Characterization of palytoxin-induced channels in mouse neuroblastoma cells

Palytoxin-induced whole-cell and single channel currents were recorded in mouse neuroblastoma cells. Palytoxin-induced single channel currents had a slope conductance of 26 pS (20-22 degrees C). Palytoxin-induced channels were permeable to sodium and potassium and slightly permeable to calcium, choline and tetramethylammonium. They did not seem to be significantly permeable to chloride or protons. Both the steady-state and the rate of the dose-dependent effects of palytoxin could be accounted for if one assumed that a palytoxin-induced channel resulted from the binding of two palytoxin molecules to a membrane receptor with respective dissociation constants of 5 nM and 10 pM. In the continued presence of low palytoxin concentrations (less than 1 nM) the effect was maintained. Higher palytoxin concentrations induced a transient and irreproducible effect. The effect of palytoxin was decreased when either external sodium was replaced by potassium or in the absence of calcium in external and/or internal media. The results suggest that ionic currents result from the binding of palytoxin molecules to a membrane receptor and that receptor-toxin complexes can be internalized.