Calcium dependence of membrane sealing at the cut end of the cockroach giant axon.

Following transection of a nerve fiber, the ruptured membrane must be resealed before regeneration from the proximal cut end. However, it is not certain how fast the cut end is resealed or how it is resealed. We have examined the membrane sealing process following transection of the cockroach giant axon, using recovery of decreased membrane potential and input resistance as criteria. The cable analysis and the injury current profile measured under voltage clamp suggested that the injured site is resealed by a structure with high electrical resistances 5 to 30 min after the transection. This recovery of membrane properties roughly coincided in time with the appearance of a partition-like structure formed near the cut end. The membrane resealing process was highly dependent upon temperature and extracellular Ca2+. Substitution of Ca2+ by equimolar Mg2+, Mn2+, or Sr2+ failed to induce the membrane sealing following transection. However, even in a Ca2+-free solution, the membrane resealing occurred if Ca2+ was injected into the axoplasm near the cut end. Thus, the membrane resealing appears to require Ca2+ entry into the axoplasm. The resealing process was not affected by colchicine or cytochalasin. However, the resealing was prevented by the application of phospholipase A2 inhibitors. These results suggest that the membrane resealing is triggered by phospholipase A2, which is activated by excess Ca2+ entering the axoplasm at the injured site.