Platelets augment rabbit cerebral artery constriction by activating protein kinase C

Area of Science:

• Cardiovascular Research
• Platelet Physiology
• Cerebrovascular Function

Background:

• Platelets play a role in vascular tone regulation.
• Thrombin is a key mediator in platelet activation and vascular responses.
• Protein kinase C (PKC) is implicated as an intracellular signaling pathway in smooth muscle contraction.

Purpose of the Study:

• To investigate if activated platelets enhance cerebral artery responsiveness to thrombin.
• To determine the role of protein kinase C (PKC) in mediating this effect.
• To explore the influence of the cerebrovascular endothelium on platelet-induced vascular responses.

Main Methods:

• In vitro isometric force measurements on rabbit basilar artery segments.
• Assessment of thrombin concentration-response curves with and without activated human platelets.
• Pharmacological inhibition of protein kinase C (PKC) using staurosporine.
• Experiments with and without the removal of the vascular endothelium.

Main Results:

• Activated platelets significantly increased sensitivity and maximal contraction of basilar arteries to thrombin.
• Inhibition of protein kinase C (PKC) with staurosporine blunted the platelet-induced augmentation.
• Removal of the endothelium potentiated the platelet-induced increase in thrombin responsiveness.

Conclusions:

• Platelet-derived mediators amplify arterial contractile responses to thrombin, potentially via protein kinase C (PKC) activation.
• The cerebrovascular endothelium may exert a protective role by reducing the augmentation of vascular tone induced by activated platelets.
• Increased vascular responsiveness to thrombin by activated platelets may involve PKC-mediated alterations in intracellular calcium sensitivity.