Protein kinase Cδ and pharmacomechanical coupling: Re-envisioning cerebral vascular control

Constrictor stimuli set arterial tone through coupling processes dependent (electromechanical) and independent (pharmacomechanical) of V_M. As the latter receives limited attention, we conducted a focused examination of the cerebral circulation to identify key signalling kinases involved in tone development and their role in regulating blood flow. A multiscale approach was implemented extending from cells to live brain and including myography, western blotting, immunolabelling, two-photon microscopy and modelling. We began by superfusing a G protein-coupled receptor agonist (U46619) onto isolated mouse cerebral arteries to drive a concentration-dependent constriction. Using pharmacology to separate the two processes, electromechanical coupling notably preceded pharmacomechanical, the latter tied to protein kinase C (PKC) activation. PKCδ mediated the pharmacomechanical response, irrespective of whether the agonist was superfused or discretely applied to elicit focal non-electrical constriction. Further analysis revealed (1) the translocation of PKCδ to the membrane, indicating its activation, and (2) the identification of C-kinase-activated protein phosphatase-1 inhibitor of 17 kDa (CPI-17) and heat shock protein 27 (HSP27) as downstream phosphorylation targets of PKCδ involved in regulating tone. Focal non-electrical constriction was observed in vivo along penetrating arterioles, responses dependent on PKCδ. Key findings were confirmed in human cerebral arteries, and modelling demonstrated how focal, non-electrical control sets cerebral blood flow distribution. We conclude pharmacomechanical coupling is robust in cerebral arteries and enabled by PKCδ through phosphorylation of CPI-17 and HSP27. This process allows arteries to focally constrict and presumptively optimize blood flow distribution when discrete stimuli are produced. We discuss how aberrant pharmacomechanical control could underlie focal vascular pathobiology and if PKCδ could be a target for therapeutic control. KEY POINTS: Constrictors set arterial tone through coupling processes dependent (electromechanical) and independent (pharmacomechanical) of membrane potential. The relative contribution of electro- and pharmacomechanical coupling to cerebral arterial tone depends to the concentration and area to which constrictors are applied. Protein kinase Cδ is a key transduction protein within pharmacomechanical coupling that enables a focal segment of cerebral artery to constrict independently of the lengthier vessel. Focal constriction is observed in live cerebral microcirculation and it helps set proper blood flow distribution within the brain.