Distinct muscarinic receptors, G proteins and phospholipases in esophageal and lower esophageal sphincter circular muscle.
Acetylcholine (ACh)-induced contraction of esophageal circular smooth muscle cells was inhibited by the M2 muscarinic antagonist methoctramine. In lower esophageal sphincter (LES) cells contraction was inhibited by the M3 antagonist p-fluoro-hexa-hydro-sila-difenidol (pF-HSD). Pertussis toxin (PTX) reduced ACh-induced contraction of esophageal but not of LES cells, which suggested that different receptor-linked G proteins are involved. Antibodies against G13 antagonized contraction of esophageal cells and G9-G11 antibodies antagonized contraction of LES cells. The phosphatidylinositol-specific phospholipase C (PLC) inhibitors, U-73122 and neomycin, reduced ACh-induced contraction of LES but not of esophageal cells. Conversely, propranolol and p-chloromercuribenzoic acid (pCMB), which inhibit a phosphatidylcholine-specific phospholipase D (PLD)-dependent pathway, reduced contraction of esophageal but not of LES muscle cells. At 1 and 5 sec after the administration of ACh (10(-5) M), inositol 1,4,5-trisphosphate (IP3) increased only in LES muscle, which suggested that contraction results from PLC-induced IP3 production in the LES but not in the esophagus. The IP3 receptor antagonist heparin, and depletion of intracellular Ca++ stores by thapsigargin or A23187, inhibited ACh-induced contraction of LES but not of esophageal muscle. It was concluded that ACh-induced esophageal contraction depends preferentially on M2 receptors, a PTX-sensitive G13 protein, phosphatidylcholine-specific PLD and production of diacylglycerol (DAG) and is independent of IP3 formation and the release of intracellular Ca++. Conversely, LES contraction is mediated through M3 receptors, a PTX-insensitive G9-G11 protein, activation of PLC, IP3 formation and the release of intracellular Ca++.
Sohn
U D
UD
Department of Medicine, Rhode Island Hospital, Providence.
Harnett
K M
KM
De Petris
G
G
Behar
J
J
Biancani
P
P
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002415:Cats; D004075:Diglycerides / Q000096:biosynthesis; D004789:Enzyme Activation / Q000187:drug effects; D004943:Esophagogastric Junction / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D004947:Esophagus / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D005260:Female; D019204:GTP-Binding Proteins / Q000502:physiology*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000737:chemistry / Q000201:enzymology; D037342:Pertussis Toxin; D010716:Phosphatidylinositols / Q000378:metabolism; D010739:Phospholipase D / Q000378:metabolism; D010740:Phospholipases / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000502:physiology*; D012680:Sensitivity and Specificity; D015398:Signal Transduction / Q000502:physiology*; D010738:Type C Phospholipases / Q000378:metabolism; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D004075:Diglycerides; D010716:Phosphatidylinositols; D011976:Receptors, Muscarinic; D010566:Virulence Factors, Bordetella; D015544:Inositol 1,4,5-Trisphosphate; D037342:Pertussis Toxin; D010740:Phospholipases; D010738:Type C Phospholipases; D010739:Phospholipase D; D019204:GTP-Binding Proteins; D000109:Acetylcholine