Sodium‐calcium exchanger (NCX‐1) and calcium modulation: NCX protein expression patterns and regulation of early heart development

Abstract

Ouabain-induced inhibition of early heart development indicated that Na/K-ATPase plays an important role in maintaining normal ionic balances during differentiation of cardiomyocytes (Linask and Gui [1995] In order to identify a connection between heart development and NCX-mediated Ca ؉؉ regulation, we determined the embryonic spatiotemporal protein expression pattern of NCX-1 during early developmental stages. In both chick and mouse embryos, NCX-1 (the cardiac NCX isoform) is asymmetrically expressed during gastrulation; in the right side of the Hensen's node in the chick, in the right lateral mesoderm in the mouse. At slightly later stages, NCX-1 is expressed in the heart fields at comparable stages of heart development, in the chick at stage 7 and in the mouse at embryonic day (ED) 7.5. By ED 8 in the mouse, the exchanger protein displays a rostrocaudal difference in cardiac expression and an outer curvature-inner curvature ventricular difference. By ED 9.5, cardiac expression has increased from that seen at ED8 and NCX-1 is distributed throughout the myocardium consistent with the possibility that it is important in regulating initial cardiac contractile function. Only a low level of expression is detected in inflow and outflow regions. To substantiate a role for the involvement of calcium-mediated signaling, using pharmacologic approaches, ionomycin (a Ca ؉؉ ionophore) was shown to perturb cardiac cell differentiation in a manner similar to ouabain as assayed by cNkx2.5 and sarcomeric myosin heavy chain expression. In addition, we show that an inhibitor of NCX, KB-R7943, can similarly and adversely affect early cardiac development at stage 4/5 and arrests cardiac cell contractility in 12-somite embryos. Thus, based upon NCX-1 protein expression patterns in the embryo, experimental Ca ؉؉ modulation, and inhibition of NCX activity by KB-R7943, these results suggest an early and central role for calcium-mediated signaling in cardiac cell differentiation and NCX's regulation of the initial heartbeats in the embryo.

Partial rescue of the Na+-Ca2+ exchanger (NCX1) knock-out mouse by transgenic expression of NCX1

“…In particular, NCX1 expression is highly restricted to the early embryonic heart and serves an important role in heart development (Koushik et al, 1999;Linask et al, 2001). Moreover, high levels of NCX1 expression and Na + /Ca 2+ exchange activities have also been found in other tissues, such as brain and kidney (reviewed in Friedman, 1998;Sakaue et al, 2000).…”

Calcium Channel Blockade in Embryonic Cardiac Progenitor Cells Disrupts Normal Cardiac Cell Differentiation

“…We previously demonstrated that the Na=K-ATPase, that is, the sodium pump, plays an important role in maintaining normal ionic balances during differentiation of cardiomyocytes [5]. Inhibition of the sodium pump is generally accepted to affect the activity of the Na-Ca exchanger 1; we and others provided evidence that the Na-Ca exchanger 1 drives the initial embryonic heartbeats, as well as disrupts normal myofibrillogenesis [6,7]. A close association appears to exist during cardiomyocyte differentiation among Ca fluxes, differentiation of the contractile apparatus, and maintenance of ionic balances.…”

Expression and reconstitution of the bioluminescent Ca2+ reporter aequorin in human embryonic stem cells, and exploration of the presence of functional IP3 and ryanodine receptors during the early stages of their differentiation into cardiomyocytes

“…In addition, when embryos were treated with a Ca 2+ buffer, BAPTA, one of the most obvious effects was the development of a defective heart; even though a distinct atrium and ventricle were still formed, the heart was smaller than normal and was not capable of pumping blood (Créton et al, 1998). In the chick, when embryos were treated with ouabain or ionomycin to increase the intracellular Ca 2+ either indirectly (via the NCX) or directly, respectively, differentiation of the cells in the posterior areas of the heart-forming region was blocked (Linask et al, 2001). In addition, treatment with KB-R7943, an NCX inhibitor, affected the early development of the heart and blocked the initial heart beats in the chick embryo (Linask et al, 2001).…”

“…In the chick, when embryos were treated with ouabain or ionomycin to increase the intracellular Ca 2+ either indirectly (via the NCX) or directly, respectively, differentiation of the cells in the posterior areas of the heart-forming region was blocked (Linask et al, 2001). In addition, treatment with KB-R7943, an NCX inhibitor, affected the early development of the heart and blocked the initial heart beats in the chick embryo (Linask et al, 2001). Ca 2+ signaling also plays a key role in heart development in mammals.…”