Comparisons of different stages of chick embryonic development by the physiological regulatory response to hyposmotic challenge

Cardiac myocytes isolated and cultured from 11 day chick embryos present a Ca2+-dependent regulatory volume decrease (RVD) when exposed to hyposmotic stimulus. The RVD of myocytes from different embryonic stages were analyzed to evaluate their physiological performance through development. Among the several embryonic stages analyzed (6, 11, 16 and 19 days) only 19 day card iac myocytes present a greater RVD when compared with 11 day (considered as control), the other ages showed no difference in the regulatory response. As it is known that RVD is Ca2+ dependent. we decided to investigate the tr ansient free Ca2+ response during the hyposmotic swelling of the 11 and 19 day stages. The 11 day cardiac myocyte showed a transient 40% increase in i ntracellular free Ca2+ when submitted to hyposmotic solutions, and the free Ca2+ returned to baseline levels while the cells remained in hyposmotic bu ffer. However, the intracellular free Ca2+ transient in the 19 day cells du ring hyposmotic challenge increases 100% and instead of returning to baseli ne levels, declines to 55% above control, well after the 11 day transient h as returned to baseline. Also, quantitative fluorescence microscopy reveale d that 19 day cardiac myocytes have more sarcoplasmic reticulum (SR) Ca2+ A TPase sites per cell as compared to the 11 day cells. Our findings suggest that 19 day cells have more developed intracellular Ca2+ stores (SR). By ev oking the mechanism of Ca2+ induced Ca2+ release, the cells have more free Ca2+ available for signaling the RVD during hyposmotic swelling. (C) 2000 E lsevier Science Inc. All rights reserved.