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Theaflavin 3,3′‐digallate (TF3), is reported to protect cardiomyocytes from lipotoxicity and reperfusion injury. However, the role of TF3 in the protection of high‐glucose injury is still poorly understood. This study investigated the protective effects of TF3 on gap junctions and autophagy in neonatal cardiomyocytes (NRCMs). NRCMs preincubated with high glucose were coincubated with TF3. The expression of connexins and autophagy‐related proteins was determined. The functioning of gap‐junctional intercellular communication (GJIC) was measured by a dye transfer assay. Adenosine monophosphate‐activated protein kinase (AMPK) activity was determined by western blot. Moreover, AMPK was activated with aminoimidazole‐4‐carboxamide‐1‐β‐d‐ribofuranoside (AICAR) or inhibited by AMPKα small interfering RNA (siRNA) to explore the role of AMPK in the modulation of connexin 43 (Cx43) and autophagy. Meanwhile, autophagy was activated or blocked to observe the change in Cx43 expression. It was found that the protein expression of Cx43 and autophagy‐related proteins was increased in a TF3 dose‐ and time‐dependent manner under high glucose. TF3 also recovered the reduced GJIC function induced by high glucose concentrations. TF3 activated phosphorylated AMPK in a time‐dependent way. AMPKα siRNA abrogated the protection of TF3, while AICAR showed similar results compared to the TF3 treatment. Meanwhile, autophagy activation caused decreased Cx43, while cotreatment with baf A1 enhanced Cx43 expression further compared with the TF3 treatment alone under high glucose. We concluded that TF3 partly reversed the inhibition of Cx43 expression and autophagy induced by high glucose in NRCMs, partly by restoring AMPK activity. Inhibition of autophagy might be protective by preserving Cx43 expression in NRCMs stimulated by high glucose.

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