Ion concentrations in the rat CCD: differences between cell types and effect of alkalosis

We have previously shown that the isolated perfused cortical collecting duct (CCD) from chloride-depleted alkalotic (CDA) rats continues to secrete HCO3 for up to 3 h. To determine whether the sustained alteration in transport was associated with changes in intracellular ion concentrations, we performed energy-dispersive X-ray microanalysis in microdissected tubule bundles obtained from CDA rats and rats with normal acid-base status (CON). Before analysis, the bundles from both groups were incubated for 1 h in vitro in a modified Ringer solution (pH 7.4, 105 mM Cl). Principal (PC) and intercalated cells (IC) of the CCD from CON animals differed in the nuclear concentration of Na (17.0 vs. 24.7 mmol/l cell water), K (192.5 vs. 177.0 mmol/l cell water), and Cl (17.8 vs. 47.8 mmol/l cell water). Cells of the cortical thick ascending limb of Henle (CTAL) had the lowest Na and Cl values (11.5 and 14.8 mmol/l cell water, respectively). CDA resulted in no systematic Cl changes. In the IC the nuclear Na concentration was significantly increased (32.0 vs. 24.7 mmol/l cell water) and in all cells a small reduction in K concentration was detectable. These findings suggest that 1) the different transport functions of IC, PC, and CTAL are associated with differences in the intracellular ion composition, and 2) the sustained HCO3 secretion seen in CCD from CDA rats cannot be explained as the result of intracellular Cl depletion.