Jun 22, 1976

Physostigmine-induced contractures in frog skeletal muscle

Pflügers Archiv : European journal of physiology
M K Pagala, A Sandow


Physostigmine in 15 mM concentration at pH 8.4 produces reversible contractures of up to 0.3 Po tension output in frog's whole toe muscle or in 7-10 fiber bundles of these muscles, At pH 7.2, the 15 mM physostigmine contracture output is only about 0.10 Po. The 15 mM, pH 8.4 contractures are essentially unaffected by lack of external Ca2+, complete depolarization of the fibers, detubulation by glycerol treatment, and 0 degrees C ambient temperature. These results and other evidence indicate that physostigmine produces contracture by directly releasing activator Ca2+ from the sarcoplasmic reticulum (SR). Pretreatment of muscles with 4 mM procaine reduces physostigmine's capacity to produce contracture, evidently by means of a competitive inhibition at SR sites. The above results indicate similarities between physostagmine and caffeine contractures. But the physostigmine action differs in that it is reversible, and, especially, it lacks the ability, strongly characteristic of caffeine, to sensitize a muscle to produce a rapid cooling contracture. The internal action of physostigmine requires that it be permeant, and, since it is a weak base (pKa = 8.2), this property is provided by its uncharged base. But, once internal, where th...Continue Reading

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Mentioned in this Paper

Rana pipiens
DRUG Screen Quant Caffeine
Cold Temperature
Resting Potentials
Sarcoplasmic Reticulum

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