Hanrahan J W, Phillips J E
Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada.
J Membr Biol. 1984;80(1):15-26. doi: 10.1007/BF01868687.
Models for active Cl transport across epithelia are often assumed to be universal although they are based on detailed studies of a relatively small number of epithelia from vertebrate animals. Epithelial Cl transport is also important in many invertebrates, but little is known regarding its cellular mechanisms.We used short-circuit current, tracer fluxes and ion substitutions to investigate the basic properties of Cl absorption by locust hindgut, an epithelium which is ideally suited for transport studies. Serosal addition of 1 mM adenosine 3':5'-cyclic monophosphate (cAMP), a known stimulant of Cl transport in this tissue, increased short-circuit current (I(sc)) and net reabsorptive (36)C1 flux (J(CI)net) by 1000%. C1 absorption did not exhibit an exchange diffusion component and was highly selective over all anions tested except Br. Several predictions of Na- and HCO3-coupled models for Cl transport were tested: Cl-dependent I(sc) was not affected by sodium removal (<0.05 mM) during the first 75 min. Also, a large stimulation of J(C1)net was elicited by cAMP when recta were bathed for 6 hr in nominally Na-free saline(<0.001 to 0.2 mM) and there was no correlation between C1 transport rate and the presence of micromolar quantities of Na contamination. Increased unidirectional influx of (36)C1 into rectal tissue during cAMP-stimulation was not accompanied by a comparable uptake of (22)Na. J(CI)net was independent of exogenous CO2 and HCO3, but was strongly dependent on the presence of K.These results suggest that the major fraction of C1 transport across this insect epithelium occurs by an unusual K-dependent mechanism that does not directly require Na or HCO3.
尽管跨上皮细胞的主动氯离子转运模型是基于对相对少量脊椎动物上皮细胞的详细研究，但通常被认为具有普遍性。上皮细胞氯离子转运在许多无脊椎动物中也很重要，但其细胞机制却鲜为人知。我们利用短路电流、示踪剂通量和离子替代来研究蝗虫后肠对氯离子吸收的基本特性，蝗虫后肠上皮非常适合进行转运研究。在浆膜侧添加1 mM 3':5'-环磷酸腺苷（cAMP），已知其为该组织中氯离子转运的刺激物，可使短路电流（I(sc)）和净重吸收性(36)C1通量（J(CI)净）增加1000%。C1吸收未表现出交换扩散成分，并且对除Br以外的所有测试阴离子具有高度选择性。我们测试了几种关于Na和HCO3偶联的氯离子转运模型的预测：在前75分钟内，去除钠（<0.05 mM）对氯离子依赖性I(sc)没有影响。此外，当直肠在名义上无钠的盐水（<0.001至0.2 mM）中浸泡6小时时，cAMP可引起J(C1)净的大幅刺激，并且氯离子转运速率与微摩尔量的钠污染的存在之间没有相关性。在cAMP刺激期间，(36)C1向直肠组织的单向流入增加，但并未伴随着(22)Na的相应摄取。J(CI)净独立于外源性CO2和HCO3，但强烈依赖于K的存在。这些结果表明，跨这种昆虫上皮细胞的氯离子转运的主要部分是通过一种不寻常的K依赖性机制发生的，该机制不直接需要Na或HCO3。
