Stephenson J L, Zhang Y, Eftekhari A, Tewarson R
Department of Physiology, Cornell University Medical College, New York 10021.
Am J Physiol. 1987 Nov;253(5 Pt 2):F982-97. doi: 10.1152/ajprenal.1987.253.5.F982.
Transport of Na+, K+, Cl-, urea, and water is described in a central core model of the renal medulla. Equations for mass balance, Poiseuille flow, and the Nernst-Planck equation describe the continuous behavior of the system along the medullary axis and along the distal nephron; the Kedem and Katchalsky phenomenology describes passive transmural transport; active transmural transport obeys Michaelis-Menten kinetics. Numerical solution of the differential equations shows that to a close approximation any combination of active Na+ and active Cl- transport can generate the same concentration profiles but will generate very different potential profiles, and consequently, very different K+ absorption in thick ascending limb of Henle's loop. If a net transport stoichiometry of 2 Cl- ions to 1 Na+ ion is selected for the pumps, an active Cl- transport rate of approximately 10,000 peq.s-1.cm-2 gives K+ and Na+ concentrations in early distal nephron and a medullary osmolality profile in reasonable agreement with experimental data.
肾髓质的中心核模型描述了Na⁺、K⁺、Cl⁻、尿素和水的转运。质量平衡方程、泊肃叶流动方程和能斯特 - 普朗克方程描述了该系统沿髓质轴和远曲小管的连续行为；凯德姆和卡查尔斯基现象学描述了被动跨膜转运；主动跨膜转运遵循米氏动力学。微分方程的数值解表明，在近似情况下，任何主动Na⁺和主动Cl⁻转运的组合都可以产生相同的浓度分布，但会产生非常不同的电位分布，因此，在亨氏袢厚升支中会产生非常不同的K⁺吸收。如果为泵选择2个Cl⁻离子对1个Na⁺离子的净转运化学计量比，大约10,000 peq·s⁻¹·cm⁻²的主动Cl⁻转运速率会使远曲小管早期的K⁺和Na⁺浓度以及髓质渗透压分布与实验数据合理相符。
