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 nimodipine on the decremental response in rabbits with experimental autoimmune myasthenia. Nimodipine produced an immediate augmentation of the decremental response to 3-Hz nerve stimulation, which lasted about 30 min. In contrast, verapamil caused marked amelioration of the decrement beginning 30 min after injection. Our findings are consistent with previous reports suggesting that verapamil has a presynaptic effect of enhanced acetylcholine release at the neuromuscular junction. Since evaluation of a drug effect in vivo in animals with experimental autoimmune myasthenia gravis may be more pertinent to its effect on patients with myasthenia gravis (MG), verapamil might prove to be safer in MG than nimodipine. However, due to the additional effects of calcium channel blockers, the safety of their use in myasthenia gravis cannot be inferred from the experimental results.