Effects of calcium channel blocking agents on neostigmine-induced fasciculations

Male Sprague-Dawley rats were anesthetized with pentobarbital and prepared for monitoring contractions of the gastrocnemius muscle evoked by stimulation of the sciatic nerve. Animals received atropine prior to a dose of neostigmine of 0.02 mg/kg i.v. The effects on contractile strength and the number of fasciculations in a 2-min period were assessed. Pretreatment with phenytoin, 20 mg/kg, reduced the number of fasciculations to 32% of control without altering contractile strength. Both nifedipine and nitrendipine, 1 mg/kg each, virtually abolished fasciculations without altering twitch strength. Verapamil, 4 and 8 mg/kg, depressed fasciculation frequency to 50% of control without affecting pre-neostigmine twitch height. The dihydropyridine calcium blocking agents did however reduce the neostigmine-induced augmentation of contraction strength. These data suggest that a calcium-mediated current at presynaptic motor endings participates in the generation of repetitive nerve terminal discharges leading to muscle fasciculations.