Modulation of cardiac optogenetics by vitamin A

Cardiac optogenetics is an emergent research area and refers to the delivery of light-activated proteins to excitable heart tissue and the subsequent use of light for controlling the electrical function with high spatial and temporal resolution. Channelrhodopsin-2 (ChR2) is a light-sensitive ion channel with the chromophore, all trans retinal, derived from vitamin A (all-trans-retinol; retinol). In this study, we explored whether exogenous vitamin A can be a limiting factor in the light responsiveness of cardiomyocytes-expressing ChR2. We showed that in cardiomyocytes virally transduced with ChR2 (H134R)-enhanced yellow fluorescent protein, vitamin A supplements lower than 10 μM significantly increased ChR2 expression. Adding 1 μM vitamin A changed light-induced transmembrane potential difference significantly, whereas 5 μM dramatically induced membrane depolarization and triggered intracellular calcium elevation. We concluded that vitamin A supplementation can modulate the efficiency of ChR2 and provide a complementary strategy for improving the performance of optogenetic tools.