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.