Electrolyte transport in a central core model of the renal medulla.
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.
Stephenson
J L
JL
Department of Physiology, Cornell University Medical College, New York 10021.
Zhang
Y
Y
Eftekhari
A
A
Tewarson
R
R
D001693:Biological Transport, Active; D004573:Electrolytes / Q000378:metabolism*; D007679:Kidney Medulla / Q000378:metabolism*; D007700:Kinetics; D008433:Mathematics; D008954:Models, Biological; D009399:Nephrons / Q000032:analysis; D009994:Osmolar Concentration; D012964:Sodium / Q000378:metabolism
D004573:Electrolytes; D012964:Sodium