Epigallocatechin-3 gallate, a green tea catechin, attenuated the downregulation of the cardiac gap junction induced by high glucose in neonatal rat cardiomyocytes.

ABSTRACT

AIMS: The remodeling of cardiac gap junctions has been postulated to contribute to the arrhythmias in a diabetic heart. Epigallocatechin-3 gallate (EGCG), a green tea catechin, has recently been recognized for its protection in cardiovascular disease. This study investigated the effect of EGCG on the possible remodeling of gap junctions under high glucose in cultured neonatal rat cardiomyocytes. METHODS: Cardiomyocytes pre-incubated with high glucose (30mM) were co-treated by EGCG. The expression of Connexin43 (Cx43), Cx40 and Cx45 were determined by Western blot and real-time RT-PCR. The function of cells coupling was evaluated by scrape loading dye transfer study. The Mitogen-activated protein kinases (MAPK) were quantified by Western blot. RESULTS: The protein expression of Cx43 was reduced by high glucose (30mM, 72h). Addition of EGCG to high glucose treated cardiomyocytes attenuated the Cx43 reduction in a dose- and time-dependent manner and also recovered the reduced function of cells coupling. The mRNA or protein level of Cx40 and Cx45 showed no significant change by high glucose (30mM, 72h) or EGCG co-treatment (40microM, 24h). Nor did the Cx43 mRNA level. EGCG (40muM) activated the time-dependent phosphorylated Erk, JNK and p38 MAPK. The p38 MAPK inhibitor SB203580 (10microM), however, attenuated the protective effect of EGCG. CONCLUSION: EGCG could attenuate the downregulation of gap junction induced by high glucose in cultured neonatal rat cardiomyocytes. The p38 MAPK pathway was partly involved in this effect of EGCG.