Julian D, Wieting S L, Seto S L, Bogan M R, Arp A J
Romberg Tiburon Center for Environmental Studies, San Francisco State University, 3152 Paradise Drive, Tiburon, CA 94920, USA.
Physiol Biochem Zool. 1999 Jul-Aug;72(4):416-25. doi: 10.1086/316681.
Oxidation of hydrogen sulfide to thiosulfate is one of the best-characterized mechanisms by which animals adapted to sulfide minimize its toxicity, but the mechanism of thiosulfate elimination in these animals has remained unclear. In this study, we examined the accumulation and elimination of thiosulfate in the sulfide-adapted marine worm Urechis caupo. The coelomic fluid of U. caupo exposed to 50-100 micromol L-1 sulfide in hypoxic seawater (Po2 ca. 10 kPa) accumulated (mean+/-SD) 132+/-41 micromol L-1 thiosulfate after 2 h, reaching 227+/-113 micromol L-1 after an additional 4 h in aerated, sulfide-free seawater. In whole-animal thiosulfate clearance studies, the rate of thiosulfate elimination from the coelomic fluid followed a single exponential time course with a half-life of 6 h. The thiosulfate permeability coefficient of isolated preparations mounted in diffusion chambers was 7.6x10-5+/-7. 7x10-5 cm s-1 for the hindgut and 5.5x10-7+/-2.7x10-7 cm s-1 for the body wall. These rates were independent of the direction of net efflux (mucosal-to-serosal or serosal-to-mucosal). Using a simple mathematical model of U. caupo that incorporates the thiosulfate permeability coefficients, the thiosulfate half-life was calculated to be 23 h without hindgut ventilation but less than 1 h with normal hindgut ventilation. Based on this information, we propose that passive thiosulfate diffusion across the hindgut is adequate to explain the observed rates of thiosulfate elimination.
硫化氢氧化为硫代硫酸盐是动物适应硫化物以将其毒性降至最低的最具特征的机制之一，但这些动物中硫代硫酸盐的消除机制仍不清楚。在本研究中，我们检测了适应硫化物的海洋蠕虫加州星虫体内硫代硫酸盐的积累和消除情况。在低氧海水（氧分压约10 kPa）中暴露于50 - 100 μmol L-1硫化物的加州星虫的体腔液，在2小时后积累了（平均值±标准差）132±41 μmol L-1硫代硫酸盐，在通气的无硫化物海水中再经过4小时后达到227±113 μmol L-1。在全动物硫代硫酸盐清除研究中，体腔液中硫代硫酸盐的消除速率遵循单一指数时间进程，半衰期为6小时。安装在扩散室中的分离制剂的硫代硫酸盐渗透系数，后肠为7.6×10-5±7.7×10-5 cm s-1，体壁为5.5×10-7±2.7×10-7 cm s-1。这些速率与净流出方向（黏膜到浆膜或浆膜到黏膜）无关。使用一个包含硫代硫酸盐渗透系数的简单加州星虫数学模型，计算出在没有后肠通气的情况下硫代硫酸盐半衰期为23小时，但在后肠正常通气的情况下小于1小时。基于这些信息，我们提出硫代硫酸盐在后肠的被动扩散足以解释观察到的硫代硫酸盐消除速率。
