NON-CHOLINERGIC, EXCITATORY JUNCTION POTENTIALS IN SMOOTH MUSCLE OF CHICKEN RECTUM

Muscle strips from the longitudinal or circular muscle of the chicken rectum were used to determine changes in membrane potential during field stimulation as recorded using the sucrose-gap method. Stimulation with single square pulses (0.1 msec duration) evoked junction potentials elicited by transmitter released from nerve endings. Facilitation in amplitude of excitatory junction potentials (EJPs) was seen during repetitive stimulation in the longitudinal muscle, but in the circular muscle, EJPs reduced. Neither atropine nor hyoscine (up to 10-5 g/ml) reduced EJPs. These drugs abolished the depression of EJPs in the circular muscle produced by repetitive stimulation. Anticholinesterases (2×10-8 2×10-6 g/ml) reduced the EJPs. The inhibitory effect was produced without affecting the membrane resistance of smooth muscle and was completely antagonized by atropine (10-6 g/ml). Drugs that abolish the adrenergic functions did not affect the EJPs. These results suggest that nerves involved in the EJPs are non-cholinergic and non-adrenergic in nature, and the motor transmission to the smooth muscle may be inhibited by cholinergic nerves, presumably presynaptically.