Molecular Characterization of a Swelling-Induced Chloride Conductance Regulatory Protein, plcln

Cells maintain control of their volume by the passage of KCI and water across their membranes, but the regulatory proteins are unknown. Expression in Xenopus oocytes of a novel protein, plan, activated a chloride conductance. We have cloned analogs of pIa. from rat heart and Xenopus ovary. pIa. was ldentified as an abundant soluble cytosolic protein (40 kd) that does not immunolocalize with the plasma membrane. pIa. was found in epithelial and cardiac cells, brain, and Xenopus oocytes, forming complexes with soluble actin and other cytosolic proteins. Monoclonal antibodies recognizing plcln blocked activation of a native hypotonicity-induced chloride conductance (lc,.r~.,,) in Xenopus oocytes, suggesting that pin. may link actinbound cytoskeletal elements to an unidentified volume-sensitive chloride channel. The high degree of sequence conservation and widespread expression of plcln suggest that it is an important element in cellular volume regulation.