SOLUBILIZATION AND FUNCTIONAL RECONSTITUTION OF A CHLORIDE CHANNEL FROM TORPEDO-CALIFORNICA ELECTROPLAX

Chloride channels were detergent-extracted from Torpedo electroplax plasma membrane vesicles and reconstituted into liposomes by rapid detergent removal and a freeze-thaw-sonication procedure. Concentrative uptake of Cl-36-, driven by a Cl- gradient was used to determine conductance properties of reconstituted channels. Chloride flux assayed by this method is strongly selective for Cl- over cations, is blocked by SCN-, inactivated by treatment with DIDS, and exhibits an anion selectivity sequence Cl- > Br- > F- > SO4(2-), as does the voltage-gated Cl- channel from Torpedo observed in planar lipid bilayers. The channels are localized to the noninnervated face of the electrocyte, and a novel trapped-volume method is used to estimate a channel density on the order of 500 pmol/mg protein. An initial fractionation of the membrane extract by anion exchange chromatography yields fivefold enrichment of the channel activity.