AJP - Cell Physiology, Vol 254, Issue 6 C751-C758, Copyright © 1988 by American Physiological Society

ARTICLES

Vascular smooth muscle Na+-H+ exchanger kinetics and its activation by angiotensin II

G. A. Vallega, M. L. Canessa, B. C. Berk, T. A. Brock and R. W. Alexander
Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115.

We have studied the kinetic properties of basal and angiotensin II (ANG II)-stimulated Na+-H+ exchange in cultured rat aortic smooth muscle cells. Initial rates of 22Na+ influx were measured in the presence of ouabain (1 mM) and bumetanide (0.1 mM) with and without amiloride after intracellular acidification by preincubation in Na-free media. The kinetics of amiloride (100 microM)-sensitive Na+ influx were studied under the following conditions: 1) constant intracellular pH (pHi; 6.8) and varying external Na+ (Na+o), which gave a Km of 23.6 +/- 2.0 (SD, n = 3) mM and a maximum velocity (Vmax) of 25 nmol.mg protein-1.min-1 (varying the amiloride concentration gave a Ki of 22 microM for inhibition under these conditions); and 2) constant Na+o (100 mM) and varying pHi (from 7.4 to 6.2), which indicated that amiloride-sensitive Na+ influx was stimulated by cell acidification when an outward H+ gradient was imposed. ANG II-stimulated amiloride-sensitive Na+ influx for up to 30 min with a half-maximal activation 10(-8) M. The pHi dependence from cell pH (pHi 7.2-6.2) of amiloride-sensitive Na+ influx stimulated by ANG II was similar to that of the basal values, a finding indicating that ANG II did not change the affinity of Na+-H+ exchange for intracellular H+. However, at pHi 6.8, ANG II increased the Vmax of amiloride-sensitive Na+ influx from 25 to 33 nmol.mg protein-1.min-1 and markedly decreased the Km for Na+o from 23.6 +/- 7.4 to 3.7 (SD, n = 4; P less than 0.005) mM.(ABSTRACT TRUNCATED AT 250 WORDS)

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