Eppley Z A, Russell B
Department of Physiology and Biophysics, University of Illinois, Chicago 60612-7342, USA.
J Morphol. 1995 Sep;225(3):357-67. doi: 10.1002/jmor.1052250307.
Endothermic heat production and the capacity to shiver develop soon after hatching in birds, permitting chicks to regulate their body temperature. Physiological studies have not clearly identified the developmental events causing this change in function. Here, we use electron microscopy to examine the development of structures involved in muscle activation, contraction, and metabolism coincident with the development of shivering thermogenesis. A stereological study was used to compare the ultrastructure of chicken iliofibularis before endothermic heat production was present (24 h before hatching) and 120 h later, when the iliofibularis had substantial capacity for shivering. Profound increases were found in the t-tubule system and terminal cisternae, mitochondrial cristae, and lipids. The number of triadic profiles increased 3.8-fold (7.6 +/- 1.31/100 microns 2 to 28.5 +/- 2.90/100 microns 2 fiber area). The surface area of cristae per mitochondrial volume doubled (12.0 +/- 1.50 microns 2/microns 3 to 25.7 +/- 1.84 microns 2/microns 3). Lipid droplets were rare in the iliofibularis of embryos about to hatch, but accounted for 4.4% of the muscle fiber volume in day 4 birds. We suggest that these ultrastructural changes more fully activate the iliofibularis, allow it to produce more heat both from calcium pumping and from contraction, and increase its endurance, thus permitting the muscle to be effective in thermogenesis.
鸟类孵化后不久就会产生产热和颤抖的能力，这使雏鸡能够调节体温。生理学研究尚未明确确定导致这种功能变化的发育事件。在这里，我们使用电子显微镜来检查与颤抖产热发育同时发生的肌肉激活、收缩和代谢相关结构的发育。我们采用体视学研究方法，比较了在出现产热之前（孵化前24小时）和120小时后鸡髂腓肌的超微结构，此时髂腓肌具有很强的颤抖能力。结果发现，横管系统、终池、线粒体嵴和脂质都有显著增加。三联体轮廓的数量增加了3.8倍（每100微米2纤维面积从7.6±1.31个增加到28.5±2.90个）。每个线粒体体积的嵴表面积增加了一倍（从12.0±1.50微米2/微米3增加到25.7±1.84微米2/微米3）。即将孵化的胚胎的髂腓肌中脂滴很少，但在4日龄雏鸡中占肌肉纤维体积的4.4%。我们认为，这些超微结构的变化更充分地激活了髂腓肌，使其能够通过钙泵和收缩产生更多热量，并提高其耐力，从而使肌肉在产热过程中发挥有效作用。
