Changes in Insect Epithelial Metabolism and Active Ion Transport

大多数人都知道鳞翅目（毛毛虫）的幼虫变成蛹（蛹或茧），然后变成成虫（蛾或蝴蝶）所发生的戏剧性变化。这种昆虫的重塑激发了大量关于表皮发育变化的研究。另一方面，昆虫生长发育过程中内部组织的生理代谢变化尚不清楚。这项拟议的研究将揭示在幼虫生长、蜕皮和变态过程中，其中一个组织——中肠的功能变化。所研究的昆虫是烟草角虫（Manduca sexta）。这种毛毛虫本质上是一个“进食机器”，它消耗大量的食物来维持其惊人的生长速度。在幼虫（毛虫）生命的前16天，昆虫的大小增加了近10,000倍。这种快速的生长速度部分是由于其巨大的中肠的功能，消化和吸收摄入的食物。中肠也参与高速率的活性离子运输，这一过程是本研究的重点。在幼虫的生长过程中，m.s sexta在蜕变成蛹之前要蜕皮四次。在每次蜕皮之前，肠道被清除，在蜕皮过程中，新的细胞被添加到中肠。该研究将确定中肠离子运输是否随着幼虫的生长而改变，以及中肠是否在蜕皮过程中暂时停止参与主动离子运输。在第五和最后的幼虫阶段，大的幼虫中肠被破坏并被较小的蛹上皮所取代。PI表明，中肠活性离子转运在这一时期的后半期大大减少。拟议的研究将在Chamberlin的这项工作的基础上进行扩展，通过在蜕皮后到第五阶段以及随后几天的几个时间点测量中肠的活性离子转运。这些研究将精确地确定，在昆虫的变态过程中，活性离子转运何时下降。活性离子运输的能量由有氧代谢提供，因此中肠代谢的变化可能影响活性离子运输。在幼虫生长发育过程中，中肠的代谢组织将通过测量代谢物水平、关键代谢酶的最大活性和分离线粒体的呼吸来确定，线粒体是负责为活性离子运输提供大部分能量的细胞器。这些关于中肠离子转运和代谢的研究将有助于阐明昆虫生长发育过程中内部组织的功能变化。由于蜕皮和变态是所有昆虫共同的过程，因此提出的研究将为了解所有昆虫的生理学提供相关的基础信息。* * *

9407313 Chamberlin Most people are aware of the dramatic transformation that takes place as a larval lepidopteran (caterpillar) changes to a pupa (chrysalis or cocoon) and then to an adult (moth or butterfly). This remodeling of the insect has inspired a great deal of research on the developmental changes in epidermis. On the other hand, changes in the physiology and metabolism of internal tissues during insect growth and development are not well-understood. The proposed research will reveal changes in the functioning of one such tissue, the midgut, during larval growth, molting and metamorphosis. The insect to be studied is the tobacco hornworm (Manduca sexta). This caterpillar is essentially an "eating machine" that consumes large quantities of food to support its phenomenal growth rate. During the first 16 days of larval (caterpillar) life, the insect increases in size nearly 10,000-fold. This rapid growth rate is due, in part, to the functioning of its large midgut which digests and absorbs the ingested food. The midgut also engages in high rates of active ion transport and it is this process that is the focus of the proposed research. During larval growth, M. sexta molts four times before it metamorphoses into a pupa. Prior to each molt the gut is purged and during the molting process new cells are added to the midgut. The proposed research will determine whether midgut ion transport changes as the larva grows and whether the midgut temporarily ceases to engage in active ion transport during the molting process. During the fifth and final larval stage, the large larval midgut is destroyed and replaced by a smaller pupal epithelium. The PI has demonstrated that midgut active ion transport is greatly diminished in the last half of this period. The proposed research will expand upon this work of Chamberlin by measuring active ion transport across midgut just after the molt to the fifth stage and at several time points during the subsequent days . These studies will precisely determine when, in the metamorphosis of the insect, active ion transport declines. The energy for active ion transport is supplied by aerobic metabolism and therefore changes in midgut metabolism may affect active ion transport. The metabolic organization of the midgut during larval growth and development will be determined by measuring metabolite levels, maximal activities of key metabolic enzymes, and the respiration of isolated mitochondria, the organelle responsible for providing most of the energy for active ion transport. These studies on midgut ion transport and metabolism will elucidate the functional changes in an internal tissue during insect growth and development. Since molting and metamorphosis are processes common to all insects, the proposed research will provide fundamental information pertinent to understanding the physiology of all insects. ***