MECHANISMS OF PROXIMAL PROTON SECRETION IN BBM OF HERBIVOROUS, OMNIVOROUS, AND CARNIVOROUS SPECIES

The mechanisms of proton secretion by the proximal brush-border membra ne (BBM) were compared in carnivorous (dog), omnivorous (human, pig, r at), and herbivorous (rabbit, hamster) species. The activity of the pr oton pump (V-type bafilomycin-sensitive H+-adenosinetriphosphatase) an d of the Na+/H+ exchanger (amiloride-sensitive quenching of acridine o range fluorescence), the two major proton secretion mechanisms, was me asured. The enzymatic activity of the H+-adenosinetriphosphatase activ ity was measured in intact (endosomes) and solubilized (0.1% deoxychol ate or Triton X-100) BBM vesicles isolated by conventional Mg2+ precip itation techniques. In all species, but not in humans, the fraction of the ATP turnover energizing the proton pump (bafilomycin-sensitive re spiration) was also measured in isolated proximal tubules. Significant differences in acid transport mechanisms were noted between species, with the proton pump predominating in the BBM of carnivorous species a nd the Na+/H+ exchanger predominating in the BBM of herbivorous specie s. The fraction of respiration suppressible by bafilomycin in proximal tubules was also different in all the species considered. This may in dicate a different organization of proximal H+ transport related to th e species-specific menace to acid-base balance.