Persistence of extra-junctional sensitivity to acetylcholine after reinnervation by a foreign nerve in frog skeletal muscle.

Extra-junctional sensitivity to acetylcholine (ACh) was determined in fibres of the cutaneous pectoris (c.p.) muscle of adult Rana pipiens after denervation and subsequent reinnervation by either the original nerve or an implanted hypoglossal nerve. The mean sensitivity of denervated fibres was 89.1 (S.E. +/- 36) mV/nC which fell to 0.36 (S.E. +/- 0.21) mV/nC after reinnervation by the original nerve. In contrast the mean sensitivity of fibres after innervation by the implanted hypoglossal nerve was 21.4 (S.E. +/- 2.5) mV/nC. Stimulation of the implanted hypoglossal nerve in vitro evoked action potentials in many of the fibres in c.p. There was no apparent difference in extra-junctional sensitivity to ACh between those fibres in which hypoglossal stimulation evoked action potentials and those in which it did not. Recordings of electromyogram activity indicated that the implanted hypoglossal nerve evoked activity in the c.p. muscle in the intact animal. The significance of these results in relation to current theories of the ways in which nerves control muscle sensitivity to ACh is discussed.