J Exp Biol ：果蝇心跳逆转方向现象的新机制
虽然黑腹果蝇（Drosophila melanogaster）几十年以来早成为了一种模式生物，在许多生物研究中发挥着不可替代的作用，但是近期来自德国埃朗根—纽伦堡弗里德里希—亚力山大大学（University of Erlangen—Nuernberg）的研究人员在果蝇心脏中发现了新的机制，这有助于解释果蝇心跳逆转（heartbeat reversals）方向现象。这一研究成果公布在《实验生物学杂志》（Journal of Experimental Biology）上。
来自加州大学河畔分校的昆虫学家Tom Miller认为，此次发现“从某种意义上来说就像是发现了第三只眼，至少在循环系统研究领域里来说意义重大”，“尤其是在黑腹果蝇中，我们对于这种昆虫了解得比其它动物的多。”
科学家们在许多不同的昆虫中都发现过心跳逆转的现象，这被认为是能改善血淋巴（hemolymph，昆虫的“血”，并不携带氧）循环的一种方式。
埃朗根—纽伦堡大学的Lutz Wasserthal利用穿过身体的红外线光束（infrared beam）观测黑腹果蝇和大型种果蝇（D.hydei）的心脏活动，并记录下来。除了描述了这种逆转，研究人员也利用光学和电子显微镜发现了引起这种行为的解剖构造，他们在心脏中识别出了保证血淋巴循环的ostia -openings的五分之一结构。果蝇中，已知的4对心门（ostia）能在心跳调控过程中，指导从腹部流向心脏的虚幻的血淋巴过程。
来自美国Burnham医学研究所（Burnham Institute for Medical Research）的Rolf Bodmer认为，“这一新发现的解剖学机制加深了我们对于胸腔在血淋巴循环过程中的作用的了解”。
这一发现支持了Wasserthal有关为什么果蝇周期性地逆转血淋巴运动方向的理论——这样能帮助果蝇摄入更多的空气。Wasserthal表示，“所有的人至今都认为果蝇并不能进行空气交换。”大型的昆虫通过气管收缩膨胀交换空气，由于果蝇体形小，其血淋巴并不携带氧气，因此一般假设认为其呼吸系统与其它小型昆虫一样是被动扩散，然而Wasserthal的这一研究证实果蝇也可以通过心跳逆转交换空气。下一步他们将检测心跳过程血淋巴循环。
原始出处:
First published online October 19, 2007
Journal of Experimental Biology 210, 3707-3719 (2007)
Drosophila flies combine periodic heartbeat reversal with a circulation in the anterior body mediated by a newly discovered anterior pair of ostial valves and `venous' channels
Institute of Biology, University of Erlangen-Nuernberg, Staudtstrasse 5, D-91058 Erlangen, Germany
e-mail: ltwthal@biologie.uni-erlangen.de
Accepted 21 August 2007
Heartbeat activity in tethered adult drosophilids was recorded using a linear optosensor chip and an IR-light beam. Recording from two to five sensor elements within 250 µm along the anterior heart, it was possible to analyze periodic reversals. In intact Drosophila melanogaster and D. hydei, longer anterograde pulse periods with lower pulse rates generally alternated with shorter retrograde pulse periods having higher pulse rates. These differences are dependent on heart anatomy: a newly discovered first pair of ostia is connected to bilateral thoraco-abdominal hemolymph channels. These channels are part of a venous space separated from the abdominal hemocoel by a septum, consisting of a metanotal ridge and the pericardial diaphragm lined by a special form of fat body. The channels are sealed, and their lumen is possibly controlled by the metathoracic tergo-pleural muscle. During retrograde pulses, the heart chamber works like a suction pump, aspiring hemolymph through the first ostia from the venous channels and discharging it through a newly described caudal opening. During forward beating, the anterior chamber receives hemolymph via all inflow ostia from the entire heart and drives it like a pressure pump through the narrow aorta. Also, during forward pulses, a lateral circulation occurs in the thorax as a result of the venous supply. Inhibition of abdominal mobility leads to an irregular heart rate, with pulse-wise alternating heartbeat reversals. The possible involvement of slow abdominal movements in heartbeat periodicity is discussed. The heartbeat periods are superimposed with intermittent bouts of abdominal pumping movements.
Key words: anatomy, cardiogenesis, dorsal vessel, Drosophila melanogaster, Drosophila hydei, fruitfly, heart development, inflow tract, insect heart, linear optosensor array, ostium, optocardiography, svp-lacZ
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