TRPC3 regulates the automaticity of embryonic stem cell-derived cardiomyocytes

BackgroundCardiac 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 Ca2 + 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 resultsImmunocytochemistry 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 Ca2 + imaging showed that the TRPC3-specific blocker Pyr3 decreased Ca2 + transients and local Ca2 + 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.ConclusionsTRPC3 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.