Contractile responses of chicken rectum to stimulation of Remak's nerve or purinoceptors: effect of suramin.

Stimulation of Remak's nerve produced a rapid contraction of the rectal muscle which was resistant to blockade by hyoscine, followed by a slow contractile response which was cholinergic. With hyoscine (1 microM) in the Tyrode solution, the non-cholinergic contractile response to nerve stimulation was compared with the responses to adenosine triphosphate (ATP) and alpha,beta-methylene adenosine triphosphate (alpha,beta-Me ATP). In the presence of suramin (300 microM), the contractile response to ATP was increased by about 100%, whereas that to nerve stimulation was inhibited by approximately 17%. Suramin (60 microM) also discriminated between the contractile responses to ATP and nerve stimulation, only the former being potentiated by the drug. It seems probable that suramin potentiated the action of ATP in the rectum through inhibition of ectonucleotidase activity. If so, the potentiation should not extend to alpha,beta-Me ATP, as this analogue of ATP is resistant to inactivation by the enzyme. Suramin inhibited the contractile response to alpha,beta-Me ATP. Thus the neurotransmitter which mediated the hyoscine-resistant contractile response to stimulation of Remak's nerve was dissimilar to ATP, in that it was not potentiated by suramin and presumably was not inactivated by ectonucleotidase activity.