Hwang Pung-Pung
Institute of Cellular and Organismic Biology, Academia Sinica, Nankang, Taipei, Taiwan, Republic of China.
J Exp Biol. 2009 Jun;212(Pt 11):1745-52. doi: 10.1242/jeb.026054.
Transepithelial transport is one of the major processes involved in the mechanism of homeostasis of body fluids in vertebrates including fish. The current models of ion regulation in fish gill ionocytes have been proposed mainly based on studies in traditional model species like salmon, trout, tilapia, eel and killifish, but the mechanisms are still being debated due to the lack of convincing molecular physiological evidence. Taking advantage of plentiful genetic databases for zebrafish, we studied the molecular/cellular mechanisms of ion regulation in fish skin/gills. In our recently proposed model, there are at least three subtypes of ionocytes in zebrafish skin/gills: Na(+)-K(+)-ATPase-rich (NaR), Na(+)-Cl(-) cotransporter (NCC) and H(+)-ATPase-rich (HR) cells. Specific isoforms of transporters and enzymes have been identified as being expressed by these ionocytes: zECaC, zPMCA2 and zNCX1b by NaR cells; zNCC gill form by NCC cells; and zH(+)-ATPase, zNHE3b, zCA2-like a and zCA15a by HR cells. Serial molecular physiological experiments demonstrated the distinct roles of these ionocytes in the transport of various ions: HR, NaR and NCC cells are respectively responsible for acid secretion/Na(+) uptake, Ca(2+) uptake and Cl(-) uptake. The expression, regulation and function of transporters in HR and NaR cells are much better understood than those in NCC cells. The basolateral transport pathways in HR and NCC cells are still unclear, and the driving forces for the operations of apical NHE and NCC are another unresolved issue. Studies on zebrafish skin/gill ionocytes are providing new insights into fish ion-regulatory mechanisms, but the zebrafish model cannot simply be applied to other species because of species differences and a lack of sufficient molecular physiological evidence in other species.
跨上皮运输是包括鱼类在内的脊椎动物体液稳态机制中的主要过程之一。目前鱼类鳃离子细胞中离子调节的模型主要是基于对鲑鱼、鳟鱼、罗非鱼、鳗鱼和鳉鱼等传统模式物种的研究提出的，但由于缺乏令人信服的分子生理学证据，其机制仍存在争议。利用丰富的斑马鱼遗传数据库，我们研究了鱼类皮肤/鳃中离子调节的分子/细胞机制。在我们最近提出的模型中，斑马鱼皮肤/鳃中至少有三种离子细胞亚型：富含钠钾ATP酶（NaR）的细胞、钠氯共转运体（NCC）细胞和富含氢离子ATP酶（HR）的细胞。已经确定这些离子细胞表达特定的转运蛋白和酶异构体：NaR细胞表达zECaC、zPMCA2和zNCX1b；NCC细胞表达鳃型zNCC；HR细胞表达zH(+) - ATP酶、zNHE3b、zCA2 - like a和zCA15a。一系列分子生理学实验证明了这些离子细胞在各种离子运输中的不同作用：HR细胞、NaR细胞和NCC细胞分别负责酸分泌/钠离子摄取、钙离子摄取和氯离子摄取。与NCC细胞相比，人们对HR细胞和NaR细胞中转运蛋白的表达、调节和功能了解得更多。HR细胞和NCC细胞的基底外侧运输途径仍不清楚，顶端NHE和NCC运作的驱动力是另一个未解决的问题。对斑马鱼皮肤/鳃离子细胞的研究为鱼类离子调节机制提供了新的见解，但由于物种差异以及其他物种缺乏足够的分子生理学证据，斑马鱼模型不能简单地应用于其他物种。
