Phillips J E, Wiens C, Audsley N, Jeffs L, Bilgen T, Meredith J
Department of Zoology, University of British Columbia, Vancouver, Canada.
J Exp Zool. 1996 Jul 1;275(4):292-9. doi: 10.1002/(SICI)1097-010X(19960701)275:4<292::AID-JEZ7>3.0.CO;2-K.
Insect epithelia most commonly absorb from KCI-rich, low Na+ fluids. This is true of the locust hindgut, which is functionally analogous to vertebrate kidney tubules. Active absorption of Cl- at the apical membrane is the predominant transport process giving rise to a large short-circuit current (Isc) after stimulation by neuropeptides (CTSH, ITP) via cAMP as second messenger. This Cl- transport is not coupled to or driven secondarily by Na+, K+, HCO3-, Ca2+, or Mg2+ movements. An apical V-type H+ ATPase acidifies the hindgut lumen but at a rate that is 10-15% of Cl-dependent Isc. The evidence to date as to whether the resulting large apical proton gradient is used to drive Cl- transport secondarily by an apical H+/Cl- symport is mixed. Thus a primary mechanism of Cl- absorption remains an alternative possibility. The complete primary structure of a large neuropeptide stimulant (ITP: 72 amino acids) of locust ileal Cl- transport has recently been deduced from its cDNA. This is the first putative insect neuropeptide hormone shown to stimulate ion transport across absorptive epithelia for which the primary sequence has been deduced.
昆虫上皮细胞最常从富含氯化钾、低钠离子的液体中吸收物质。蝗虫后肠就是如此，其功能类似于脊椎动物的肾小管。顶端膜上氯离子的主动吸收是主要的运输过程，在神经肽（CTSH、ITP）通过环磷酸腺苷作为第二信使刺激后会产生很大的短路电流（Isc）。这种氯离子运输与钠离子、钾离子、碳酸氢根离子、钙离子或镁离子的移动没有耦合，也不是由它们继发驱动的。顶端的V型氢离子ATP酶会使后肠管腔酸化，但其速率仅为依赖氯离子的短路电流的10 - 15%。关于由此产生的大的顶端质子梯度是否通过顶端氢离子/氯离子同向转运继发驱动氯离子运输，目前的证据并不一致。因此，氯离子吸收的主要机制仍是一种可能的选择。最近，从其cDNA中推导得出了一种刺激蝗虫回肠氯离子运输的大型神经肽兴奋剂（ITP：72个氨基酸）的完整一级结构。这是首个被证明能刺激离子通过吸收上皮细胞进行运输且已推导得出一级序列的假定昆虫神经肽激素。
