ucn-1028-c and Ischemic-Attack--Transient

Although phorbol esters, synthetic activators of protein kinase C (PKC), can stimulate large increases in the binding of cytosolic PKC to form membrane-bound PKC (PKCm, an indicator of PKC activation), the authors report that even small increases in PKCm induced by phorbol esters (8-12% of total PKC content) can be associated with significant PKC-mediated contractions in vitro (50-85% of maximum) in normal canine cerebral arteries. Increases in PKCm of similarly small magnitude were found in vitro when control artery segments were exposed to hemolysate, but only if the arterial smooth-muscle cells were first slightly depolarized by increased extracellular potassium to values of membrane potential similar to those observed in canine cerebral arteries during chronic cerebral vasospasm. These increases in PKCm (6-8% of total PKC content) coincided with a greatly augmented contractile response to hemolysate. These results show that the previous observation of only a small increase in PKCm (approximately 7% of total PKC content) after experimental subarachnoid hemorrhage in the canine model does not preclude a potentially important role for PKC-mediated contraction in the pathogenesis of cerebral vasospasm.

Topics: Animals; Cell Membrane; Cerebral Arteries; Chronic Disease; Cytosol; Dogs; Endothelin-1; Enzyme Activation; Enzyme Inhibitors; Hemolysis; Ischemic Attack, Transient; Membrane Potentials; Muscle, Smooth, Vascular; Naphthalenes; Phorbol 12,13-Dibutyrate; Phorbol Esters; Potassium; Protein Binding; Protein Kinase C; Stress, Mechanical; Subarachnoid Hemorrhage; Vasoconstriction; Vasoconstrictor Agents

Vasospasm was produced in adult mongrel dogs by a two-hemorrhage method, and the spastic basilar arteries were exposed via the transclival route on Day 7. Tonic contraction was produced in the normal canine basilar arteries by a local application of KCl or serotonin after transclival exposure. The exposed spastic and tonic basilar arteries then received a topical application of the following: 1-(5-isoquinolinesulfonyl)-2-methyl-piperazine (H-7), a potent inhibitor of protein kinase C acting at the catalytic domain; calphostin C, a specific inhibitor of protein kinase C acting at the regulatory domain; or calpeptin, a selective inhibitor of calpain. Both spastic and tonic basilar arteries were effectively dilated by H-7. Calphostin C caused only slight dilation of spastic basilar arteries but moderate dilation of tonic basilar arteries. Dilation in response to calpeptin was remarkable in the spastic basilar arteries but slight in the tonic basilar arteries. The doses of calphostin C and calpeptin required to obtain maximum effect were markedly lower in the tonic model than in the spastic model. The spastic and tonic models had a similar dose-dependent response to H-7 but quite a different response to calphostin C or calpeptin, suggesting a difference in the function of protein kinase C and calpain in the two models. Furthermore, the effect of calphostin C on the reversal of vasospasm was increased significantly after topical treatment with calpeptin. It is suggested that the majority of the catalytic domain of protein kinase C is dissociated from the regulatory domain, probably by a limited proteolysis with calpain, and is markedly activated in vasospasm.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; Animals; Basilar Artery; Calpain; Dipeptides; Dogs; Ischemic Attack, Transient; Isoquinolines; Naphthalenes; Piperazines; Polycyclic Compounds; Protein Kinase C; Vasoconstriction