Presence of functional sarcoplasmic reticulum in the developing heart and its confinement to chamber myocardium

Citation
Afm. Moorman et al., Presence of functional sarcoplasmic reticulum in the developing heart and its confinement to chamber myocardium, DEVELOP BIO, 223(2), 2000, pp. 279-290
Citations number
56
Categorie Soggetti
Cell & Developmental Biology
Journal title
DEVELOPMENTAL BIOLOGY
ISSN journal
00121606 → ACNP
Volume
223
Issue
2
Year of publication
2000
Pages
279 - 290
Database
ISI
SICI code
0012-1606(20000715)223:2<279:POFSRI>2.0.ZU;2-F
Abstract
During development fast-contracting atrial and ventricular chambers develop from a peristaltic-contracting heart tube. This study addresses the questi on of whether chamber formation is paralleled by a matching expression of t he sarcoplasmic reticulum (SR) Ca2+ pump. We studied indo-1 Ca2+ transients elicited by held stimulation of linear heart tube stages and of explants f rom atria and outflow tracts of the prototypical preseptational E13 rat hea rt. Ca2+ transients of H/H 11+ chicken hearts, which constitute the prototy pic linear heart tube stage, were sensitive to verapamil only, indicating a minor contribution of Ca2+-triggered SR Ca2+ release. Outflow tract transi ents displayed sensitivity to the inhibitors similar to that of the linear heart tube stages. Atrial Ca2+ transients disappeared upon addition of ryan odine, tetracaine, or verapamil, indicating the presence of Ca2+-triggered SR Ca2+ release. Quantitative radioactive in situ hybridization on sections of E13 rat hearts showed similar to 10-fold higher SERCA2a mRNA levels in the atria compared to nonmyocardial tissue and similar to 5-fold higher exp ression in compact ventricular myocardium. The myocardium of atrioventricul ar canal, outflow tract, inner curvature, and ventricular trabecules displa yed weak expression. Immunohistochemistry on sections of rat and human embr yos showed a similar pattern. The significance of these findings is threefo ld. (i) A functional SR is present long before birth. (ii) SR development i s concomitant with cardiac chamber development, explaining regional differe nces in cardiac function. (iii) The pattern of SERCA2a expression underscor es a manner of chamber development by differentiation at the outer curvatur e, rather than by segmentation of the linear heart tube. (C) 2000 Academic Press.