VARIABLE EFFECT OF CALCIUM-CHANNEL BLOCKERS ON THE DECREMENTAL RESPONSE IN EXPERIMENTAL AUTOIMMUNE MYASTHENIA-GRAVIS

We tested the effect of intravenous administration of verapamil and ni modipine on the decremental response in rabbits with experimental auto immune myasthenia. Nimodipine produced an immediate augmentation of th e decremental response to 3-Hz nerve stimulation, which lasted about 3 0 min. In contrast, verapamil caused marked amelioration of the decrem ent beginning 30 min after injection. Our findings are consistent with previous reports suggesting that verapamil has a presynaptic effect o f enhanced acetylcholine release at the neuromuscular junction. Since evaluation of a drug effect in vivo in animals with experimental autoi mmune myasthenia gravis may be more pertinent to its effect on patient s with myasthenia gravis (MG), verapamil might prove to be safer in MG than nimodipine. However, due to the additional effects of calcium ch annel blockers, the safety of their use in myasthenia gravis cannot be inferred from the experimental results. (C) 1994 John Wiley and Sons, Inc.