Pulmonary artery vasoconstriction but not [Ca2+]i signal stimulated by thromboxane A2 is partially resistant to NO.

Abstract

To characterize the thromboxane A2 (TXA2) -induced resistance to the vasodilator effects of the nitric oxide (NO)/cGMP pathway in pulmonary arteries, we have studied the effects of the NO donor sodium nitroprusside on intracellular calcium concentration ([Ca2+]i) and contractile force recorded simultaneously in isolated piglet pulmonary arteries loaded with fura-2 and contracted with norepinephrine or the TXA2 mimetic U46619 and by activation of protein kinase C (PKC) with phorbol 12-myristate 13-acetate. In the TXA2 mimetic- and phorbol 12-myristate 13-acetate plus norepinephrine-stimulated arteries, nitroprusside exhibited lower vasodilator efficacy (and lower potency in the TXA2 mimetic-stimulated arteries) but similar reductions in [Ca2+]i compared with arteries activated by norepinephrine. The nonselective serine/threonine kinase inhibitor staurosporine, but not the selective inhibitor of PKC bisindolylmaleimide, potentiated the relaxation of nitroprusside in the TXA2 mimetic-stimulated arteries. In conclusion, the resistance to NO/cGMP-induced vasodilation in arteries stimulated by TXA2 and PKC involves a reduced ability of the Ca2+-independent mechanisms for smooth muscle vasodilation. The resistance to NO in arteries stimulated by TXA2 is sensitive to staurosporine but not to bisindolylmaleimide, suggesting the involvement of an activation of a serine/threonine kinase distinct from PKC.