Effects of Bufalin and Related Cardiotonic Steroids in the Neuromuscular Junction

Abstract

Bufosteroids, bufalin (4−5 × 10−5 g/ml), cinobufagin (7 × 10−5) and resibufogenin (1 × 10−4) showed a neuromuscular block in rat isolated diaphragm preparations, while digitoxigenin and ouabain showed no such block. A block of the twitch induced by direct stimulation was observed in the denervated preparations only. Presumably, bufalin can be classified as a depolarizing blocking agent such as succinyl-choline, however, differed in the following: blocking effect was potentiated in a bath deficient in sodium ions; it was sensitive to stimulus frequency change; lower doses of bufalin increased the post-tetanic potentiation and antagonized the blocking effect induced by magnesium. These findings suggest that bufalin has a pre-synaptic effect presumably concerned with the bufalin-induced block.