Mechanism of potentiation by tea epigallocatechin of contraction in porcine coronary artery: The role of protein kinase CI-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 I14M, only EGC, but not other catechins, potentiated high K super(+-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 CI (PKCI) 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 (MLC) sub(2)0). These effects of EGC were inhibited by the PKCI inhibitor rottlerin, but not by the conventional PKC inhibitor Go6976. These results suggest that EGC activates PKCI, leading to the phosphorylation of CPI-17, which in turn inhibits myosin light chain phosphatase and increases MLC sub(20 phosphorylation. The series of events would increase Ca) super(2)+ sensitivity of contractile elements, thereby augmenting high K super(+-induced vascular contraction.)