Neither a purine nor VIP is the mediator of inhibitory nerves of opossum oesophageal smooth muscle.

Abstract

SUMMARY1. Effects of stimulation of intramural nerves in the circular smooth muscle layer of the body of the oesophagus of the opossum (Didelphis marsupialis) were studied, simultaneously measuring the membrane potential of muscle cells using the sucrosegap technique and contractions of the muscle.2. Electrical field stimulation of the preparation, superfused with Krebs solution at 27 0C, induced a transient hyperpolarization of the smooth muscle cell membrane (i.j.p.) followed by a transient depolarization on which muscle action potentials were often superimposed. The muscle did not develop active tension spontaneously; it therefore did not relax during the i

Vasoactive intestinal polypeptide and non‐adrenergic, non‐cholinergic inhibition in lower oesophageal sphincter of opossum

“…These differed from the ij.ps recorded from body circular muscle (Daniel et al, 1983;Jury et al, 1985) in being smaller (cf: Table 2 and see Daniel et al, 1983;Jury et al, 1985) and lacking detectable after-depolarization (Figures 4 and 5). They were accompanied by a significant reduction in the magnitude of electrotonic potentials evoked by hyperpolarizing constant current pulses (Table 2 and Figure 4), indicating that there was a conductance increase.…”

“…It is of interest that the induction of tension by carbachol impairs relaxation to VIP. This impairment was so extensive that removal of chloride, which abolished the effects of VIP on body circular muscle (Daniel et al, 1983;, had no further statistically clear effect. A recent report (Thorpy et al, 1986) shows that VIP-induced relaxation of the LOS is accompanied by an increase in cyclic AMP concentrations, whereas that to field stimulation is accompanied by an increase in cyclic GMP; in several tissues carbachol acting at muscarinic receptors causes a decrease in cyclic AMP concentrations and this may explain its ability to oppose the relaxant actions of VIP but not those of field stimulation (Nathanson et al, 1978;Brown & Goldstein, 1986).…”

“…North American opossums (Didelphis marsupialis) were obtained (Singleton, FL, U.S.A.), handled as previously described (Daniel et al, 1983) and killed by intraperitoneal pentobarbitone (100mgkg-1). The oesophagus and proximal stomach were removed and dissected as previously described (Daniel et al, 1983).…”

“…The oesophagus and proximal stomach were removed and dissected as previously described (Daniel et al, 1983). After removal of the mucosa, the LOS was identified by its thickened structure and locus and divided into 2 mm wide strips.…”

“…by increasing the K+-conductance of the smooth muscle cell membrane (Daniel et al, 1983;Jury et al, 1985). In contrast, VIP caused slight or no membrane hyperpolarization accompanied by a decreased membrane conductance, followed by membrane repolarization and membrane oscillations, which triggered action potentials on the depolarizing phase (Daniel et al, 1983;.…”