['Current treatments for conduit vessel vasospasm are short-acting and do not inhibit all vasospastic stimuli. This study tests the hypothesis that irreversible inactivation of myosin light chain kinase provides sustained inhibition of arterial vasoconstriction stimulated by a spectrum of vasopressors.', 'Canine radial artery segments were soaked for 60 min in control buffer or buffer with wortmannin, an irreversible inhibitor of myosin light chain kinase. The vessels were then thoroughly washed and contractile responses were quantified in response to a spectrum of vasopressors at 2 and 48 h after treatment. After 48 h, selected vessels were examined for morphologic changes and development of apoptosis.', 'Two hours after treatment, wortmannin-soaked vessels contracted significantly less than controls in response to norepinephrine (0.19+/-0.07 g vs. 7.22+/-0.37 g, P<0.001), serotonin (0.92+/-0.35 g vs. 9.64+/-0.67 g, P<0.001), thromboxane-mimetic U46619 (1.25+/-0.17 g vs. 10.99+/-0.50 g, P<0.001), and KCl (1.98+/-0.27 g vs.15.00+/-0.48 g, P<0.001). At 48 h, vasoconstriction remained significantly inhibited in wortmannin-treated vessels compared to control vessels in response to norepinephrine (2.36+/-0.17 vs. 6.95+/-0.47 g, P<0.001), serotonin (4.67+/-0.39 vs. 12.42+/-0.70 g, P<0.001), U46619 (5.42+/-0.34 vs. 9.29+/-0.74 g, P=0.008), and KCl (7.49+/-0.48 vs. 13.32+/-0.60 g, P<0.001). Histology of wortmannin-treated vessels revealed no overt smooth muscle or endothelial cell damage. TUNEL staining revealed a significantly greater proportion of apoptotic smooth muscle and endothelial cells in wortmannin-treated vessels as compared to controls.'] Does inhibition of myosin light chain kinase provide prolonged attenuation of radial artery vasospasm?