CHLORIDE CHANNELS IN APICAL MEMBRANE OF PRIMARY CULTURES OF RABBIT DISTAL BRIGHT CONVOLUTED TUBULE

Using the patch clamp technique on the apical membrane of primary cult ures of rabbit distal bright convoluted tubule cells (DCTb), two types of Cl- channel were identified. A small channel of 9 pS was observed in 9% of the patches. Cells pretreated with 1 mM 8-bromoadenosine 3',5 '-cyclic monophosphate (8-BrcAMP) or 5 mu M forskolin increased the ex pression of Cl- channels by 26 and 37%, respectively. In cell-attached and excised inside-out patches, the current-voltage (I-V) relationshi ps of the 9-pS channel were linear. In only 1 out of 47 active patches was the small-conductance Cl- channel still active 1 h after membrane excision. The addition of 0.1 mu M of the catalytic subunit protein k inase A with 2 mM ATP to the cytoplasmic side restored channel activit y in 8 out of 15 excised membrane patches. In 5 out of 467 patches of stimulated or nonstimulated cells, a larger Cl- conductance of 30 pS w as also recorded. In excised inside-out patches this channel outwardly rectified and was activated by strong depolarization. In cultured DCT b cells, the small-conductance, cAMP-activated Cl- channel shares many properties with the cystic fibrosis transmembrane conductance regulat or. Our results suggest that at least the small-conductance channel ma y participate in Cl- secretion across the apical membrane of DCTb in p rimary culture. This secretion may increase the rate of the apical Cl- /HCO3- exchange indirectly by enhancing the inwardly-directed Cl- grad ient.