AJP - Renal Physiology, Vol 247, Issue 2 339-F343, Copyright © 1984 by American Physiological Society
Increased Vmax for Na+/H+ antiporter activity in proximal tubule brush border vesicles from rabbits with metabolic acidosis
C. J. Tsai, H. E. Ives, R. J. Alpern, V. J. Yee, D. G. Warnock and F. C. Rector Jr
Na+/H+ antiporter activity in renal brush border vesicles from control
rabbits and rabbits made acidotic with 3 days of NH4Cl gavage was measured
using the acridine orange method. Acidotic rabbits exhibited a
significantly higher Vmax for antiporter activity (2.80 +/- 0.45
fluorescence units X s-1 X mg protein-1) compared with controls (1.31 +/-
0.13) but the Km for Na+ was unchanged (23.7 +/- 3.5 for acidotic, 19.1 +/-
3.2 mM for controls). When the Vmax for Na+/H+ antiporter activity was
considered in relation to the degree of acidosis achieved in the
experimental animals, there was a correlation (r = -0.75) between Vmax and
plasma total CO2 concentration. Amiloride (100 microM) inhibited Na+/H+
exchange (Na+ = 90 mM) by 59 +/- 7% in both control and acidotic animals,
indicating that the observed stimulation in Na+/H+ antiporter activity was
not due to increased electrically coupled cation exchange. These findings
suggest that the response of the proximal tubule to chronic metabolic
acidosis involves an adaptive increase in the Vmax for Na+/H+ antiporter
activity in the brush border membrane that is correlated to the degree of
acidosis in the animals.
