Beyenbach K W, Freire C A, Kinne R K, Kinne-Saffran E
Section of Physiology, VRT 826, Cornell University, Ithaca, N.Y. 14853.
Miner Electrolyte Metab. 1993;19(4-5):241-9.
That the kidneys of marine fish have powerful renal mechanisms for the excretion of magnesium (Mg) from the body has been known since the early 1930s, but it took another 40 years before the first renal Mg transport model was suggested by Natochin and Gusev. Since rates of net renal sodium (Na) reabsorption were closely correlated with rates of net renal Mg secretion in scorpion fish, Natochin and Gusev proposed tubular Na/Mg exchange transport. However, confirmation of Na/Mg exchange in other fish kidneys has been elusive. Detailed renal clearance studies in sea water rainbow trout have shown that bladder reabsorption of Na and water, the process which concentrates Mg in the bladder, accounts for much of Natochin's original observation. Nevertheless, studies of isolated perfused proximal tubules of the flounder and killifish do show inverse relationships between the concentrations of Na and Mg in the tubule lumen, consistent with Na/Mg exchange. Unfortunately, large paracellular Na permeabilities in renal proximal tubules do not clarify whether paracellular Na fluxes of Na/Mg exchange transport across the brush border membrane are responsible for generating inverse concentrations of Na and Mg in the tubule lumen. These uncertainties have led the authors to their present use of brush border membrane vesicles to look for evidence of Na/Mg exchange transport.
自20世纪30年代初以来，人们就知道海鱼的肾脏具有强大的肾脏机制，可以从体内排泄镁（Mg），但直到40年后，纳托钦和古谢夫才提出了第一个肾脏镁转运模型。由于蝎子鱼的肾脏净钠（Na）重吸收率与肾脏净镁分泌率密切相关，纳托钦和古谢夫提出了肾小管钠/镁交换转运。然而，在其他鱼类肾脏中证实钠/镁交换一直难以实现。对海水虹鳟鱼进行的详细肾脏清除率研究表明，膀胱对钠和水的重吸收，即镁在膀胱中浓缩的过程，是纳托钦最初观察结果的主要原因。尽管如此，对鲽鱼和鳉鱼分离灌注近端小管的研究确实表明，小管腔中钠和镁的浓度呈反比关系，这与钠/镁交换一致。不幸的是，肾脏近端小管中较大的细胞旁钠通透性并不能阐明通过刷状缘膜的钠/镁交换转运的细胞旁钠通量是否是导致小管腔中钠和镁浓度呈反比的原因。这些不确定性导致作者目前使用刷状缘膜囊泡来寻找钠/镁交换转运的证据。
