Characterization of muscarinic receptors on guinea pig gallbladder smooth muscle.
BACKGROUND
Cholinergic agonists are of major importance for the regulation of gallbladder motility. However, the gallbladder muscarinic receptors have not been localized or characterized directly using radioligands, and it has not been clearly established which subtype of muscarinic receptor mediates contraction. The aim of the present study was to characterize the gallbladder muscarinic receptors.


METHODS
Binding studies to guinea pig gallbladder sections were performed using 1-[N-methyl-3H] scopolamine methyl chloride. Carbachol-induced contraction was measured using muscle strips.


RESULTS
Binding of 1-[N-methyl-3H] scopolamine methyl chloride was reversible, dependent on time, temperature, and pH. Autoradiography showed binding only over the smooth muscle. Binding and carbachol-induced contractions were inhibited by muscarinic receptor antagonists with the following potencies: atropine > N-methyl-scopolamine > silahexocyclium-methylsulfate > AF-DX 384 [(+-)-5,11-dihydro-11-([(2-(2-[(dipropylamino)-methyl]-1- piperidinyl)ethyl)amino]carbonyl)-6H-pyrido (2,3b) (1,4)-benzodiazepine-6-one] > hexahydro-siladifenidol hydrochloride > AF-DX 116 [(+-)-11-([2-[(diethylamino)methyl]-1- piperidinyl]-acetyl)-5,11-dihydro-6H-pyrido (2,3b)(1,4)benzodiazepine-6-one] > pirenzepine. Carbachol inhibited binding to gallbladder sections over the same range of concentrations that caused contractions. The concentration-contraction curves for carbachol were not altered by tetrodotoxin.


CONCLUSIONS
Gallbladder smooth muscle cells possess muscarinic receptors of the M3 type. These receptors mediate carbachol-induced contraction.
von Schrenck
T
T
Department of Medicine, University Hospital Eppendorf, Hamburg, Germany.
Sievers
J
J
Mirau
S
S
Raedler
A
A
Greten
H
H
D000818:Animals; D001345:Autoradiography; D002217:Carbachol / Q000494:pharmacology; D005704:Gallbladder / Q000737:chemistry* / Q000187:drug effects / Q000502:physiology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000737:chemistry* / Q000502:physiology; D019832:N-Methylscopolamine; D010890:Pirenzepine / Q000031:analogs & derivatives / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000032:analysis* / Q000502:physiology; D012602:Scopolamine Derivatives / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology
D011976:Receptors, Muscarinic; D012602:Scopolamine Derivatives; D010890:Pirenzepine; D013779:Tetrodotoxin; D002217:Carbachol; C048593:otenzepad; D019832:N-Methylscopolamine