MOLECULAR CHARACTERIZATION OF A SWELLING-INDUCED CHLORIDE CONDUCTANCEREGULATORY PROTEIN, PL(CLN)

Cells maintain control of their volume by the passage of KCl and water across their membranes, but the regulatory proteins are unknown. Expr ession in Xenopus oocytes of a novel protein, pl(Cln), activated a chl oride conductance. We have cloned analogs of pl(Cln), from rat heart a nd Xenopus ovary. pl(Cln) was identified as an abundant soluble cytoso lic protein (similar to 40 kd) that does not immunolocalize with the p lasma membrane. pl(Cln) was found in epithelial and cardiac cells, bra in, and Xenopus oocytes, forming complexes with soluble actin and othe r cytosolic proteins. Monoclonal antibodies recognizing pl(Cln) blocke d activation of a native hypotonicity-induced chloride conductance (I- Cl.swell) in Xenopus oocytes, suggesting that pin, may link actin-boun d cytoskeletal elements to an unidentified volume-sensitive chloride c hannel. The high degree of sequence conservation and widespread expres sion of pl(Cln) suggest that it is an important element in cellular vo lume regulation.