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1 Physiology and Biophysics, Weill Medical College of Cornell U., New York, New York, United States
* To whom correspondence should be addressed. E-mail: lgpalm{at}med.cornell.edu.
Cl- currents were observed under whole-cell clamp conditions in cells of the rat cortical collecting duct (CCD), connecting tubule (CNT) and thick ascending limb of Henle's loop (TALH). These currents were much larger in intercalated cells compared with principal cells of the CCD, and were also larger in the TALH and in the CNT compared with the CCD. The conductance had no strong voltage dependence, and steady-state currents were similar in inward and outward directions with similar Cl- concentrations on both sides of the membrane. Current transients were observed, particularly at low Cl- concentrations, which could be explained by solute depletion and concentration in fluid layers next to the membrane. The currents had a remarkable selectivity among anions. Among halides, Br- and F- conductances were only 15% of that of the Cl-, and I- conductance was immeasurably small. SCN- and OCN- conductances were ~50%, and aspartate, glutamate and methanesulfonate conductances about 5% that of Cl-. No conductance could be measured for any other anion tested, including NO3-, HCO3-, formate, acetate or isethionate; NO3- and I- appeared to block the channels weakly. Conductances were diminished by lowering the extracellular pH to 6.4. The properties of the conductance fit best with those of the cloned renal anion channel ClC-K2, and likely reflect the basolateral Cl- conductances of the cells of these nephron segments.
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