[Ca2+ channels and the abnormal electrical activity of demyelinated nerve]

Peripheral nerve demyelination was produced in adult rats by placing loosely-constrictive ligatures around the common sciatic nerve. The postoperative behavior of these rats indicated that hyperalgesia, allodynia and possible spontaneous pain were produced. In the meantime, abnormal spontaneous afferent activities (ectopic firings)originating from the demyelinated region were recorded. Evidence showed that the application of Ca2+ and Ca2+ channel blockers modulated the abnormal activity of the injured nerve. Ca2+ facilitation was dependent on its concentration (in the range of 10-20 mol/L), while 40mol/L Ca2+ always abolished firing. Verapamil, as well as La3+, applied locally or i. v. (for verapamil) not only strongly inhibited the spontaneous ectopic firings, but also blocked discharges elicited by tetraethylammonium. It is suggested that newly formed Ca2+ channels on the naked axolemma are largely responsible for the abnormal afferent activities following demyelination of the nerve.