Signal transduction mechanism via adenosine Al receptor in the cat esophageal smooth muscle cells

We investigated what adenosine receptor type exists and the signaling pathways on the contraction of circular muscle cells isolated by enzymatic digestion from the cat esophagus. Adenosine or the selective A1 receptor agonist R-PIA causes a concentration-dependent contraction. After pretreatment with A I receptor antagonist, DPCPX, adenosine-mediated contraction was abolished. Adenosine-induced contraction was significantly increased when A1 receptors were preserved by pretreatment with DPCPX followed by inactivation of all unprotected receptors with N-ethylmaleimide. Adenosine- or R-PIA-induced contraction was significantly augmented in the preserved cells and the increase was abolished in the presence of the A1 receptor antagonist DPCPX. PTX abolished contraction induced by adenosine or R-PIA, implying that contraction activated by A1 receptor was coupled to a pertussis toxin (PTX)-sensitive G(i) protein. After permeabilization, contraction was inhibited by G(i2), but not by G(i1) and G(i3), antibodies. These data suggest that adenosine-induced contraction of esophagus depends on PTX-sensitive G(i2), Adenosine- or R-PIA-induced contraction of esophageal smooth muscle cells was not affected by the phospholipase D (PLD) inhibitor rho-chloromercuribenzoic acid (rhoCMB), phospholipase A(2) (PLA(2)) inhibitor DEDA or PKC antagonist chelerythrine, but was significantly abolished by phospholipase C (PLC) inhibitor, neomycin. PLC-beta3 antibody inhibited R-PIA-induced contraction. R-PIA-induced contraction of esophageal muscle cells was inhibited by IP3 receptor antagonist heparin, which suggests that the contraction of esophageal smooth muscle cells is dependent on phosphatidylinositol-specific phospholipase (PI-PLC) and IP3. In conclusion, adenosine- and R-PIA-induced contraction in cat esophageal smooth muscle cell was mediated by A1 receptor. A1 receptor is coupled to PTX-sensitive G protein Gi2, which results in the activation of PI-PLC-beta3. PI hydrolysis by PI-PLC Forms IP3, which binds to IP3 receptor on endoplasmic reticulum, resulting in the release of intracellular Ca2+. (C) 2002 Elsevier Science Inc. All rights reserved.