Evidence of a K+-H+-ATPase in vascular smooth muscle cells

R. D. McCabe, D. B. Young

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Abstract

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 μeq/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 (pH(i)) of CRA VSMC was reduced 0.14 ± 0.03 U by NC-1300-B and 0.22 ± 0.03 U by NEM. pH(i) 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')- 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 pH(i) by extruding H+ in exchange for K+, and is presumably a K+-H+-ATPase similar to those described in other tissues.

Original languageEnglish
Pages (from-to)H1955-H1958
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Volume262
Issue number6 31-6
DOIs
StatePublished - 1992

Keywords

  • NC-1300-B
  • SCH28080
  • intracellular pH
  • omeprazole
  • potassium ion transport

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