An analysis of the transmission of excitation from autonomic nerves to smooth muscle

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Abstract
An analysis has been made of the transmission of excitation from the hypogastric nerve to the smooth muscle cells of the guinea-pig vas deferens. Depolarization of single muscle cells with current pulses from an intracellular electrode gave local depolarizations of the cell membrane which were not propagated. The total membrane resistance after 100 msec, of depolarization was 15 M[OMEGA] for depolarizations between 10 and 40 mV. Depolarization of some cell membranes with a current pulse during the excitatory junction potential (EJP) decreased the amplitude of the EJP from about 10 mV at 20 mV depolarization, to nearly 0 at 60 mV depolarization. In some cells the EJP was unchanged during depolarizations of 50 m. The action of transmitter on the smooth muscle cell membrane continued for the duration of the EJP. Action potentials which occurred at various times during the EJP failed to remove the remaining phases of the EJP. It was shown that the slow time course of the EJP could not be due to the instantaneous and simultaneous release of transmitter from a number of relatively distant sources. It was shown that each smooth muscle cell was Innervated by several axons. The serial sections examined with the electron microscope showed that a smooth muscle had either a single axon terminating-within 200 A of the muscle or no axons terminating on it at all. Therefore transmitter must be released along the length of the axons as well as at the terminations of the axons.

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