Endothelin-1-induced contractile responses of human coronary arterioles via endothelin-A receptors and PKC-α signaling pathways

BackgroundWe investigated the contractile function in responses to endothelin-1 (ET-1) in the human coronary microvasculature as well as the roles of endothelin receptors and protein kinase C-α (PKC-α) in these responses.MethodsHuman atrial tissue was harvested from patients who underwent cardiac surgery pre- and post-cardioplegia (CP)/cardiopulmanory bypass (CPB). Microvascular constriction was assessed in pre- and post-CP/CPB samples in responses to ET-1, in the presence and absence of an endothelin-A (ET-A) receptor antagonist, an endothelin-B (ET-B) receptor antagonist, or a PKC-α inhibitor, respectively. The expression and localization of the ET-A and ET-B receptors were also examined using immunoblot and immunofluorescence photomicroscopy.ResultsThe post-CP/CPB contractile response of coronary arterioles to ET-1 was significantly decreased compared with the pre-CP/CPB responses. The response to ET-1 was significantly inhibited in the presence of the ET-A antagonist BQ123 (10−7mol/L), but these values remained unchanged with the ET-B receptor antagonist BQ788 (10−7mol/L). Pretreatment with the PKC-α inhibitor safingol (2.5 × 10−5 mol/L) reversed the ET-1 responses from contraction into relaxation. The total polypeptide levels of ET-A and ET-B receptors were not altered post-CP/CPB. Immunoblot and immunofluorescent staining displayed strong signals for ET-A receptors and relatively weak signals for ET-B receptors localized on coronary microvasculature.ConclusionCP/CPB decreases the contractile function of human coronary microvessels in responses to ET-1. ET-A receptors are predominantly localized in the human coronary microcirculation, whereas ET-B receptors seem to be less abundant. The contractile response to ET-1 is in part through the activation of ET-A receptors and PKC-α. These results suggest a role of ET-1-induced contraction in the vasomotor dysfunction after cardiac surgery.