Ionic channel distribution in regenerating mouse motor endings.

One of the nerves supplying the Triangularis sterni muscle of the adult mouse was crushed and focal extracellular recordings were made from the regenerating motor nerve terminals. Stimulation of the nerve elicited 4 types of signals depending upon the position of the electrode along the newly formed terminal branches. Specific ionic channel blockers were applied in the bath or iontophoretically to identify the nature of the different signal components. Sodium and potassium channels appeared to be located along most of the length of the newly formed terminals. This overlapping distribution differs considerably from their segregated localization previously described for mature endings. During maturation of regenerating endings, potassium channels disappear from the heminodal area and the density of sodium channels is greatly reduced along the remainder of the branches. Presynaptic evidence for polyneuronal reinnervation of single endplates is presented.