Comparative aspects of membrane properties and innervation of longitudinal and circular muscle layers of rabbit jejunum.

Longitudinal muscle of the rabbit jejunum usually generated burst discharges, whereas circular muscle mainly generated slow potential change. Membrane potential was higher, and the space and time constants were larger in circular muscle than in longitudinal muscle. Current-voltage relationship exhibited anomalous rectification by depolarization of membrane in longitudinal muscle cells, and delayed rectification in most circular muscle. Excitatory junction potentials (e.j.p.s) were recorded from both muscles and inhibitory junction potentials (i.j.p.s) were recorded from only circular muscle. The e.j.p.s consisted of muscarinic e.j.p.s and atropineresistant e.j.p.s, but only the latter were recorded from circular muscle. The i.j.p.s were not affected by either or both alpha- and beta-blockers, but were blocked by TTX. From mechanical and electrical responses of both muscle layers induced by field stimulation, it was postulated that four different types of nerve fibres innervate the jejunum muscles: (I) cholinergic excitatory nerves, (II) non-adrenergic and non-cholinergic inhibitory nerves (or purinergic nerves), (III) non-adrenergic and non-cholinergic excitatory nerves and (IV) adrenergic inhibitory nerves. In the longitudinal muscle, (I) was dominant, but (II) was also found. In the circular muscle all four types were found to exist. Effects of adrenergic nerve stimulation on the membrane potential was not detected by stimulation below 10 Hz, although externally applied noradrenaline at 5.9 X 10(-8)m had a relaxing effect.