VOLUME-ACTIVATED CHLORIDE CURRENTS IN PANCREATIC DUCT CELLS

We have used the patch clamp technique to study volume-activated Cl- c urrents in the bicarbonate-secreting pancreatic duct cell. These curre nts could be elicited by a hypertonic pipette solution (osmotic gradie nt 20 mOsm/l), developed over about 8 min to a peak value of 91 +/- 5. 8 pA/pF at 60 mV (n = 123), and were inhibited by a hypertonic bath so lution. The proportion of cells which developed currents increased fro m 15% in freshly isolated ducts to 93% if the ducts were cultured for 2 days. The currents were ATP-dependent, had an outwardly rectifying c urrent/voltage (I-V) plot, and displayed time-dependent inactivation a t depolarizing potentials. The anion selectivity sequence was: ClO4 = I = SCN > Pr = NO3 > CI > F > HCO3 > gluconate, and the currents were inhibited to a variable extent by DIDS, NPPB, dideoxyforskolin, tamoxi fen, verapamil and quinine. Increasing the intracellular Ca2+ bufferin g capacity, or lowering the extracellular Ca2+ concentration, reduced the proportion of duct cells which developed currents. However, remova l of extracellular Ca2+ once the currents had developed was without ef fect. Inhibiting protein kinase C (PKC) with either the pseudosubstrat e PKC (19-36), calphostin C or staurosporine completely blocked develo pment of the currents. We speculate that cell swelling causes Ca2+ inf lux which activates PKC which in turn either phosphorylates the Cl- ch annel or a regulatory protein leading to channel activation.