SIMULTANEOUS FUNCTIONAL EXPRESSION OF SWELLING AND FORSKOLIN-ACTIVATED CHLORIDE CURRENTS IN PRIMARY CULTURES OF RABBIT DISTAL CONVOLUTED TUBULE

Ionic Cl- currents induced by cell swelling and forskolin were studied in primary cultures of rabbit distal convoluted tubule (DCTb) by the whole-cell patch clamp technique. We identified a Cl- conductance acti vated by cell swelling with an hyperosmotic pipette solution. The init ial current exhibited an outwardly rectifying I-V relationship, wherea s steady state current showed strong decay at depolarized membrane pot entials. The ion selectivity was I- > Bi- > Cl- > > glutamate. The for kolin-activated Cl- conductance demonstrated a linear I-V relationship and its ion selectivity was Br- > Cl- > I- > glutamate. This last con ductance could be related to the CFTR (cystic fibrosis transmembrane c onductance regulator) previously identified in these cells. NPPB inhib ited both Cl- currents, and DIDS inhibited only the swelling-activated Cl- current. Forskolin had no effect on the activation of the swellin g-activated Cl- current. In DCTb cells which exhibited swelling-activa ted Cl- currents subsequently inhibited by DIDS, forskolin could activ ate CFTR related Cl- currents. In the continuous presence of I- which inhibited CFTR conductance, forskolin did not modify the swelling-acti vated current. The results suggest that both Cl- conductances could be co-expressed in the same DCTb cell and that CFTR did not modulate the swelling-activated conductance.