Palytoxin: effects on contractility and 45Ca2+ uptake in isolated ventricle strips

Palytoxin (PTX) inhibited phasic tension production and initiated tonic contracture in isolated paced ventricle strips at concentrations greater than 10(-10) M. PTX-induced contracture was associated with increased 45Ca2+ uptake. PTX-induced additional 45Ca2+ uptake was completely blocked by 2 mM La3+. All observed PTX effects were enhanced by elevation of [Ca2+] o from 1.9 to 6 mM and this threefold increase in [Ca2+] o resulted in a threefold increase in isotope-determined Ca2+ uptake in presence of 10(-8) M PTX. It is concluded that the observed effects of PTX could be mediated by an increase in calcium permeability of myocardial cells.