Superoxide anion stress attenuates the contractile response of the guinea pig vas deferens to ATP and diadenosine tetraphosphate

Induction of endogenous superoxide anion stress by the use of the superoxide dismutase inhibitor diethylthiocarbamate (DETCA; 10 mmol/l) produced a potent inhibition of the ATP (0.3-10 mmol/l) and diadenosine tetraphosphate (AP(4)A) contractile activity in the isolated vas deferens by 29-92 and 24-90%, respectively. Pyrogallol (0.1 mmol/l), the exogenous superoxide anion generator, produced a significant inhibition on the contractile activity of the vas deferens induced by ATP and AP(4)A by 33-89 and 25-82%, respectively. DETCA (10 mmol/l) and pyrogallol (0.1 mmol/l) attenuated the contractile response of isolated guinea pig vas deferens strips to the selective P2X agonist alpha,beta-methyleneATP (alpha,beta-meATP; 50 mu mol/l) by 25 and 47%, respectively. In Ca2+-free high-K+ (80 mmol/l) Krebs solution, pyrogallol and DETCA produced inhibition of the contractile response to alpha,beta-meATP (50 mu mol/l) in similar way to that in normal Krebs solution. The further addition of CaCl2 (1 mmol/l) abolished the inhibitory effects exerted by pyrogallol and DETCA. The control contractile response to alpha,beta-meATP (50 mu mol/l) was not affected in Ca2+-free high-K+ (80 mmol/l) Krebs solution. It may be concluded that superoxide anion stress produces a significant inhibitory effect on both mono-and di-nucleotide purinergic contraction of the vas deferens. Superoxide anion appears to interrupt the P2X(1)-mediated transduction cascade at some step(s) of intracellular calcium handlin