Pharmacological effects of L-AMP-PCP on ATP receptors in smooth muscle.

The pharmacological effects of ATP and of two of its analogues, AMP-PCP and L-AMP-PCP, were investigated in various isolated smooth muscle preparations. In the guinea-pig vas deferens, the rat portal vein and the rat anococcygeus the nucleotides all caused contraction, and the order of potency was L-AMP-PCP greater than AMP-PCP greater than ATP. In the guinea-pig field-stimulated ileal longitudinal muscle the nucleotides all inhibited the contractions, and the order of potency was ATP greater than AMP-PCP greater than L-AMP-PCP. In the guinea-pig thoracic aorta ATP and AMP-PCP caused relaxations, ATP being more potent than AMP-PCP, and L-AMP-PCP caused contractions. These results are consistent with the suggestion that the ATP receptors mediating contraction of smooth muscle are different from those mediating relaxation, and show that L-AMP-PCP is a potent, specific agonist at excitatory ATP receptors.