Principal cells of cortical collecting ducts of the rat are not a route of transepithelial Cl? transport

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Abstract
The rat cortical collecting duct (CCD) exhibits high rates of NaCl reabsorption when stimulated by mineralocorticoid and antidiuretic hormone (ADH). The present study was undertaken to determine if there is significant transcellular Cl− movement across the principal cells of the rat CCD. CCDs were dissected from kidneys of rats that had been injected with deoxycorticosterone (5 mg, i.m.) 2–9 days prior to the experiment. The ducts were perfused in vitro with identical perfusing and bathing solutions, except that 200 pmol.l−1 ADH was added to the bathing solutions. The basolateral membrane voltage (PDbl) of principal cells was −77±1 mV and the luminal membrane voltage (PD1) was −68±1 mV (mean ± SEM, n=124). Separate impalements with single-barrelled Cl−-selective microelectrodes gave an apparent intracellular Cl− activity of principal cells of 17±2 mmol.l−1. Transepithelial PD and PDbl were unaffected by luminal furosemide, hydrochlorothiazide (HCT), 4-acetamido-4-isothiocyanostilbene2,2-disulphonic acid, (SITS), or the Cl− channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB); bath addition of SITS or the Cl− channel blocker diphenylamino-2-carboxylic acid; or replacement of bath HCO 3 − by Cl−. The intracellular Cl− activity (a cell Cl ) also remained unchanged with the addition of HCT, SITS or the Cl− channel blockers to either the perfusing or bathing solutions, or with replacement of the bathing solution HCO 3 − . With Cl− replacement in both solutions, a cell Cl decreased to 9 mmol.l−1, but not until after 4–6 min, indicating a very low rate of Cl− transport in these cells, even under conditions of maximal stimulation of NaCl reabsorption by mineralocorticoid plus ADH. The remaining a cell Cl could be attributed to interference with the Cl− selective electrodes by other cytosolic anions. We conclude that a cell Cl of principal cells in the rat CCD is not far above passive equilibrium, and that these cells do not contribute significantly to transepithelial Cl− reabsorption, which must occur by alternative routes such as the paracellular pathway, and/or through intercalated cells.

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