Marsigliante S, Muscella A, Barker S, Storelli C
Dipartimento di Biologia, Laboratorio di Fisiologia, Università di Lecce, Via Provinciale per Monteroni, 73100, Lecce, Italy.
J Endocrinol. 2000 Apr;165(1):147-56. doi: 10.1677/joe.0.1650147.
We have previously shown that angiotensin II (Ang II) has a role at the level of the eel gill chloride cell regulating sodium balance, and therefore osmoregulation; the purpose of the present study was to extend these findings to another important osmoregulatory organ, the kidney. By catalytic histochemistry Na(+)/K(+)ATPase activity was found in both sea water (SW)- and freshwater (FW)-adapted eel kidney, particularly at the level of both proximal and distal tubules. Quantitation of tubular cell Na(+)/K(+)ATPase activity, by imaging, gave values in SW-adapted eels which were double those found in FW-adapted eels (Student's t-test: P<0.0001). This was due to a reduced number of positive tubules present in FW-adapted eels compared with SW-adapted eels. By conventional enzymatic assay, the Na(+)/K(+)ATPase activity in isolated tubular cells from SW-adapted eels showed values 1.85-fold higher those found in FW-adapted eels (Student's ttest: P<0.0001). Perfusion of kidney for 20 min with 100 nM Ang II provoked a significant increase (1.8-fold) in Na(+)/K(+)ATPase activity in FW, due to up-regulation of Na(+)/K(+)ATPase activity in a significantly larger number of tubules (Student's t-test: P<0.0001). The effect of 100 nM Ang II in SW-adapted kidneys was not significant. Stimulation with increasing Ang II concentrations was performed on isolated kidney tubule cells: Ang II provoked a dose-dependent stimulation of the Na(+)/K(+)ATPase activity in FW-adapted eels, reaching a maximum at 100 nM (1.82-fold stimulation), but no significant effect was found in SW-adapted eels (ANOVA: P<0.001 and P>0.05 respectively). Isolated tubule cells stimulated with 100 nM Ang II showed a significant generation of inositol trisphosphate (InsP(3)) and an increment in calcium release from intracellular stores. In conclusion, our results suggest that tubular Na(+)/K(+)ATPase is modulated by environmental salinity, and that Ang II has a role in regulating its activity in FW-adapted eels, probably through an InsP(3)-dependent mechanism.
我们之前已经表明，血管紧张素II（Ang II）在调节钠平衡进而调节渗透平衡的鳗鱼鳃氯细胞水平发挥作用；本研究的目的是将这些发现扩展到另一个重要的渗透调节器官——肾脏。通过催化组织化学法发现，在适应海水（SW）和淡水（FW）的鳗鱼肾脏中均存在Na(+)/K(+)ATP酶活性，特别是在近端和远端小管水平。通过成像对肾小管细胞Na(+)/K(+)ATP酶活性进行定量分析，结果显示适应SW的鳗鱼的值是适应FW的鳗鱼的两倍（学生t检验：P<0.0001）。这是因为与适应SW的鳗鱼相比，适应FW的鳗鱼中阳性小管数量减少。通过传统酶法测定，来自适应SW的鳗鱼的分离肾小管细胞中的Na(+)/K(+)ATP酶活性值比适应FW的鳗鱼高1.85倍（学生t检验：P<0.0001）。用100 nM Ang II灌注肾脏20分钟，可使FW中的Na(+)/K(+)ATP酶活性显著增加（1.8倍），这是由于大量小管中的Na(+)/K(+)ATP酶活性上调所致（学生t检验：P<0.0001）。100 nM Ang II对适应SW的肾脏的作用不显著。对分离的肾小管细胞用递增浓度的Ang II进行刺激：Ang II可引起适应FW的鳗鱼的Na(+)/K(+)ATP酶活性呈剂量依赖性刺激，在100 nM时达到最大值（刺激1.82倍），但在适应SW的鳗鱼中未发现显著影响（方差分析：分别为P<0.001和P>0.05）。用100 nM Ang II刺激的分离肾小管细胞显示出显著生成肌醇三磷酸（InsP(3)）以及细胞内储存的钙释放增加。总之，我们的结果表明肾小管Na(+)/K(+)ATP酶受环境盐度调节，并且Ang II在调节适应FW的鳗鱼中其活性方面发挥作用，可能是通过依赖InsP(3)的机制。
