The Multi-Ion Toxicity (MIT) Model uses electrochemical theory to predict the transepithelial potential (TEP) across the gills as an index of major ion toxicity in freshwater animals. The goal is to determine environmental criteria that will be protective of aquatic organisms exposed to salt pollution. In recent studies, TEP disturbances above baseline (ΔTEP) during short-term exposures to major ions have been proven as indicative of their toxicity to fish, in accord with the MIT model. However, the acute 1-h exposures used in these previous studies might not be realistic relative to the 24 h or 96 h test periods used for toxicity assessment. To address this temporal inconsistency, the current study investigated both the TEP responses to serial concentrations of 10 major salts (NaCl, Na₂SO₄, NaHCO₃, KCl, K₂SO₄, KHCO₃, CaCl₂, CaSO₄, MgCl₂, MgSO₄) and plasma ion levels in juvenile rainbow trout after they had been pre-exposed to 50% of the 96h-LC50 levels of these same salts for 4 days. The pre-exposures caused no mortalities. In general, plasma ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻) were well-regulated; however, pre-exposure to sulfate salts resulted in the greatest number of alterations in plasma ion levels. TEP responses remained largely similar to those of naïve trout (without salt pre-exposure). All salts caused hyperbolic concentration-dependent increases in TEP that were well-described by the Michaelis-Menten equation. In the pre-exposed trout, the variation of ∆TEP at the 96h-LC50 concentrations was only 2.2-fold, compared to nearly 28-fold variation among the molar concentrations of the various salts at the 96h-LC50s, identical to the conclusion for naïve trout. Overall, the results remove the temporal inconsistency of previous tests and remain supportive of the MIT model. In addition, the recorded alterations in certain plasma ions, baseline TEP, and Michaelis-Menten constants improve our knowledge on specific physiological responses after extended major ion exposure.

多离子毒性 (MIT) 模型使用电化学理论预测跨鳃的跨上皮电位 (TEP) 作为淡水动物主要离子毒性的指标。目标是确定保护暴露于盐污染的水生生物的环境标准。在最近的研究中，与 MIT 模型一致，在短期暴露于主要离子期间高于基线的 TEP 扰动 (ΔTEP) 已被证明表明它们对鱼类具有毒性。然而，与用于毒性评估的 24 小时或 96 小时测试期相比，这些先前研究中使用的急性 1 小时暴露可能不现实。为了解决这种时间上的不一致性，目前的研究调查了 TEP 对 10 种主​​要盐的系列浓度（NaCl、Na ₂ SO ₄, NaHCO ₃ , KCl, K ₂ SO ₄ , KHCO ₃ , CaCl ₂ , CaSO ₄ , MgCl ₂ , MgSO ₄ ) 和幼年虹鳟鱼在预暴露于 96h-LC50 水平的 50% 后的血浆离子水平这些相同的盐4天。预暴露没有造成死亡。一般来说，等离子体离子（Na ⁺、K ⁺、Ca ²⁺、Mg ²⁺、Cl ^-)受到良好监管；然而，预先暴露于硫酸盐会导致血浆离子水平发生最大数量的变化。TEP 反应与幼鳟鱼的反应基本相似（没有盐预暴露）。所有盐都会导致 TEP 的双曲线浓度依赖性增加，这在 Michaelis-Menten 方程中得到了很好的描述。在预先暴露的鳟鱼中，ΔTEP 在 96h-LC50 浓度下的变化仅为 2.2 倍，而在 96h-LC50 时各种盐的摩尔浓度变化近 28 倍，与天真的鳟鱼。总体而言，结果消除了先前测试的时间不一致并仍然支持 MIT 模型。此外，记录的某些等离子离子、基线 TEP、