Scott Graham R, Richards Jeff G, Forbush Biff, Isenring Paul, Schulte Patricia M
Department of Zoology, University of British Columbia, Vancouver, BC, Canada V6T 1Z4.
Am J Physiol Cell Physiol. 2004 Aug;287(2):C300-9. doi: 10.1152/ajpcell.00054.2004. Epub 2004 Mar 24.
Maintenance of ion balance requires that ionoregulatory epithelia modulate ion flux in response to internal or environmental osmotic challenges. We have explored the basis of this functional plasticity in the gills of the euryhaline killifish Fundulus heteroclitus. The expression patterns of several genes encoding ion transport proteins were quantified after transfer from near-isosmotic brackish water [10 parts/thousand (ppt)] to either freshwater (FW) or seawater (SW). Many changes in response to SW transfer were transient. Increased mRNA expression occurred 1 day after transfer for Na(+)-K(+)-ATPase-alpha(1a) (3-fold), Na(+)-K(+)-2Cl(-)-cotransporter 1 (NKCC1) (3-fold), and glucocorticoid receptor (1.3-fold) and was paralleled by elevated Na(+)-K(+)-ATPase activity (2-fold). The transient increase in NKCC1 mRNA expression was followed by a later 2-fold rise in NKCC protein abundance. In contrast to the other genes studied in the present work, mRNA expression of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel generally remained elevated (2-fold) in SW. No change in protein abundance was detected, however, suggesting posttranscriptional regulation. The responses to FW transfer were quite different from those to SW transfer. In particular, FW transfer increased Na(+)-K(+)-ATPase-alpha(1a) mRNA expression and Na(+)-K(+)-ATPase activity to a greater extent than did SW transfer but had no effect on V-type H(+)-ATPase expression, supporting the current suggestion that killifish gills transport Na(+) via Na(+)/H(+) exchange. These findings demonstrate unique patterns of ion transporter expression in killifish gills after salinity transfer and illustrate important mechanisms of functional plasticity in ion-transporting epithelia.
维持离子平衡要求离子调节上皮细胞响应内部或环境渗透压挑战来调节离子通量。我们探究了广盐性鳉鱼（Fundulus heteroclitus）鳃中这种功能可塑性的基础。将鳉鱼从近等渗的微咸水[10‰（ppt）]转移至淡水（FW）或海水（SW）后，对几种编码离子转运蛋白的基因的表达模式进行了定量分析。许多对转移至海水的响应变化是短暂的。转移后1天，钠钾ATP酶-α1a（Na(+)-K(+)-ATPase-alpha(1a)）（3倍）、钠钾2氯协同转运蛋白1（NKCC1）（3倍）和糖皮质激素受体（1.3倍）的mRNA表达增加，同时钠钾ATP酶活性升高（2倍）。NKCC1 mRNA表达的短暂增加之后，NKCC蛋白丰度随后出现2倍的升高。与本研究中其他研究的基因不同，囊性纤维化跨膜电导调节因子（CFTR）氯离子通道的mRNA表达在海水中通常保持升高（2倍）。然而，未检测到蛋白丰度的变化，提示存在转录后调控。对转移至淡水的响应与转移至海水的响应截然不同。特别是，转移至淡水比转移至海水更大程度地增加了钠钾ATP酶-α1a mRNA表达和钠钾ATP酶活性，但对V型氢离子ATP酶表达没有影响，支持了目前关于鳉鱼鳃通过钠氢交换转运钠离子的观点。这些发现证明了盐度转移后鳉鱼鳃中离子转运体表达的独特模式，并阐明了离子转运上皮细胞功能可塑性的重要机制。
