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首页> 外文期刊>Cellular Physiology and Biochemistry >Characterisation of inorganic phosphate transport in bovine articular chondrocytes
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Characterisation of inorganic phosphate transport in bovine articular chondrocytes

机译：牛关节软骨细胞中无机磷酸盐转运的表征

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摘要

In mineralising tissues such as growth plate cartilage extracellular organelles derived from the chondrocyte membrane are present. These matrix vesicles (MV) possess membrane transporters that accumulate Ca2+ and inorganic phosphate (P-i), and initiate the formation of hydroxyapatite crystals. MV are also present in articular cartilage, and hydroxyapatite crystals are believed to promote cartilage degradation in osteoarthritic joints. In the present study, P-i transport pathways in isolated bovine articular chondrocytes have been characterised. P-i uptake was temperature-sensitive and could be resolved into Na+-dependent and Na+-independent components. The Na+-dependent component saturated at high concentrations of extracellular P-i, with a K-m for P-i of 0.17mM. In solutions lacking Na+, uptake did not fully saturate, implying that under these conditions carrier-mediated uptake is supplemented by a diffusive pathway. Both Na+-dependent and Na+-independent components were sensitive to the P-i transport inhibitors phosphonoacetate and arsenate, although a fraction of Na+-independent P-i uptake was resistant to these anions. Total P-i uptake was optimal at pH 7.4, and reduced as pH was made more acidic or more alkaline, an effect that represented reduced Na+-dependent influx. RT-PCR analysis confirmed that two members of the NaPi III family, Pit-1 and Pit-2, are expressed, but that NaPi II transporters are not.
机译：在诸如生长板软骨的矿化组织中，存在源自软骨细胞膜的细胞外细胞器。这些基质囊泡（MV）具有积累Ca2 +和无机磷酸盐（P-i）并启动羟基磷灰石晶体形成的膜转运蛋白。 MV也存在于关节软骨中，并且羟基磷灰石晶体被认为促进骨关节炎关节中的软骨降解。在本研究中，已表征了分离的牛关节软骨细胞中的P-i转运途径。 P-1摄取对温度敏感，可以分解为Na +依赖性和Na +依赖性成分。 Na +依赖性成分在高浓度的细胞外P-i时饱和，P-i的K-m为0.17mM。在缺少Na +的溶液中，吸收并未完全饱和，这意味着在这些条件下，载体介导的吸收可以通过扩散途径得到补充。尽管部分不依赖于Na +的P-i吸收对这些阴离子有抵抗力，但依赖Na +的成分和不依赖于Na +的成分都对P-i转运抑制剂膦酰乙酸和砷酸根敏感。在pH 7.4时，P-i的总摄入量最佳，并且随着pH变得更酸性或更碱性而降低，这一作用表明Na +依赖性流入减少。 RT-PCR分析证实表达了NaPi III家族的两个成员Pit-1和Pit-2，但没有表达NaPi II转运蛋白。

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