3 DISTINCT CHLORIDE CHANNELS CONTROL ANION MOVEMENTS IN RAT PAROTID ACINAR-CELLS

We used the whole-cell configuration of the patch clamp technique to e xamine the different macroscopic Cl- currents present in single rat pa rotid acinar cells. 2. Cell swelling produced by negative osmotic pres sure (hypotonic bath solutions) induced a large outwardly rectifying C l- current with little or no time and voltage dependence. In contrast, an increase in intracellular [Ca2+] induced by ionomycin activated Cl - currents with very different properties. Ca2+-activated Cl- currents showed outward rectification, relatively slow activation kinetics and marked voltage dependence. These results are consistent with the exis tence of two different outwardly rectifying Cl- channels in rat paroti d cells. 3. In conditions designed to eliminate the activation of thes e two Cl- currents, a third type of current was observed. This third c urrent was activated in a time-dependent manner by hyperpolarized pote ntials and was about equally permeant to Cl-, I- and Br-. 4. The prope rties of the hyperpolarization-activated current were similar to those of the cloned ClC-2 channel. Polymerase chain reaction-based methods and ribonuclease protection analyses indicated the presence in parotid gland of mRNA homologous to ClC-2. 5. Individual parotid acinar cells expressed all three types of Cl- channels. Each type of channel may c ontribute to Cl- efflux in distinct stages of the secretion process de pending on the intracellular [Ca2+], cell volume and membrane potentia l.