Simulation of the Profile of Water, NaCl, and Urea Transport in the Countercurrent Multiplication System between Thin Ascending Limb and Inner Medullary Collecting Duct.

Hamada, Yoshiaki; Imai, Masashi; Aoki, Takao; Suzuki, Ryoji; Kamiya, Akira

doi:10.1620/tjem.168.47

Cited by 4 publications

(8 citation statements)

References 40 publications

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“…A different model for generation of a single effect (luminal osmolality Ͼ interstitial osmolality) in the IMCD, based on a difference in reflection coefficients for urea and NaCl, has been proposed several times (2,5,6,20,27,65,68). The principle is similar to that proposed for generation of a single effect in the thin descending limb as discussed above, except that the directions of the transepithelial urea and NaCl gradients in the IMCD are opposite those seen in the descending limb.…”

Section: Single Effect In the Collecting Ductmentioning

confidence: 99%

Concentration of solutes in the renal inner medulla: interstitial hyaluronan as a mechano-osmotic transducer

Knepper

Saidel

Hascall

et al. 2003

American Journal of Physiology-Renal Physiology

112

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. Concentration of solutes in the renal inner medulla: interstitial hyaluronan as a mechano-osmotic transducer. Am J Physiol Renal Physiol 284: F433-F446, 2003; 10.1152/ajprenal.00067.2002Although the concentrating process in the renal outer medulla is well understood, the concentrating mechanism in the renal inner medulla remains an enigma. The purposes of this review are fourfold. 1) We summarize a theoretical basis for classifying all possible steady-state inner medullary countercurrent concentrating mechanisms based on mass balance principles. 2) We review the major hypotheses that have been proposed to explain the axial osmolality gradient in the interstitium of the renal inner medulla. 3) We summarize and expand on the SchmidtNielsen hypothesis that the contractions of the renal pelvocalyceal wall may provide an important energy source for concentration in the inner medulla. 4) We discuss the special properties of hyaluronan, a glycosaminoglycan that is the chief component of a gel-like renal inner medullary interstitial matrix, which may allow it to function as a mechanoosmotic transducer, converting energy from the contractions of the pelvic wall to an axial osmolality gradient in the medulla. These considerations set the stage for renewed experimental investigation of the urinary concentrating process and a new generation of mathematical models of the renal concentrating mechanism, which treat the inner medullary interstitium as a viscoelastic system rather than a purely hydraulic system. glycosaminoglycans; renal pelvis; vasopressin; hyaluronan IN STATES OF FLUID DEPRIVATION or nonrenal water loss, the kidney can conserve water while maintaining excretion of solutes. It does this by concentrating the solutes in the urine to osmolalities that markedly exceed the osmolality of plasma. A large number of studies, exemplified by the data shown in Fig. 1, have demonstrated that the urinary concentrating process is associated with the generation of a corticomedullary osmolality gradient in the medullary tissue, oriented with the maximum osmolality in the deepest part of the inner medulla, i.e., at the papillary tip. The classic micropuncture studies of Gottschalk and Mylle (17) have established that the medullary hypertonicity is due to solute accumulation in all structures in the medulla, including loops of Henle, vasculature, and collecting ducts. The high medullary interstitial osmolality provides a driving force for osmotic water flow across the collecting ducts, which are rendered permeable to water through the action of vasopressin (33). The high water permeability allows osmotic equilibration of urine with the medullary interstitial fluid.In 1959, Kuhn and Ramel (43) proposed a model to explain concentration of solutes in the renal medulla Address for reprint requests and other correspondence: M. A. Knepper,

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Section: Single Effect In the Collecting Ductmentioning

confidence: 99%

Concentration of solutes in the renal inner medulla: interstitial hyaluronan as a mechano-osmotic transducer

