The Sources of Ca2+ for Muscarinic Receptor-induced Contraction in the Rat Ileum

Abstract

The contractile responses obtained by activation of different muscarinic receptor subtypes in the longitudinal muscle of the rat ileum and especially the responses of this muscle to acetylcholine in a Ca(2+)-free medium have been investigated. In Ca(2+)-containing solution, acetylcholine elicited similar concentration-dependent contractile responses in the duodenum, jejunum and ileum strips of the rat intestine. The response to a maximal concentration of the agonist (1 microM) consisted of a rapid phasic response followed by a slower tonic one. Nifedipine completely relaxes or inhibits the sustained response and only partially diminishes the phasic one, which suggests that the phasic contraction depends on the release of internal Ca2+ entry from the extracellular space through voltage-dependent Ca2+ channels, but that the tonic contraction only depends on the influx of the external ion. In Ca(2+)-free medium, acetylcholine (1 microM) induced phasic contractions that depend on the release of this ion from internal stores. Participation of different subtypes of receptors (M1, M2 and M3) in these responses depends on the inhibitory action shown by methoctramine, 4-DAMP and atropine but not by pirenzepine in two different experimental models.

Origin of Ca2+ Necessary for Carbachol-Induced Contraction in Longitudinal Muscle of the Proximal Colon of Rats

“…In the Ca 2+ -free bathing solution, CCh induced only a phasic contraction that was probably induced by the release of Ca 2+ from the intracellular store, SR in the fundus strips (12) and duodenum (13) of rats and circular muscle of the fundus strip of guinea pigs (14), whereas it did not induce any contraction in longitudinal muscle of guinea pig ileum (11). In rat ileal longitudinal muscle, ACh induced phasic contraction by the Ca 2+ influx through voltage-dependent Ca 2+ channels (8). Some reports on the Ca 2+ source for the tonic phase of the contraction are also inconsistent with each other.…”

“…On the other hand, a high potassium concentration increases [Ca 2+ ] i only by opening of voltage-dependent Ca 2+ channels (1). Acetylcholine (ACh) or a muscarinic agonist, carbachol (CCh), was shown to elicit contraction consisting of a rapid phasic phase followed by a tonic one by activation of M3 muscarinic receptors in the rat gastric fundus (6), duodenum (7) and ileum (8); the guinea pig gastric fundus (9) and ileum (10,11); and the human ileum (11). However, there are some different reports concerning the source of Ca 2+ for the muscarinic receptor-mediated contraction.…”

Effect of a crude sulfated polysaccharide from Halymenia floresia (Rhodophyta) on gastrointestinal smooth muscle contractility

“…In this regard, it was observed that in Ca 2+ -containing solution, acetylcholine elicited similar concentration-dependent contractile responses in the duodenum, jejunum, and ileum strips of rat intestine. However, in Ca 2+ -free medium, acetylcholine induced phasic contractions that depended on the release of this ion from internal stores by the activation of the sarcoplasmatic-operated Ca 2+ channels (Elorriaga et al, 1996). Gastric emptying results from the integrated contractions of the proximal stomach, distal stomach, pylorus, and duodenum (Wingate et al, 1994).…”

Sources of calcium in agonist-induced contraction of rat distal colon smooth muscle in vitro

“…ACh has been shown to elicit contraction that consists of a rapid phasic phase, followed by a tonic phase, by activation of M3 muscarinic receptors in the rat and guinea pig gastric fundus and ileum, and the human ileum [16][17][18][19] . However, there have been some different results concerning the source of Ca 2+ for muscarinic receptormediated contraction.…”