Trimethylamine oxide and the maintenance of volume of dogfish shark rectal gland cells.
Trimethylamine oxide and the maintenance of volume of dogfish shark rectal gland cells.
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三甲胺氧化物与角鲨直肠腺细胞体积的维持。
DOI：
10.1002/jez.1402360103
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发表时间：
1985
期刊：
影响因子：
--
通讯作者：
Kleinzeller,A
中科院分区：
文献类型：
--
作者：
Kleinzeller,A
对角鲨直肠腺细胞稳态体积的决定因素进行了研究。新鲜组织和切片中的三甲胺氧化物(TMAO)在标准(不含TMAO)的弹性支链盐水中有氧孵育60min的细胞水平接近于血浆中的水平(71±5 mM S.E.M.)；因此，在这种条件下，细胞膜似乎对这种溶质是不渗透的。然而，细胞在高K+介质中去极化后，TMAO迅速丧失。因此，TMAO是直肠腺细胞中一种主要的、有效的非天然溶质。细胞溶质在组织水(新鲜切片和孵化切片)中的渗透压与在血浆或孵育液中的渗透压没有显著差异，表明细胞膜上没有渗透压梯度。对稳态条件下一个简单的细胞溶质模型的分析表明，(有效的)非渗透分子的存在降低了细胞内整体阳离子的浓度。这一分析与对细胞Na+和K+在含有高浓度(含氮)渗透分子的组织中的分布的现有观察一致。该模型的一个简化假设，即Na+和K+通过细胞膜的相应反射系数σ相同(或接近)，无法得到验证。与已有的直肠腺切片中42K+稳态细胞通量的数据相比，组织对22Na+的摄取较慢(导出的速率常数k‘=0.017−1，约为K+的十分之一)。因此，σNa<；σK.另一方面，~(36)Cl-−与细胞Cl-−迅速交换，其第一速率常数(k‘=0.60+0.12min−_1)接近于3H2O。
Determinants of the steady‐state vol of the dogfish shark (Squalus acanthias) rectal gland cells were studied. The cellular levels of trimethylamine oxide (TMAO) in fresh tissue and slices incubated aerobically 60 min in standard (TMAO‐free) elasmobranch saline were close to those in the plasma (71 ± 5 mM S.E.M.); therefore, under these conditions, the cell membrane appears to be impermeable to this solute. However, depolarization of the cells in high‐K+media produced a rapid loss of TMAO. Thus, TMAO is a major, effectively impermeant solute in the rectal gland cells. The osmolarity of cell solutes in tissue water (fresh and incubated slices) did not differ significantly from values in the plasma or incubation medium, demonstrating the absence of an osmotic pressure gradient across the cell membrane. An analysis of a simple model of cell solutes under steady‐state conditions shows that the presence of an (effectively) impermeant osmolyte decreases the cellular concentration of bulk cations. The analysis is consistent with available observations on the distribution of cell Na+and K+in tissues containing high concentrations of (nitrogeneous) osmolytes. One simplifying assumption of the model, i.e., identity (or closeness) of the respective reflection coefficients σ for Na+and K+passage through the cell membranes could not be verified. Compared to available data on the steady‐state cellular fluxes of42K+in slices of the rectal gland, the uptake of22Na+by the tissue was slow (the derived rate constant k′ = 0.017 min−1, i.e., about one tenth of that for K+). Hence, σNa< σK. On the other hand,36Cl−rapidly exchanged with cell Cl−with the first rate constant (k′ = 0.60 + 0.12 min−1) close to that of3H2O.
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