AJP - Renal Physiology, Vol 264, Issue 4 655-F661, Copyright © 1993 by American Physiological Society
Metabolic cost of bafilomycin-sensitive H+ pump in intact dog, rabbit, and hamster proximal tubules
J. Noel, P. Vinay, A. Tejedor, A. Fleser and R. Laprade
Departement de Medecine, Hopital Notre-Dame de Montreal, Universite de Montreal, Quebec, Canada.
Bafilomycin A1 is a specific inhibitor of the brush-border membrane-bound
H(+)-adenosinetriphosphatase (H(+)-ATPase) of the kidney cortex with no
effect on the mitochondrial ATP synthetase or on the basolateral
Na(+)-K(+)-ATPase activities. Bafilomycin A1 is thus a useful tool to
estimate the contribution of the activity of the H(+)-ATPase to the
cellular ATP turnover in a suspension of proximal tubules containing
largely S1 and S2 segments. In dog proximal tubules incubated under control
conditions, we found that 81% of the respiration is directly related to ATP
synthesis, i.e., is sensitive to oligomycin (phosphorylative respiration).
Of this amount, 29% is inhibited by 5 x 10(-7) M bafilomycin A1 alone and
90-95% by the combination of bafilomycin plus ouabain. These results
indicate that the H(+)-ATPase activity is a significant energy-requiring
process in dog proximal tubules. If bafilomycin is added after a 5- to
7-min preincubation with 1 mM ouabain, then the bafilomycin-sensitive ATP
turnover is larger, reaching 44% of total phosphorylation. This may suggest
that the H+ pump is stimulated by the indirect inhibition of the Na+/H+
exchanger produced by the exposure of tubules to ouabain. The contribution
of the bafilomycin-sensitive H+ pump to the cell ATP turnover is also
increased by acidification of the extracellular medium. In rabbit and
hamster proximal tubules, the bafilomycin-sensitive ATP requirement
involves only 5 and 10%, respectively, of the total ATP turnover. These
results demonstrate that the metabolic cost of proton secretion by the
membrane-bound H(+)-ATPase in suspensions of proximal tubules may be
considerable but varies significantly from species to species.
