Ouabain-induced cell swelling in rabbit cortical collecting tubule: NaCl transport by principal cells

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Abstract
Ouabain had no effect on the volume of intercalated cells of DOCA-stimulated rabbit cortical collecting tubules, but caused principal cells to swell rapidly at an initial rate of 67% min., Principal cells swelled 133% then activated regulatory volume decrease mechanisms and shrank at an initial rate of −3%/min to a new volume 13% above control. The initial rate of ouabain swelling was completely inhibited by perfusate Na+ removal or reduced 95% by luminal addition of 10−5 m amiloride. Luminal peritubular, or bilateral Cl− removal each caused cell shrinkages of 10% and reduced the rate of ouabain swelling by 70, 85, and 99%, respectively. The presence of an apical Cl− transport step in principal cells was confirmed by increasing luminal K+ from 5 to 53mm, which caused cell swelling of 22%. This volume increase was completely blocked by luminal Cl− removal, but was unaffected by peritubular Cl− substitution. Perfusion of CCT with 0.1mm acetazolomide, 0.1mm DPC or 0.5mm SITS caused principal cell shrinkages of 7–9% and reduced the rate of ouabain swelling by 60, 70, and 40%, respectively. The initial rate of ouabain swelling was inhibited 70% by bilateral CO2/HCO3 removal and 50% by whole animal acid loading. Taken together these results demounstrate that ouabain swelling is due to cellular NaCl accumulation and that Na+ enters the cell primarily through apical Na+ channels. Cellular Cl− entry occurs at least partially through the apical membrane and may be mediated by a Cl−/HCO 3 − exchanger. Brief (45–90 sec) exposure of principal cells to ouabain is associated with a rapid inhibition of Na+ and/or Cl− entry steps, whereas long-term (>5min) ouabvain exposure completely blocks one or both of these transport pathways.