Regulation Of P2 Receptors On Motility Of Gastrointestinal Smooth Muscle In The Rat

Objective: To observe the modulation of adenosinetriphosphate (ATP) on motility of isolated gastric smoothmuscle in the rat, and effects of ATP on longitudinal musclestrips isolated from the rat proximal colon and the receptorsinvolved in the effects. The contractile effects of ATP werestudied in circular muscle strips of the rat gastric body tocharacterize the receptors involved.Methods: Longitudinal and circular muscle strips of the ratgastric body and antrum were prepared, and the effects of ATPon the motility of the strips were investigated. Relaxant andcontractile responses to ATP and adenosine in longitudinalmuscle strips of the rat proximal colon were observed. Theeffects of ATP, α,β-methyleneATP and adenosine on circularmuscle strips of the rat gastric body were investigated tocharacterize the receptors involved.Results: ATP (0.1 μmol·L^-1 -1 mmol·L^-1) induced a smallrelaxation followed by an obvious spasm in longitudinal musclestrips of the gastric body, and induced a larger relaxationfollowed by a smaller spasm in the preparation pre-contractedby KCl.ATP (0.1 μmol·L^-1 -1 mmol·L^-1) only producedcontraction in circular muscle strips of the gastric body.Lowconcentration of ATP (1 μmol·L^-1 -100 μmol·L^-1) inhibited thecontractile amplitude of the antral longitudinal strips, increasedthe frequency of the contraction apparently, and it producedconcentration-related relaxation when the preparation waspre-contracted by KCl.Low concentration of ATP (1 μmol·L^-1-10 μmol·L^-1) firstly enhanced and then inhibited contractileamplitude of antral circular musle strips, while highconcentration of ATP (100 μmol·L^-1 -1 mmol·L^-1) fullyinhibited the motility.ATP (0.1 μmol·L^-1 -1 mmol·L^-1) produced a weakrelaxation followed by a concentration-dependent contractileresponse in longitudinal muscle strips of the rat proximal colonat resting tension, and tetrodotoxin (TTX, 0.1 μmol·L^-1) did notinfluence the responses to ATP (100 μmol·L^-1). Adenosine (1μmol·L^-1 -100 μmol·L^-1) did not produce an obviouslycontractile response in the preparation at resting tension.When the preparations were precontracted with5-hydroxytryptamine(1 μmol ·L^-1) or acetylcholine(0.3μmol·L^-1), ATP produced obviously relaxant responses in aconcentration-dependent manner, however the relaxant responseto adenosine was much weaker than that to ATP.ATP (0.1 μmol·L^-1 -300 μmol·L^-1) and α,β-MeATP(0.1 μmol·L^-1 -30 μmol·L^-1) produced concentration -dependent contractile responses in circular muscle strips of therat gastric body, and the contractile response to α,β-MeATPwas much weaker than that to ATP, while adenosine produced a...