Activation of the protein kinase C-mediated contractile system in canine basilar artery undergoing chronic vasospasm.

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.