PROPERTIES OF JUNCTION POTENTIALS IN GASTRIC SMOOTH-MUSCLE OF THE RAT

In isolated smooth muscles of the rat stomach, the properties of elect rical responses of the membrane elicited by transmural nerve stimulati on were studied. The smooth muscle membranes were quiescent in the fun dus and spontaneously active with slow waves and often action potentia ls superimposed on top of the slow wave in the antrum and pylorus. The maximum membrane potentials were larger in the antrum (-50 to -55 mV) than in the fundus (-40 to -45 mV). Transmural nerve stimulation elic ited an excitatory junction potential (e.j.p.) which was followed by a n inhibitory junction potential (i.j.p.) in the fundus, and an i.j.p. alone in the antrum. The e.j.p. was inhibited by atropine, indicating that this potential was cholinergic in nature. The amplitude of the e. j.p. was increased by apamin or nitroarginine, and the latter was more potent than the former. The i.j.p. was inhibited by apamin or nitroar ginine, and was resistant to adrenergic and cholinergic blocking agent s, and therefore this potential was non-adrenergic non-cholinergic (NA NC) in nature. The inhibitory actions of nitroarginine on the i.j.p. w ere antagonized by L-arginine, suggesting the involvement of nitric ox ide (NO) in this junctional transmission. The results indicate that sm ooth muscles of the rat stomach receive cholinergic excitatory and NAN C inhibitory nerves, and that endogenous NO may either be partly respo nsible for the generation of the i.j.p. or may modulate the junctional transmissions.