimethylamiloride (0.1 mM), an inhibitor of Na(+)-H+ antiport, to whole hearts subjected to the repetitive NH4Cl applications implied that both Na(+)-H+ and putative K(+)-H+ countertransports contribute to the regulation of intracellular pH. In isolated myocytes, voltage-dependent L-type Ca current (ICa) was inhibited by OPZ (0.3 mM) under K(-)- and Na(+)-free condition by 11 to 14%, and was inhibited to a greater extent (i.e., by 36 to 40%) by this agent in the presence of K+. OPZ-induced inhibition of the putative K(+)-H+ exchanger likely resulted in subsarcolemmal acidification which was responsible for the rate-independent suppression of ICa. In conclusion, these data provide functional evidence for a myocardial transmembrane K(+)-H+ exchanger.
Nagashima
R
R
First Department of Internal Medicine, Faculty of Medicine, Kyushu University School of Medicine, Fukuoka, Japan.
Tsuda
Y
Y
Maruyama
T
T
Kanaya
S
S
Fujino
T
T
Niho
Y
Y
D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D006168:Guinea Pigs; D017506:H(+)-K(+)-Exchanging ATPase / Q000378:metabolism*; D006706:Homeostasis; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D017136:Ion Transport; D008564:Membrane Potentials; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D009853:Omeprazole / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism*
D017506:H(+)-K(+)-Exchanging ATPase; D009853:Omeprazole; D011188:Potassium