虹鳟（Oncorhynchus mykiss）鳃基底外侧膜存在尿素易化扩散的证据。
Evidence for facilitated diffusion of urea across the gill basolateral membrane of the rainbow trout (Oncorhynchus mykiss).
作者信息
McDonald M Danielle, Wood Chris M
机构信息
Department of Biology, McMaster University, Hamilton, Ontario, Canada, L8S 4K1.
出版信息
Biochim Biophys Acta. 2004 May 27;1663(1-2):89-96. doi: 10.1016/j.bbamem.2004.02.009.
Recent in vivo evidence suggests that the mechanism of branchial urea excretion in the ammoniotelic rainbow trout (Oncorhynchus mykiss) is carrier-mediated. Further characterization of this proposed mechanism was achieved by using an in vitro isolated basolateral membrane vesicle (BLMV) preparation in which isolated gill membranes were used to determine a variety of physiological properties of the transporter. BLMV demonstrated two components of urea uptake, a linear component at concentrations up to 17.5 mmol x l(-1) and a saturable component (K(0.5)=0.35+/-0.01 mmol x l(-1); V(max)=0.14+/-0.02 micromol mg protein(-1) h(-1)) with a Hill constant of 1.35+/-0.18 at low, physiologically relevant urea concentrations (<2 mmol x l(-1)). Saturable uptake of urea at 1 mmol x l(-1) by BLMV was reduced by 88.5% when incubated with 0.25 mmol x l(-1) phloretin, a potent blocker of UT-type facilitated diffusion urea transport mechanisms. BLMV also demonstrated differential handling of urea versus urea analogues at 1 mmol x l(-1) concentrations and total analogue/total urea uptake ratios were 32% for acetamide and 84% for thiourea. Saturable urea uptake at 1 mmol x l(-1) was significantly reduced by almost 100% in the presence of 5 mmol x l(-1) thiourea but was not affected by 5 mmol x l(-1) acetamide or 5 mmol x l(-1) N-methylurea. Lastly, total urea uptake at 1 mmol x l(-1) by BLMV was sensitive to temperatures above and below the temperature of acclimation with a Q(10)>2 suggesting a protein carrier-mediated process. Combined, this evidence indicates that a facilitated diffusion urea transport mechanism is likely present in the basolateral membrane of the rainbow trout gill.
最近的体内证据表明，氨排泄型虹鳟（Oncorhynchus mykiss）鳃尿素排泄的机制是载体介导的。通过使用体外分离的基底外侧膜囊泡（BLMV）制剂，对这一提出的机制进行了进一步表征，其中分离的鳃膜用于确定转运体的各种生理特性。BLMV显示出尿素摄取的两个成分，浓度高达17.5 mmol·L⁻¹时为线性成分，在低的、生理相关的尿素浓度（<2 mmol·L⁻¹）下为可饱和成分（K(0.5)=0.35±0.01 mmol·L⁻¹；V(max)=0.14±0.02 μmol mg蛋白质⁻¹ h⁻¹），希尔常数为1.35±0.18。当与0.25 mmol·L⁻¹的根皮素（一种UT型易化扩散尿素转运机制的有效阻滞剂）一起孵育时，BLMV在1 mmol·L⁻¹时对尿素的可饱和摄取降低了88.5%。BLMV在1 mmol·L⁻¹浓度下也显示出对尿素与尿素类似物的不同处理，乙酰胺的总类似物/总尿素摄取率为32%，硫脲为84%。在5 mmol·L⁻¹硫脲存在下，1 mmol·L⁻¹时的可饱和尿素摄取显著降低了近100%，但不受5 mmol·L⁻¹乙酰胺或5 mmol·L⁻¹ N-甲基脲的影响。最后，BLMV在1 mmol·L⁻¹时的总尿素摄取对高于和低于驯化温度的温度敏感，Q(10)>2，表明是蛋白质载体介导的过程。综合起来，这些证据表明虹鳟鳃的基底外侧膜中可能存在易化扩散尿素转运机制。
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