['Cardioplegic arrest (CP) and cardiopulmonary bypass (CPB) can lead to dysfunction in the coronary and skeletal microcirculation leading to impaired tissue perfusion. alpha-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.', '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 alpha-adrenergic stimulation with phenylephrine, with and without a PKC-alpha inhibitor or PKC-alpha activator. PKC activity was assessed in isolated microvessels.', 'Western blotting and immunostaining demonstrated only PKC-alpha in coronary and skeletal microvessels. CP/CPB diminished contractile responses to phenylephrine in coronary and skeletal samples. Inhibition of PKC-alpha reduced phenylephrine induced vasoconstriction in coronary and skeletal microvessels, whereas activation of PKC-alpha-augmented phenylephrine induced responses. PKC activity was decreased in coronary microvessels and to an even greater degree in skeletal microvessels after CP/CPB.'] Does protein kinase C alpha modulate microvascular reactivity in the human coronary and skeletal microcirculation?