Developmental changes of Ca2+ handling in mouse ventricular cells from early embryo to adulthood

Transplant of immature cardiomyocytes is recently attracting a great deal of interest as a new experimental strategy for the treatment of failing hearts. Full understanding of normal cardiomyogenesis is essential to make this regenerative therapy feasible. We analyzed the molecular and functional changes of Ca2+ handling proteins during development of the mouse heart from early embryo at 9.5 days postcoitum (dpc) through adulthood. From the early to the late (18 dpc) embryonic stage, mRNAs estimated by the real time PCR for ryanodine receptor (type 2, RyR2), sarcoplasmic reticulum. (SR) Ca2+ pump (type 2, SERCA2) and phospholamban (PLB) increased by 3-15 fold in the values normalized to GAPDH mRNA, although Na+/Ca2+ exchanger (type 1, NCX1) mRNA was unchanged. After birth, there was a further increase in the mRNAs for RyR2, SERCA2 and PLB by 18-33 fold, but a 50% decrease in NCX1 mRNA. The protein levels of RyR2, SERCA2, PLB and NCX1, which were normalized to total protein, showed qualitatively parallel developmental changes. L-type Ca2+ channel currents (ICa-L) were increased during the development (1.3-fold at 18 dpc, 2.2-fold at adult stage, vs. 9.5 dpc). At 9.5 dpc, the Ca2+ transient was, unlike adulthood, unaffected by the SR blockers, ryanodine (5 muM) and thapsigargin (2 muM), and also by a blocker of the Ca2+ entry via Na+/Ca2+ exchanger, KB-R 7943 (1 muM). The Ca2+ transient was abolished after application of nisoldipine (5 muM). These results indicate that activator Ca2+ for contraction in the early embryonic stage depends almost entirely on ICa-L. (C) 2002 Elsevier Science Inc. All rights reserved.