[Effect of phoratoxin B on electrical and mechanical activities of the rat papillary muscle].
The effect of phoratoxin B(PH-TX), a small basic protein isolated from mistletoe, on transmembrane potentials and contraction of papillary muscles was studied using conventional intracellular microelectrodes. PHTX depolarized the resting potential, decreased the initial depolarizing phase of the action potential and the corresponding Vmax and lengthened the action potential duration. PHTX increased the amplitude of the contraction. The data suggest that PHTX effect is similar to that of cytotoxic or cardiotoxin molecules and may be related to a reversible blockade of Na, K-ATPase.