Sodium-bicarbonate cotransporter NBCn1 in the kidney medullary thick ascending limb cell line is upregulated under acidic conditions and enhances ammonium transport

Academic Article

Abstract

  • In this study, we examined the effect of bicarbonate transporters on ammoniumammonia uptake in the medullary thick ascending limb cell line ST-1. Cells were treated with 1 mm ouabain and 0.2 mm bumetanide to minimize carrier-mediated NH transport, and the intracellular accumulation of C-methylammoniummethylammonia ( C-MA) was determined. In CO HCO -free solution, cells at normal pH briefly accumulated C-MA over 7 min and reached a plateau. In CO HCO solution, however, cells markedly accumulated C-MA over the experimental period of 30 min. This CO HCO -dependent accumulation was reduced by the bicarbonate transporter blocker, 4,4′- diisothiocyanatostilbene-2,2′-disulfonate (DIDS; 0.5 mm). Replacing Cl with gluconate reduced the accumulation, but the reduction was more substantial in the presence of DIDS. Incubation of cells at pH 6.8 (adjusted with NaHCO in 5% CO ) for 24 h lowered the mean steady-state intracellular pH to 6.96, significantly lower than 7.28 for control cells. The presence of DIDS reduced C-MA accumulation in control conditions but had no effect after acidic incubation. Immunoblotting showed that NBCn1 was upregulated after acidic incubation and in NH Cl-containing media. The Cl -HCO exchanger AE2 was present, but its expression remained unaffected by acidic incubation. Expressed in Xenopus oocytes, NBCn1 increased carrier-mediated C-MA transport, which was abolished by replacing Na . Two-electrode voltage clamp of oocytes exhibited negligible current after NH Cl application. These results suggest that DIDS-sensitive HCO extrusion normally governs NH NH uptake in the medullary thick ascending limb cells. We propose that, in acidic conditions, DIDS-sensitive HCO extrusion is inactivated, while NBCn1 is upregulated to stimulate NH transport. © 2010 The Physiological Society. 4 2 3 2 3 2 3 3 2 4 3 4 3 4 3 3 4 + 14 14 - 14 - 14 - - 14 - - 14 + - + - +
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    Digital Object Identifier (doi)

    Author List

  • Lee S; Lee HJ; Yang HS; Thornell IM; Bevensee MO; Choi I
  • Start Page

  • 926
  • End Page

  • 937
  • Volume

  • 95
  • Issue

  • 9