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. Na+-independent pHi recovery from an acid load (NH3/NH4+) was rapid (0.53 ± 0.14 pH U/min; n = 5) and could be inhibited by luminal application of H+ pump inhibitors, NEM, N,N′-dicyclohexylcarbodiimide, or bafilomycin (0.08 ± 0.08 pH U/min; P < 0.05). Thus H+ secretion in the mesonephric collecting tubule occurs at high rates and is mediated by cells possessing polarized H+/ HCO3- transporters in a distribution similar to that of the metanephric α-intercalated cell, with apical H+-ATPase and basolateral Cl-/HCO3- exchangers.

Original languageEnglish
Pages (from-to)F979-F986
JournalAmerican Journal of Physiology - Renal Fluid and Electrolyte Physiology
Issue number6 36-6
StatePublished - Dec 1994


  • Anion exchanger
  • Bicarbonate ion transport
  • Cell pH
  • Development
  • Endocytosis
  • Hydrogen ion-adenosinetriphosphatase
  • In vitro microperfusion
  • Intercalated cell
  • Kidney
  • Rabbit
  • Total carbon dioxide


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