Palytoxin both Induces and Inhibits the Release of Histamine from Rat Mast Cells

Abstract
Palytoxin (PTX) is a potent releaser of histamine from rat mast cells. The concentration response curve is bell-shaped with its range between 0.05 ng/ml an 5 µg/ml and its maximum at 50 ng/ml. The release of histamine by PTX is specific because (a) heat-inactivated (50°C) mast cells are insensitive to PTX, and (b) extracellular calcium is essential. Removal of extracellular potassium as well as the presence of borate shifts the curve to the left by a factor of 10. At higher concentrations (5 µg/ml), PTX inhibits the release of histamine due to compound 48/80, MCD-peptide, Con-A, ionophore A-23187, and PTX itself.