Distinct muscarinic receptors and signal transduction pathways in gallbladder muscle.
Acetylcholine (ACh) caused a dose-dependent contraction of gallbladder muscle cells in either a normal (1.9 mM) Ca2+, zero-Ca2+ or 4 mM Sr2+ medium, with a maximal contraction about 21 +/- 1% at 10(-6) M. Pirenzepine, methoctramine and p-fluoro-hexahydro-sila-difenidol (the M1, M2 and M3 antagonist, respectively) alone had no inhibitory effect on ACh-induced contraction in normal Ca2+ medium, which was blocked by the combination of methoctramine and p-F-HHSiD. In the 4 mM Sr2+ medium, methoctramine dose dependently inhibited ACh-induced contraction and shifted the ACh dose-response curve to the right. The contraction induced by ACh was further blocked by 10(-4) M propranolol (phosphatidic acid phosphohydrolase inhibitor that prevents the production of diacylglycerol from phospholipase D activation), 10(-5) M H-7 and chelerythrine (the protein kinase C inhibitors) by 64%, 75% and 77%, respectively. In contrast, in the zero-Ca2+ medium, p-fluoro-hexahydro-sila-difenidol dose-dependently inhibited ACh-induced contraction and shifted the ACh dose-response curve to the right. The action of ACh was further blocked by 10(-6) M U-73122 (phospholipase C inhibitor) and 10(-5) M CGS 9343B (calmodulin antagonist) by 95% and 77%, respectively. In conclusion, ACh contracts the gallbladder muscle by stimulating the M2 and M3 muscarinic receptors. The M2 receptors are linked to Ca2+ influx, activation of phospholipase D and protein kinase C-dependent pathway, whereas the M3 receptors are preferentially associated with the activation of phospholipase C, intracellular Ca2+ release and calmodulin-dependent pathway.
Chen
Q
Q
Department of Medicine, Rhode Island Hospital, Providence, USA.
Yu
P
P
de Petris
G
G
Biancani
P
P
Behar
J
J
D000109:Acetylcholine / Q000378:metabolism / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002415:Cats; D005260:Female; D005704:Gallbladder / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction
D011976:Receptors, Muscarinic; D000109:Acetylcholine; D002118:Calcium