The electrophysiological characteristics of demyelinated axons are sensitive to changes in plasma calcium concentration. This study investigated the effect of verapamil, a calcium antagonist drug, on brainstem auditory, visual, and somatosensory evoked potentials in multiple sclerosis patients. Eight clinically stable patients with abnormal visual and/or brainstem auditory evoked potentials and four normal volunteers were studied. During intravenous infusions of verapamil (mean plasma concentration = 130.0 +/- 56.4 ng/ml), the latencies of peaks III and V were shortened (p less than 0.05) in multiple sclerosis patients with abnormally prolonged BAEPs. The I-III (delta = 0.08 ms), III-V (delta = 0.46 ms), and I-V (delta = 0.53 ms) interpeak intervals, and the P100 latency (delta = 10.15 ms) of the visual evoked potential were similarly affected in these patients. In contrast, normal evoked potentials of both multiple sclerosis patients and control subjects were not altered compared to baseline recordings obtained 24 hours earlier. Intravenous verapamil, therefore, alters the BAEPs and VEPs of some multiple sclerosis patients with demyelinated auditory and visual pathways by shortening pathologically prolonged latencies toward normal. The present study suggests pharmacological manipulation of calcium-dependent processes, possibly at the level of the demyelinated axon, can acutely facilitate central conduction of electrical impulses in some patients with clinically stable multiple sclerosis.
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