Knepper

Saidel

Hascall

et al. 2003

American Journal of Physiology-Renal Physiology

112

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“…Countercurrent Multiplication between A T L and IMCD As for the model of countercurrent multiplication system in the inner medulla, we adopted the mathematical model previously reported [5]. Since the details of the model have been reported else Interaction between Urine Concentration and Urea Excretion where, we will briefly summarize the essential features of this model.…”

Section: Model and Equationsmentioning

confidence: 99%

“…This leads to a dilution of the interstitial fluid, favoring the diffusion of NaCl and urea out of the ATL. The computer simulation study revealed that this sequence of events resulted in generation of osmotic gra dients along the axis of the renal medulla [5],…”

Section: Introductionmentioning

confidence: 98%

“…It has been well established that the accumulation of both sodium and urea in the renal medulla is critical for the urine con centrating mechanism [1], The accumulation of urea in the renal medulla is favorable for the extrusion of NaCl from the ascending thin limb of Henle's loop (ATL), facil itating the accumulation of NaCl in the inner medulla by the countercurrent multiplication system via passive transport mechanisms [2,3], In addition, urea accumula tion in the renal medulla is important for providing a pri mary driving force of water from the inner medullary col-lecting duct (IMCD) as proposed in the model of countercurrent multiplication system operated between the ATL and IMCD [4,5], According to this model, the primary driving force of the system is accounted for by the lower apparent reflection coefficient for urea of the IMCD as opposed to that for NaCl. The fluid of the interstitium consists of almost equal amount of NaCl and urea, where as the fluid of the IMCD mainly consists of urea.…”

Section: Introductionmentioning

confidence: 99%

“…To examine whether the urine concentrating capacity is operated under an optimal condition which allows suf ficient amount of urea excretion into the urine, we devel oped an objective function between urea excreting capaci ty and water excreting capacity by using the mathematical model for the countercurrent multiplication system pre viously reported [5]. By using this function, we conducted a computer analysis to search transport parameter values which give the optimal condition for both urine concen tration and urea excretion.…”

Section: Introductionmentioning

confidence: 99%

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Optimal Transport Parameters of the Inner Medullary Collecting Duct in Interaction between Urine Concentrating and Urea Excreting Mechanisms: A Computer Simulation Study

Hamada¹,

Taniguchi²,

Imai³

1996

Nephron

Self Cite

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Although the accumulation of urea in the renal medulla is essential for the formation of concentrated urine, it is also necessary for the kidney to excrete considerable amounts of urea into the urine as a waste product of protein degradation. Thus, the urine concentrating capacity is attained by the interaction with the efficiency of urea excretion. To seek the best condition for this phenomenon, we developed an objective function for evaluating urea excreting capacity relative to urine concentrating capacity by using a mathematical model consisting of components of the countercurrent multiplication system: the ascending thin limb, capillary network, and inner medullary collecting duct. The values of the objective functions were calculated as three-dimensional functions of transport parameters for the inner medullary collecting duct, including hydraulic conductivity, urea permeability, and reflection coefficient for urea. The results of the computer analysis revealed that the maximum value of the objective function was attained when values for transport parameters of the inner medullary collecting duct corresponded to those experimentally obtained values reported previously. We conclude that the maximum urine concentrating capacity is limited by the efficiency of urea excreting capacity of the kidney, and vice versa.

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Mathematical Models of the Mammalian Urine Concentrating Mechanism

Layton¹

2002

Membrane Transport and Renal Physiology

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Simulation of the Profile of Water, NaCl, and Urea Transport in the Countercurrent Multiplication System between Thin Ascending Limb and Inner Medullary Collecting Duct.

Cited by 4 publications

References 40 publications

Concentration of solutes in the renal inner medulla: interstitial hyaluronan as a mechano-osmotic transducer

Concentration of solutes in the renal inner medulla: interstitial hyaluronan as a mechano-osmotic transducer

Optimal Transport Parameters of the Inner Medullary Collecting Duct in Interaction between Urine Concentrating and Urea Excreting Mechanisms: A Computer Simulation Study

Mathematical Models of the Mammalian Urine Concentrating Mechanism

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