The Action of Ryanodine on the Contractile Process in Striated Muscle

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Abstract
Two derivs. of Ryania speciosa, known as L8A2 which is a crude extract, and the purified ryanodine, were studied to determine their mode of action. The toxic symptoms were similar for both substances. In insects, ryanodine has a depressant effect, and high doses kill. Paralysis is accompanied by a tremendous increase in O2 consumption. Excitation and conduction in nerves, ganglia, and muscles are not affected by Ryania derivs. in the concns. used, which leaves the contractile process in muscle as the only possible site at which the extracts produce the paralytic action. It appears that ryanodine affects contractile processes before excitation and conduction are impaired. Ryania derivs. may interfere with either the glycolytic processes or with the high-energy phosphate system in striated muscle. The mode of action is probably one of interference with the phosphogen-ATP-ADP-actomyosin cycle during contraction.