Effect of phoratoxin B, a toxin isolated from mistletoe, on frog skeletal muscle fibres

Journal/Book: Toxicon 28 (1), 83-89. 1990;

Abstract: The effect of phoratoxin B on transmembrane potentials and currents offrog skeletal muscle was studied using intracellular microelectroderecording and double sucrose gap voltage clamp techniques. Phoratoxin Birreversibly depolarized the membrane. The depolarization wasinsensitive to tetrodotoxin, tetraethylammonium, 4-amino-pyridine,cesium, cadmium and D-600. In voltage clamp experiments, phoratoxin Binduced an inward resting current (Irest) which did not inactivate.Irest was blocked by increasing the external calcium concentration inthe Ringer solution; it was not blocked when Sr2+ replaced Ca2+.Analysis of the peak sodium current indicated that while both Ca2+ andSr2+ screen membrane surface charges, Ca2+ bound and reversed thephoratoxin B induced Irest whereas Sr2+ did not. The inward Irestinduced by phoratoxin B developed in the presence of external chlorideand remained unchanged in the presence of bicarbonate. The data suggestthat the depolarizing action of the toxin might be attributed to anincrease in the non-selective leak current and that it might act as adetergent. Author.

Keyword(s): ANIMAL

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