A FURTHER STUDY OF THE ELECTRIC RESPONSES OF SMOOTH MUSCLE

Abstract

The electric responses obtained from the nictitating membrane on stimulation of the cervical sympathetic nerve, from the fundus of the urinary bladder on stimulation of the pelvic nerve (parasympathetic), and from the pilomotors of the tail on stimulation of the abdominal sympathetic chains, were recorded. A direct-coupled amplifier allowed a more accurate study of the latencies and durations of the various potentials obtained than had been previously reported [see B. A. 8(1) : entry 827]. A systematization of the potentials in response to a single shock into 4 components, I, II, IIIa and IIIb, is given in place of the previous classification, "initial" and "delayed" potentials. Potential I corresponds to the former initial potential and to the spike potential of striated muscle. Potential II was not clearly distinguished from the initial or delayed responses in the previous paper. It follows I almost immediately and either slightly precedes contraction or is simultaneous with it. IIIa follows II during contraction and may be monophasic, diphasic or polyphasic, becoming repetitive in some cases. IIIb correspends to the delayed potential previously descr. It is a long, slow wave which follows closely the course of contraction. IIIb is not an artefact dependent upon changes of resistance due to changes of contact of the electrodes, or due to changes of shape and blood supply of the tissue during contraction. The results recently reported by Monnier and Bacq (1935) and Bacq and Monnier (1935) are discussed with reference to the schema presented here. A correlation of the potentials I, II, IIIa and IIIb with the physiology of chemical mediation is tentatively suggested.