Mobasheri A, Mobasheri R, Francis M J, Trujillo E, Alvarez de la Rosa D, Martín-Vasallo P
University Laboratory of Physiology, University of Oxford, London, United Kingdom.
Histol Histopathol. 1998 Jul;13(3):893-910. doi: 10.14670/HH-13.893.
Chondrocytes exist in an unusual and variable ionic and osmotic environment in the extracellular matrix of cartilage and are responsible for maintaining the delicate equilibrium between extracellular matrix synthesis and degradation. The mechanical performance of cartilage relies on the biochemical properties of the matrix. Alterations to the ionic and osmotic extracellular environment of chondrocytes have been shown to influence the volume, intracellular pH and ionic content of the cells, which in turn modify the synthesis and degradation of extracellular matrix macromolecules. Physiological ion homeostasis is fundamental to the routine functioning of cartilage and the factors that control the integrity of this highly evolved and specialized tissue. Ion transport in cartilage is relatively unexplored and the biochemical properties and molecular identity of membrane transport mechanisms employed by chondrocytes in the control of intracellular ion concentrations and pH is not fully defined and this review focuses on these processes. Chondrocytes have been shown to express voltage and stretch activated ion channels, passive exchangers and ATP dependent ion pumps. In addition, recent studies of transport systems in chondrocytes have demonstrated the presence of isozyme diversity that includes Na+/H+ exchange (NHE1, NHE3), Na+, K(+)-ATPase (several isoforms) and others each of which possess considerably different kinetic properties and modes of regulation. This multitude of isozyme diversity indicates the highly specialized handling of ions and protons in order to accomplish a fine regulation of their transmembrane fluxes. The complexities of these transport systems and their patterns of isoform expression underscore the subtlety of ion homeostasis and pH regulation in normal cartilage. Perturbations in these mechanisms may affect the physiological turnover of cartilage and thus increase the susceptibility to degenerative joint disease.
软骨细胞存在于软骨细胞外基质中异常且多变的离子和渗透环境中，负责维持细胞外基质合成与降解之间的微妙平衡。软骨的力学性能依赖于基质的生化特性。已表明软骨细胞离子和渗透细胞外环境的改变会影响细胞的体积、细胞内pH值和离子含量，进而改变细胞外基质大分子的合成与降解。生理离子稳态是软骨正常功能以及控制这种高度进化和特殊组织完整性的因素的基础。软骨中的离子转运相对未被充分探索，软骨细胞用于控制细胞内离子浓度和pH值的膜转运机制的生化特性和分子特性尚未完全明确，本综述聚焦于这些过程。已表明软骨细胞可表达电压和牵张激活离子通道、被动交换体和ATP依赖性离子泵。此外，最近对软骨细胞转运系统的研究表明存在同工酶多样性，包括钠/氢交换体（NHE1、NHE3）、钠钾ATP酶（几种同工型）等，每种同工酶都具有相当不同的动力学特性和调节模式。这种众多的同工酶多样性表明对离子和质子进行高度专业化处理，以实现对其跨膜通量的精细调节。这些转运系统的复杂性及其同工型表达模式强调了正常软骨中离子稳态和pH调节的微妙性。这些机制的紊乱可能会影响软骨的生理更新，从而增加患退行性关节疾病的易感性。
