1,4,5-Inositol Trisphosphate-Operated Intracellular Ca2+ Stores and Angiotensin-II/Endothelin-1 Signaling Pathway Are Functional in Human Embryonic Stem Cell-Derived Cardiomyocytes

On the basis of previous findings suggesting that in human embryonic stem cell-derived cardiomyocytes (hESC-CM) the sarcoplasmic reticulum Ca2+-induced release of calcium machinery is either absent or immature, in the present study we tested the hypothesis that hESC-CM contain fully functional 1,4,5-inositol trisphosphate (1,4,5-IP3)-operated intracellular Ca2+ ([Ca2+]i) stores that can be mobilized upon appropriate physiological stimuli. To test this hypothesis we investigated the effects of angiotensin-II (AT-II) and endothelin-1 (ET-1), which activate the 1,4,5-IP3 pathway, on [Ca2+]i transients and contractions in beating clusters of hESC-CM. Our major findings were that in paced hESC-CM both AT-II and ET-1 (10−9 to 10−7 M) increased the contraction amplitude and the maximal rates of contraction and relaxation. In addition, AT-II (10−9 to 10−7 M) increased the [Ca2+]i transient amplitude. The involvement of 1,4,5-IP3-dependent intracellular Ca2+ release in the inotropic effect of AT-II was supported by the findings that (a) hESC-CM express AT-II, ET-1, and 1,4,5-IP3 receptors determined by immunofluorescence staining, and (b) the effects of AT-II were blocked by 2 μM 2-aminoethoxyphenyl borate (a 1,4,5-IP3 receptor blocker) and U73122 (a phospholipase C blocker). In conclusion, these findings demonstrate for the first time that hESC-CM exhibit functional AT-II and ET-1 signaling pathways, as well as 1,4,5-IP3-operated releasable Ca2+ stores. Disclosure of potential conflicts of interest is found at the end of this article.