HCO3- secretion in mitochondria-rich cells is linked to an H+-ATPase

Abstract

Turtle bladder mitochondria-rich (MR) cells secrete H+ by an ATP-dependent process. MR cells also secrete HCO3- by an energy-requiring, Cl- -dependent process that may depend on a serosal H+-ATPase. To determine whether HCO3- is linked to an H+-ATPase, O2 consumption was assessed in MR and granular (G) cells exposed to H+ and HCO3- transport inhibitors alone and also with an H+-ATPase inhibitor. MR and G cells were separated by Ficoll density-gradient centrifugation and treated with ouabain and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) to maximally inhibit Na+ and luminal H+ transport. O2 consumption was measured before and after cells were additionally treated with 10 microM N-ethylmaleimide (NEM), an inhibitor of nonmitochondrial H+-ATPase. O2 consumption of MR cells fell after treatment with NEM (delta = 8.64 +/- 2.35 microliters O2.h-1.mg protein-1, P less than 0.025, n = 5). There was no significant difference in G cells similarly treated (delta = 1.61 +/- 0.62 microliters O2.h-1.mg protein-1, P greater than 0.05, n = 5). Because luminal H+ secretion is nearly abolished after treatment with SITS, the decline in O2 consumption of 44.4 +/- 7.11% after addition of NEM is probably due to inhibition of other non-mitochondrial H+-ATPases. In the intact bladder, HCO3- secretion was reduced by 35.1% after serosal application of NEM. Furthermore, in SITS-treated MR and G cells, ATP levels as measured by the luciferin-luciferase assay method were not appreciably different in the presence or absence of NEM.(ABSTRACT TRUNCATED AT 250 WORDS)