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  • Title: On the nature of endogenous purines modulating cholinergic neurotransmission in the guinea-pig ileum.
    Author: Wiklund NP, Gustafsson LE.
    Journal: Acta Physiol Scand; 1987 Sep; 131(1):11-8. PubMed ID: 2823530.
    Abstract:
    By means of agonist and enzyme experiments, the relative importance of endogenous adenosine, adenine nucleotides or other purines as modulators of cholinergic neuroeffector transmission in preparations of guinea-pig ileum muscle has been examined. Adenosine, 2-chloroadenosine, AMP, ADP, ATP and AMPPNP reversibly inhibited contractile responses to transmural stimulation of the guinea-pig ileum longitudinal muscle. 5'-adenylate deaminase dose-dependently antagonized the inhibitory effect of adenosine, AMP, ADP, ATP and AMPPNP, but not that of 2-chloroadenosine. 8-p-sulphophenyltheophylline, adenosine deaminase and 5'-adenylate deaminase enhanced contractile responses to transmural nerve stimulation. Adenosine deaminase and 5'-adenylate deaminase were virtually equiactive whereas 8-p-sulphophenyltheophylline was much more effective, and the theophylline derivative also enhanced contractile responses in preparations pretreated with adenosine deaminase or 5'-adenylate deaminase. Moreover, 8-p-sulphophenyltheophylline abolished the inhibition by dipyridamole, whereas adenosine deaminase and 5'-adenylate deaminase only partly antagonized the inhibitory effect of dipyridamole. Application of 5'-adenylate deaminase did not enhance the nerve-induced contractions in preparations pretreated with adenosine deaminase or a combination of dipyridamole and adenosine deaminase. In conclusion, adenosine deaminase and 5'-adenylate deaminase enhanced the nerve-induced contractions in the ileum, and, since 5'-adenylate deaminase was inactive after pretreatment with adenosine deaminase, this suggests that endogenous adenosine rather than 5'-adenine nucleotides modulated cholinergic neurotransmission in the ileum.(ABSTRACT TRUNCATED AT 250 WORDS)
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