CARDIAC NEURAL CREST IN DEVELOPMENT OF MYOCARDIAL FUNCTI

四种最致命的心脏缺陷中有三种与神经嵴有关，占先天性心脏病治疗总费用的70%。先前的研究发现，心脏兴奋-收缩（EC）耦合受损是神经嵴消融鸡胚胎的主要功能缺陷。在肌细胞和分离的小梁中，由于l型Ca2+电流减少，Ca2+摄取肌浆网（SR）减少，SR Ca2+诱导的Ca2+释放（CICR）减少，细胞内Ca2+瞬态明显减少。此外，每座桥的平均受力也减小了。目的1将验证新的假设，即心脏l型Ca2+电流的降低是由于神经嵴消融后胚胎心脏l型Ca2+通道的功能和/或表达下降。实验旨在确定新合成的Ca2+通道是否插入肌膜；单通道活性是否降低；神经嵴消融胚胎中Ca2+通道亚基的表达是否发生改变。目的2将测试新的假设，即CICR受损与神经嵴消融后细胞外“触发”Ca2+的可用性无关。实验旨在确定CICR是否存在Ca2+敏感性降低；表面膜与SR之间的外周耦合是否成熟；以及CICR增益是否降低。目的3将测试新的假设，即两种机制之一削弱了胚胎心室收缩装置在嵴消融后产生的力。将确定跨桥功能是否正常，但平行弹性（吸收跨桥产生的大部分功）增加；或跨桥功能是否异常。这些研究的结果将提供新的信息，可能导致改善先天性心脏病婴儿的护理和治疗。

Three out of the top four most lethal heart defects are neural crest-related and account for 70% of the total cost of treating congenital heart disease. Prior work identified impaired cardiac excitation-contraction (EC) coupling as the major functional deficit in neural crest-ablated chick embryo. Markedly reduced intracellular Ca2+ transients due to reduced L-type Ca2+ current, decreased Ca2+ uptake into the sarcoplasmic reticulum (SR) and reduced SR Ca2+-induced Ca2+ release (CICR) was documented in myocytes and isolated trabeculae. Furthermore, the average force per crossbridge was decreased. Aim 1 will test the new hypothesis that reduced cardiac L-type Ca2+ current is due to decreased function and/or expression of L-type Ca2+ channels in embryonic heart after neural crest ablation. Experiments are designed to determine if newly synthesized Ca2+ channels are inserted into the sarcolemma; whether single channel activity is reduced; and whether there is altered expression of Ca2+ channel subunits in neural crest-ablated embryos. Aim 2 will test the new hypothesis that CICR is impaired irrespective of the availability of extracellular "trigger" Ca2+ following neural crest ablation. Experiments are designed to determine whether there is decreased Ca2+ sensitivity of CICR; whether peripheral couplings between surface membrane and SR are mature; and whether gain of CICR is reduced. Aim 3 will test the new hypothesis that one of two mechanisms impairs force produce by the contractile apparatus in embryonic ventricle following crest ablation. It will be determined whether cross-bridge function is normal but parallel elasticity (that absorbs much of the work produced by the cross-bridges) is increased; or whether cross-bridge function is abnormal. The results from these studies will provide new information that could lead to improved care and treatment of infants with congenital heart disease.