Electrical properties of a purified complex of α-latrotoxin and its receptor incorporated into planar lipid bilayers

Abstract

Membrane reconstitution experiments have been performed using artificial membranes of soybean lecithin in order to determine the physiological role played in the neuronal membrane by α-LTx binding protein, recently purified from solubilized bovine synaptosomal membranes. When unilamellar liposomes (with and without the reconstituted receptor, which had been preincubated with α-Latrotoxin) were added to the aqueous phase of a planar lipid bilayer, they induced a stepwise increase in conductance. The effects of α-LTx on the receptor-bearing membranes were compared with those induced by the toxin in the control membranes. For the receptor-bearing membranes, the mean latent period preceding the appearance of the toxin-induced channels was considerably shorter, and macroscopic currents were fifty times larger at lower concentrations of α-Latrotoxin. In addition, there was a change in the voltage dependence of the current, and the appearance of conductance steps at positive voltages was observed. These results suggest that the role of the receptor is twofold: it facilites the transmembrane insertion of the toxin, and modulates the properties of the resulting channels.