Gene expression of Na+/Ca2+ exchanger during development in human heart

Objective: In immature animal hearts, lower activity of sarcoplasmic reticu lum and lower densities of Ca2+ channels highlight the potentially vital ro le of the Na+/Ca2+ exchanger (NCX) to excitation-contraction coupling. To d ate, studies on NCX expression have been restricted to late developmental s tages. The distribution and gene expression of NCX during early ontogeny is not known, especially in humans. In the present report, we systematically characterized changes in NCX gene expression in human heart during developm ent, with particular emphasis in early ontogeny. Methods: Human hearts duri ng early gestation (9- to 20-week gestation), neonatal (1 to 2 days after b irth) and adulthood (18-40 years old) were used. NCX mRNA levels were studi ed using RNase protection Assay (RPA) and NCX protein levels were assessed by Western blot. Wet weight was also used as the tissue base. Immunolocaliz ation studies using confocal microscopy were performed in isolated fetal ca rdiac myocytes. Results: Normalization of NCX mRNA derived from ventricles against an early gestational age (10-week gestation) shows that NCX mRNA le vels nominally increased from 1 to 1.13 at 19-week gestation then decreased to 0.74 (P<0.05) at neonate and further decreased to 0.23 (P<0.05) at adul t stages. NCX protein levels increased from 1 at 9-week gestation to 3 (P<0 .05) at 20-week gestation and then decreased to 1.8 (P<0.05) at neonate and to 1.87 (P<0.05) at adult stages. Confocal imaging of fetal cardiac myocyt es revealed intense homogeneous membrane staining and abundance of NCX prot ein at this stage. Conclusions: The data demonstrate changes in NCX transcr ipt and NCX protein levels as well as total RNA and proteins during human h eart development. Per wet weight, NCX mRNA was 4.5 times greater at early f etal than adult stages and NCX protein was 2 times greater at adult than th e early fetal stage indicating considerable post-transcriptional regulation . These findings provide new insights into the understanding of temporal ch anges in NCX in the developing heart at the gene level. The functional sign ificance remains to be determined. (C) 2000 Elsevier Science B.V. All right s reserved.