Five subtypes of muscarinic receptors are expressed in gastric smooth muscles of guinea pig.
Muscarinic receptors play key roles in the control of gastrointestinal smooth muscle activity. However, specific physiological functions of each subtype remain to be determined. In this study, the nonselective cation channel activated by carbachol (I(CCh)) was examined in circular smooth muscle cells of the guinea pig gastric antrum using patch-clamp technique. 4-DAMP inhibited I(CCh) dose-dependently with IC(50) of 1.1 0.1 nM (n = 6). GTPgS-induced current, however, was not inhibited by 10 nM 4-DAMP. I(CCh) was not recorded in pertussis-toxin (PTX)-pretreated smooth muscle cells of gastric antrum. I(CCh) values in response to 10 mM CCh at a holding potential of 60 mV were -330 32 pA (n=4) and -15 3 pA (n = 6) in the control and PTX-treated cells, respectively (P 0.01). Sensitivities to nanomolar 4-DAMP and PTX suggest the possible involvement of m4 subtype. Using sequence information obtained from cloned guinea pig muscarinic receptor genes, it is possible to amplify the cDNAs encoding m1-m5 from guinea pig brain tissue. Single cell RT-PCR experiments showed that all five subtypes of muscarinic receptor were present in circular smooth muscle cells of the guinea pig gastric antrum. Together with our previous results showing that G(o) protein is important for activation of ACh-activated NSC channels, our results suggest that I(CCh) might be activated by acetylcholine through m4 subtype as well as m2 and m3 subtypes in guinea-pig stomach.
So
Insuk
I
Department of Physiology and Biophysics, College of Medicine, Seoul National University, Seoul 110-799, Korea.
Yang
Dong Ki
DK
Kim
Hyun Jin
HJ
Min
Kyung Wan
KW
Kang
Tong Mook
TM
Kim
Sung Joon
SJ
Kim
Ki Whan
KW
Park
Ki Ho
KH
Jeon
Ju-Hong
JH
Choi
Kyung-Ho
KH
Kim
In-Gyu
IG
D000818:Animals; D001483:Base Sequence; D002217:Carbachol / Q000494:pharmacology; D002412:Cations; D018679:Cholinergic Agonists / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005753:Gastric Mucosa / Q000378:metabolism*; D006168:Guinea Pigs; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D010880:Piperidines / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000737:chemistry / Q000145:classification / Q000378:metabolism*; D013270:Stomach / Q000187:drug effects
D002412:Cations; D018679:Cholinergic Agonists; D007473:Ion Channels; D018727:Muscarinic Antagonists; D010880:Piperidines; D011976:Receptors, Muscarinic; C042375:4-diphenylacetoxy-1,1-dimethylpiperidinium; D002217:Carbachol