TRPC3 regulates the automaticity of embryonic stem cell-derived cardiomyocytes

Abstract Background Cardiac pacemaking is a complex phenomenon that is not completely understood. Canonical transient receptor potential isoform 3 (TRPC3) channel is a cation channel that permeates both Ca 2+ and Na + . TRPC3 was previously found to express in adult cardiomyocytes. However, its role in cardiac pacemaking is unexplored. Here we used mouse embryonic stem cell-derived cardiomyocytes (mESC-CMs) to investigate whether TRPC3 regulates the spontaneous automaticity and the underlying mechanism involved. Methods and results Immunocytochemistry results showed that TRPC3 is expressed at the T-tubules of mESC-CMs. Whole-cell patch clamping showed that single mESC-CMs contain TRPC3 current. Confocal Ca 2+ imaging showed that the TRPC3-specific blocker Pyr3 decreased Ca 2+ transients and local Ca 2+ release (LCR) of mESC-CMs. Combined current and voltage clamp recordings from the same cell showed that reducing the TRPC3 current, either by Pyr3 or a dominant negative (loss-of-function) construct of TRPC3, decreased the pacemaker activity of mESC-CMs as reflected by a decrease in action potential rate, a depolarized maximum diastolic potential and a decrease in slope of phase 4 diastolic depolarization. Furthermore, decreasing the TRPC3 current diminished, while increasing the TRPC3 current augmented the sodium–calcium exchanger (NCX) current in mESC-CMs. Lastly, decrease in TRPC3 current decreased the phosphorylation of ryanodine receptor isoform 2 at Ser2809 and phospholamban at Thr17. Conclusions TRPC3 positively regulates diastolic depolarization of spontaneous action potential by increasing LCR and NCX current and therefore is an important determinant in pacemaking of mESC-CMs.