Purinergic modulation of spontaneous activity and of responses to high potassium and acetylcholine in rat ileal smooth muscle.

Abstract

1. In rat ileal smooth muscle both adenosine and ATP at 10(-4) M significantly enhanced spontaneous mechanical activity. The excitatory actions of adenosine were blocked by the P1 receptor antagonist 8-phenyltheophylline and the excitatory effects of ATP were significantly reduced by the P2 receptor antagonist quinidine. 2. The P2 receptor desensitizer alpha,beta-methylene-ATP was without effect on ACh responses nor did the stable analogue beta,gamma-methylene-ATP exert any effect on spontaneous mechanical activity. 3. Pretreatment with adenosine caused a dose-dependent enhancement of K-induced contractures in the ileum. Low adenosine concentrations slightly inhibited and high concentrations slightly enhanced ACh-induced contractures in the ileum. 4. ATP potentiated the phasic component of the ileal K-induced contracture but strongly inhibited tonic force at high concentrations. This agent slightly inhibited the phasic component of the ACh-induced contracture while strongly inhibiting ACh-induced tonic force. 5. alpha,beta-methylene-ATP inhibited ileal muscle ACh induced contractures while it potentiated both phasic and tonic K-induced contractures. beta,gamma-methylene ATP inhibited ACh-induced contractures but it enhanced K-induced phasic contractures while inhibiting K-induced tonic force. 6. The results of this study suggest that rat ileum may contain the A1 subtype of the P1 receptor but the evidence for a P2 receptor subtype is conflicting despite the inhibition of ATP actions by quinidine. 7. The inhibition of K- and ACh-induced tonic force suggests that adenosine and ATP interactions with ileal smooth muscle may inactivate slow voltage-dependent calcium channels leading to EC uncoupling.

• Authors: S M Mahmod, H Huddart
• Journal: Comparative biochemistry and physiology. C, Comparative pharmacology and toxicology (Comp Biochem Physiol C Comp Pharmacol Toxicol) Vol. 106 Issue 1 Pg. 79-85 (Sep 1993) ISSN: 0742-8413 [Print] England
• PMID: 7903624 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Receptors, Purinergic
• Adenosine Triphosphate
• Adenosine
• Acetylcholine
• Potassium

Topics

• Acetylcholine (pharmacology)
• Adenosine (pharmacology)
• Adenosine Triphosphate (analogs & derivatives, pharmacology)
• Animals
• Ileum (drug effects, physiology)
• Male
• Muscle Contraction
• Muscle, Smooth (drug effects, physiology)
• Potassium (pharmacology)
• Rats
• Rats, Wistar
• Receptors, Purinergic (drug effects)