Evidence of a K(+)-H(+)-ATPase in vascular smooth muscle cells.
In earlier studies Na(+)-K(+)-adenosinetriphosphatase (ATPase) and Na(+)-K(+)-2Cl- cotransport partially accounted for vascular smooth muscle cell (VSMC) K+ (Rb+) uptake. In other cells Rb+ is taken up by a K(+)-H(+)-ATPase that is sensitive to NC-1300-B, SCH28080, omeprazole, and N-ethylmaleimide (NEM). This study examines the effects of K(+)-H(+)-ATPase inhibitors on VSMC. Rubidium uptake by primary cultures of canine coronary artery (CCA) VSMC or cultured rat aortic (CRA) VSMC line A7r5 was reduced 19-37% by NC-1300-B, SCH28080, or omeprazole. N-ethylmaleimide reduced CCA VSMC K+ content from 1.55 +/- 0.02 to 1.24 +/- 0.06 mu eq/mg protein. The NC-1300-B-sensitive portion of CRA VSMC Rb+ uptake was not blocked by ouabain (0.1 mM) or bumetanide (0.1 mM), but was reduced by alkalinization with 7.5 mM NH4Cl, and increased by acidification with 7.5 mM Na-acetate. Intracellular pH (pHi) of CRA VSMC was reduced 0.14 +/- 0.03 U by NC-1300-B and 0.22 +/- 0.03 U by NEM. pHi of CCA VSMC was reduced 0.20 +/- 0.03 U by omeprazole (1 mM) and 0.20 +/- 0.03 U or 0.20 +/- 0.05 U by amiloride in the absence or presence of omeprazole, respectively. Fluorescence of 2',7'-bis(carboxyethyl)-5-(6')- carboxyethyl)-5-(6')-carboxyfluorescein due to excitation at 500:441 nm in rat aortic strips was reduced by 0.21 +/- 0.02 U by omeprazole and 0.22 +/- 0.03 U by K+ removal and increased by 0.21 +/- 0.06 U by K+ repletion. We conclude that VSMC possess a previously unknown Rb+ uptake mechanism. This newly discovered mechanism helps to maintain K+ gradient and pHi by extruding H+ in exchange for K+, and is presumably a K(+)-H(+)-ATPase similar to those described in other tissues.
McCabe
R D
RD
Department of Physiology and Biophysics, University of Mississippi Medical Center, Jackson 39216-4505.
Young
D B
DB
D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D001011:Aorta / Q000166:cytology / Q000201:enzymology; D001562:Benzimidazoles / Q000494:pharmacology; D002460:Cell Line; D017506:H(+)-K(+)-Exchanging ATPase; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism; D009853:Omeprazole / Q000494:pharmacology; D051381:Rats; D012413:Rubidium / Q000493:pharmacokinetics; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors
D001562:Benzimidazoles; D007093:Imidazoles; C035235:Sch 28080; C057696:NC 1300 B; D000251:Adenosine Triphosphatases; D017506:H(+)-K(+)-Exchanging ATPase; D000254:Sodium-Potassium-Exchanging ATPase; D009853:Omeprazole; D012413:Rubidium