H+ secretion in rabbit mesonephric collecting tubule

The mesonephros, the precursor of the metanephros, the definitive kidney, is the functional excretory organ in the 12- to 20-day-old rabbit fetus. It is believed to acidify allantoic fluid. To determine whether H+ excretion occurs in the distal nephron, we examined isolated perfused mesonephric collecting tubules by microcalorimetry and pH-sensitive fluorescent dyes. Collecting tubules secreted H+ (absorbed HCO3-) at rates twice those observed in the mature outer medullary collecting duct (OMCD) of the metanephric kidney. H+ secretion was not inhibited by ouabain (18.5 +/- 2.2 vs. 16.7 +/- 4.0 pmol.min-1.mm-1; n = 7, P = NS) but was reversibly inhibited by removing Cl- from the bathing solution (15.1 +/- 2.3 to -0.6 +/- 3.7 to 15.5 +/- 1.1 pmol.min-1.mm-1; n = 5, P < 0.05); luminal application of N-ethylmaleimide (NEM), an inhibitor of the H(+)-ATPase, also inhibited H+ secretion (n = 2). These results suggested that H+ secretion in the mesonephric collecting tubule is mediated by transporters similar to those of the OMCD. To test this hypothesis, we stained collecting tubules from 15-20 day embryos with 6-carboxyfluorescein (6-CF) diacetate to identify intercalated-like cells or perfused them with 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester (BCECF-AM) to measure intracellular pH (pHi). We found that 139 +/- 15 cells/mm concentrated 6-CF or BCECF, consistent with the phenotype of metanephric intercalated cells.(ABSTRACT TRUNCATED AT 250 WORDS)