Mechanism of action of somatostatin on the canine ileal circular muscle

Abstract

The aim of this study was to investigate the mechanism of action of somatostatin on the circular muscle of the isolated canine ileum using the microelectrode technique. The membrane potential from circular muscle cells was recorded in two preparations: 1) whole thickness circular and longitudinal muscle (with intact myenteric and deep muscular plexuses, n = 13) and 2) isolated circular muscle (with only deep muscular plexus, n = 9). In this preparation, inhibitory junction potentials (IJPs), elicited after field stimulation, are mediated by a nitric oxide-related (NO-R) compound. Somatostatin (10(-6) M) transiently (2-5 min) depolarized the circular muscle cells in both whole thickness (3.6 +/- 1.0 mV, P < 0.01) and isolated circular muscle preparations (8.0 +/- 0.8 mV, P < 0.01). Somatostatin did not reduce either the amplitude or duration of the IJP in the isolated circular muscle but reduced slow-wave amplitude. In contrast, a reduction (20-50%) in the amplitude of the IJP was observed in the whole thickness preparation, and there was little effect on slow-wave amplitude. Somatostatin did not affect the induced slow wave observed in the whole thickness preparation after field stimulation. Apamin significantly reduced the amplitude of the IJP in both preparations. Somatostatin (10(-6) M) did not modify the apamin-resistant IJP. A reduction in the slow-wave amplitude was observed in the isolated circular muscle preparation.(ABSTRACT TRUNCATED AT 250 WORDS)

The ileocolonic sphincter

“…In conscious rabbit, somatostatin increases the pressure necessary to pass fluid through the ICS 75 . This potential increase in tone is in accordance with the depolarizing effect of somatostatin on ileal circular muscle through the inhibition of the release of NO‐related compound 76 …”

Relative contribution of SKCa and TREK1 channels in purinergic and nitrergic neuromuscular transmission in the rat colon

“…Apamin is a pharmacological tool widely used to discriminate between the fast and the slow component of the IJP and even nowadays the term "apamin sensitive" vs. "apamin insensitive" IJP is often used in the literature. Apamin reduces the IJPf in several areas of the gastrointestinal tract and in several species (22,38,39,43,46,49). However, the slow component is also partially reduced by apamin in the human colon (23) and smallconductance calcium-activated potassium channel (SK Ca ) channels might participate in nitrergic neurotransmission in the ileum of the hamster (28) and in the esophagus of the opossum where the junction potential is mainly nitrergic (5).…”

Receptors in interstitial cells of Cajal: Identification and possible physiological roles

“…The presence of Som in the digestive system had been well described (Costa et al, 1980;Ekblad et al, 1988), but contrasting results have been obtained regarding its actions on intestinal smooth muscle. In fact, it has been reported that through activation of inhibitory neurons and/or inhibition of excitatory neurons, Som caused muscle relaxation in guinea-pig intestine in vitro (Furness and Costa 1979), while it inhibited NO release and thereby excited intestine circular muscle in canine ileum in vivo (Jimenez et al, 1995). It has been shown that rat ICC-DMP express a particular subtype of Som receptors, sst 2A , and are surrounded by Som-IR nerve endings (Sternini et al, 1997).…”