Mechanism of potentiation by tea epigallocatechin of contraction in porcine coronary artery: The role of protein kinase Cδ-mediated CPI-17 phosphorylation

The effects of green tea catechins, (+)- and (−)-catechins (C), (−)-epicatechin (EC), (−)-epicatechin gallate (ECG), (−)-epigallocatechin (EGC), and (−)-epigallocatechin gallate (EGCG), on vascular contractility were investigated in porcine coronary artery. At the concentration of 200 μM, only EGC, but not other catechins, potentiated high K+-induced contraction in a concentration-dependent manner, although EGC by itself did not produce contraction. The potentiator effect of EGC was still observed in endothelium-denuded preparations. Moreover, EGC increased the translocation of protein kinase Cδ (PKCδ) from the cytosol to the plasma membrane and increased phosphorylations of 17-kDa PKC-potentiated protein phosphatase inhibitor protein (CPI-17) and myosin light chain (MLC20). These effects of EGC were inhibited by the PKCδ inhibitor rottlerin, but not by the conventional PKC inhibitor Gö6976. These results suggest that EGC activates PKCδ, leading to the phosphorylation of CPI-17, which in turn inhibits myosin light chain phosphatase and increases MLC20 phosphorylation. The series of events would increase Ca2+ sensitivity of contractile elements, thereby augmenting high K+-induced vascular contraction.