Subtypes of muscarinic receptors regulating gallbladder cholinergic contractions

Abstract

The aim of this study was to determine the functional role of muscarinic receptor subtypes regulating gallbladder cholinergic contractions. Electrical field stimulation (EFS; 16 Hz) produced contractile responses of guinea pig gallbladder muscle strips in vitro that were inhibited by 1 μM tetrodotoxin (2 ± 2% of control) and 1 μM atropine (1 ± 1% of control), indicating activation of intrinsic cholinergic nerves. Exogenous ACh (5 μM)-induced contractions were inhibited by atropine (1 ± 1% of control) but not tetrodotoxin (102 ± 1% of control), indicating a direct effect on smooth muscle. The M1 receptor antagonist pirenzepine (10 nM) had no effect on ACh-induced contractions but inhibited EFS-induced contractions by 11 ± 3%. The M2 antagonist methoctramine (10 nM) had no effect on ACh-induced contractions but augmented EFS-induced contractions by 5 ± 2%. The M3 antagonist 4-DAMP (10 nM) inhibited ACh-induced contractions by 14 ± 4% and EFS-induced contractions by 22 ± 5%. In conclusion, specific M1, M2, and M3 receptors modulate gallbladder muscle contractions by regulating ACh release from cholinergic nerves and mediating the contraction. Cholinergic contractions are mediated by M3 receptors directly on the smooth muscle. M2 receptors are on cholinergic nerves and function as prejunctional inhibitory autoreceptors. M1 receptors are on cholinergic nerves and function as prejunctional facilitatory autoreceptors.

Muscarinic Receptor Knockout Mice: Role of Muscarinic Acetylcholine Receptors M2, M3, and M4 in Carbamylcholine-Induced Gallbladder Contractility

“…M 1 , M 2 , M 3 , and M 4 muscarinic receptors have been implicated in the contractile response to muscarinic agonists in gallbladder (Parkman et al, 1999). In addition, M 1 , M 2 , M 3 , and M 4 receptor mRNA exists in human gallbladder, again raising the possibility that each of these receptors may be involved in the cholinergically mediated contractile response of gallbladder (Heinig et al, 1997).…”

“…In fact, multiple studies using pharmacological tools have implicated a role for M 3 receptors on gallbladder contractility in guinea pig (von Schrenck et al, 1993;Takahashi et al, 1994;Eltze et al, 1997) and cat (Chen et al, 1995). In addition, M 2 receptor activation has been linked to contractility in the cat (Chen et al, 1995) and guinea pig gallbladder (Oktay et al, 1998), although this receptor may serve as an inhibitory presynaptic autoreceptor in guinea pig gallbladder (Parkman et al, 1999) rather than possessing a direct role in gallbladder smooth muscle contractility . The possibility of a prominent role for M 3 and a more modest role for M 2 receptors in muscarinic-induced contraction of gallbladder is consistent with previous observations documenting a similar role for these receptors in carbamylcholine-induced contraction of other smooth muscles such as mouse trachea, stomach fundus, and urinary bladder (Stengel et al, 2000).…”

“…Furthermore, unlike the guinea pig gallbladder that possesses an extensive intramural neuronal network (Sutherland, 1967;Yoshida and Tsuruta, 1988;Parkman et al, 1999), gallbladder from the mouse does not possess such an extensive neuronal network Koeda, 1991, 1992). Thus, use of the M 2 , M 3 , and M 4 muscarinic knockout mice can permit a detailed evaluation of the role of these muscarinic receptors in gallbladder smooth muscle contraction.…”

Regional gastric contractility alterations in a diabetic gastroparesis mouse model: effects of cholinergic and serotoninergic stimulation

“…Thus the muscarinic receptor subtypes mediating cholinergic contractions were investigated in this study by determining the inhibitory effects of specific muscarinic receptor subtype antagonists on bethanechol-induced contractions. The M 1 muscarinic subtype receptor antagonist pirenzepine, the M2 antagonist methoctramine, and the M3 antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) (Sigma, St. Louis, MO) were used (27). After an initial control contractile response to 10 M bethanechol followed by rinsing, a 10 nM concentration of receptor antagonist was added, followed in 10 min by the addition of another application of 10 M bethanechol.…”

Effects of Melatonin on Gallbladder Neuromuscular Function in Acute Cholecystitis

“…The neural control of gallbladder motility involves reflexes that include both efferent and afferent nerve fibers as well as the intrinsic plexus in the gallbladder wall (Mawe et al, 2006). Acetylcholine (ACh) released from cholinergic neurons induces contraction of the gallbladder smooth muscle through muscarinic receptors (Parkman et al, 1999b), and it has neuromodulatory functions, promoting or inhibiting the release of other neurotransmitters (Parkman et al, 1999b). Cholinergic neurons coexpress other neurotransmitters such as NO and several neuropeptides (Talmage et al, 1992).…”