EFFECTS OF CYCLOPIAZONIC ACID ON CONTRACTILITY AND ECTO-ATPASE ACTIVITY IN GUINEA-PIG URINARY-BLADDER AND VAS-DEFERENS

1 Cyclopiazonic acid (CPA), an inhibitor of sarcoplasmic ATPase, was t ested on guinea-pig urinary bladder and vas deferens for its ability: (1) to modify contractile responses to electrical field stimulation (E FS), exogenous ATP, alpha,beta-methylene ATP (alpha,beta-meATP), carba chol, noradrenaline (NA), histamine, and KCl; (2) to affect ecto-ATPas e activity; (3) to modify the release of ATP evoked by EFS. 2 In the u rinary bladder, CPA (10 mu M) potentiated contractile responses to EFS , exogenous ATP (100 mu M), alpha,beta-meATP (1 mu M), carbachol (0.5 mu M), histamine (30 mu M) and KCl (30 mM). In the vas deferens, CPA ( 10 mu M) potentiated responses to EFS, ATP, alpha,beta-meATP, NA (100 mu M) and KCl. CPA at a concentration of 1 mu M had no effect on ATP-i nduced relaxation of carbachol-precontracted guinea-pig taenia coli, a nd at a concentration of 10 mu M it markedly increased spontaneous con tractile activity of taenia. 3 Ecto-ATPase was estimated to have V-max and K-m values of 0.98 nmol P-i 30 min(-1) mg(-1) wet tissue and 881 mu M ATP in the urinary bladder, and 0.75 nmol P-i 30 min(-1) mg(-1) w et tissue and 914 mu M ATP in the vas deferens, respectively. CPA at a concentration of 10 mu M significantly inhibited ecto-ATPase activity by 18% in the urinary bladder and by 24% in the vas deferens. 4 In th e guinea-pig vas deferens, CPA significantly potentiated ATP release e voked by EFS from 2.2 +/- 0.8 (6) pmol ATP min(-1) g(-1) wet tissue to 35.2 +/- 4.8 (6) pmol ATP min(-1) g(-1) wet tissue (P < 0.01). 5 In c onclusion, the potentiation of contractile responses of the guinea-pig urinary bladder and vas deferens by CPA has a non-specific character. CPA inhibited ecto-ATPase activity and increased ATP release, but the se effects do not appear to contribute to the potentiation of P-2x-pur inoceptor-mediated responses since the contractile actions of all the agonists studied were potentiated to the same extent.