Background: Cardioplegic arrest (CP) and cardiopulmonary bypass (CPB) can lead to dysfunction in the coronary and skeletal microcirculation leading to impaired tissue perfusion. α-Adrenergic signaling pathways acting on these microcirculatory beds are thought to involve protein kinase C (PKC). We investigate here the role of the conventional PKCs in microvascular function in the setting of CP/CPB. Methods: Atrial and skeletal muscle was harvested from 30 patients undergoing cardiac surgery before and after CP/CPB. Microvessels were used for Western blotting and immunofluorescent staining against conventional PKCs. Microvascular constriction was assessed in pre- and post-CP/CPB samples in response to α-adrenergic stimulation with phenylephrine, with and without a PKC-α inhibitor or PKC-α activator. PKC activity was assessed in isolated microvessels. Results: Western blotting and immunostaining demonstrated only PKC-α in coronary and skeletal microvessels. CP/CPB diminished contractile responses to phenylephrine in coronary and skeletal samples. Inhibition of PKC-α reduced phenylephrine induced vasoconstriction in coronary and skeletal microvessels, whereas activation of PKC-α-augmented phenylephrine induced responses. PKC activity was decreased in coronary microvessels and to an even greater degree in skeletal microvessels after CP/CPB. Conclusions: PKC-α is the predominant conventional PKC present in the human coronary and skeletal microcirculation. It likely plays a key role in α-adrenergic signaling in microvessels and in the vasomotor dysfunction after CP/CPB.
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