dinoprost and phorbol-12-13-diacetate

The pharmacological and biochemical mechanisms of contractile responses to the protein kinase C (PKC) activator phorbol-12,13-diacetate (PDA) were investigated in canine basilar arteries. In the normal medium, PDA elicited a strong, dose-related, and slow-developing sustained contraction. Among the constrictors examined, including serotonin, prostaglandin F2 alpha, and endothelin, only PDA yielded contractions in a Ca2(+)-free medium. In both media, the PDA-induced contractions were virtually inhibited by either staurosporine, H-7, or quinacrine, while neither neurotransmitter blockades nor R24571 (calmidazolium) exerted significant effects. In addition, it was shown that 8-bromocyclic GMP, but not 8-bromocyclic AMP, markedly curtailed the PDA-induced contractions. Biochemical analysis, furthermore, showed that PDA induced increased phosphorylations of 27- and 96-kDa and proteins other than the myosin light chain (MLC) 20-kDa protein. Thus, the present results open up a novel mechanism of sustained cerebral artery contractions, where PKC activation rather than Ca2+/calmodulin/MLC system plays a key role that is regulated both by phospholipase A2 and by cyclic GMP.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; Alkaloids; Animals; Basilar Artery; Cyclic GMP; Dinoprost; Dogs; Endothelins; Enzyme Activation; Female; Imidazoles; Isoquinolines; Male; Muscle Contraction; Phorbol Esters; Phosphorylation; Piperazines; Protein Kinase C; Quinacrine; Serotonin; Staurosporine

We previously suggested that activation of the protein kinase C-mediated contractile system may participate in the occurrence of chronic cerebral vasospasm. In the present study, we compared segments of normal beagle basilar arteries in vitro with segments of arteries undergoing chronic vasospasm to determine the responsiveness to various agonists such as serotonin, prostaglandin F2 alpha, and phorbol 12,13-diacetate as well as to external Ca2+. We also compared the effects of W-7 (a calmodulin inhibitor), nicardipine (a calcium channel blocker), and H-7 (a protein kinase C inhibitor) on the spontaneous tonus of arterial segments stabilized at a resting tension of 3 g. Compared with normal segments, the responsiveness to each agonist in segments undergoing vasospasm was essentially unchanged whereas the the responsiveness to external Ca2+ was significantly decreased (p less than 0.001). In segments undergoing vasospasm the decrease in resting tension induced by W-7 was markedly diminished (p less than 0.01), that induced by nicardipine was unchanged, and that induced by H-7 was significantly increased (p less than 0.01). Our results indicate that spontaneous tonus due to activation of the protein kinase C system is significantly augmented in segments undergoing vasospasm. Thus this system, rather than the Ca2+/calmodulin system, appears to play a major role in the occurrence of chronic vasospasm.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; Animals; Basilar Artery; Chronic Disease; Dinoprost; Dogs; Enzyme Activation; In Vitro Techniques; Ischemic Attack, Transient; Isoquinolines; Muscle Contraction; Muscle, Smooth, Vascular; Nicardipine; Phorbol Esters; Piperazines; Protein Kinase C; Protein Kinase Inhibitors; Serotonin; Subarachnoid Hemorrhage; Sulfonamides