| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
AJP - Renal Physiology, Vol 270, Issue 1 9-20, Copyright © 1996 by American Physiological Society
ARTICLES |
H. E. Layton, M. A. Knepper and C. L. Chou
Department of Mathematics, Duke University, Durham, North Carolina 27708-0320, USA. layton@math.duke.edu
The urine concentrating effect of the mammalian renal inner medulla has been attributed to countercurrent multiplication of a transepithelial osmotic difference arising from passive absorption of NaCl from thin ascending limbs of long loops of Henle. This study assesses, both mathematically and experimentally, whether the permeability criteria for effective function of this passive hypothesis are consistent with transport properties measured in long loops of Henle of chinchilla. Mathematical simulations incorporating loop of Henle transepithelial permeabilities idealized for the passive hypothesis generated a steep inner medullary osmotic gradient, confirming the fundamental feasibility of the passive hypothesis. However, when permeabilities measured in chinchilla were used, no inner medullary gradient was generated. A key parameter in the apparent failure of the passive hypothesis is the long-loop descending limb (LDL) urea permeability, which must be small to prevent significant transepithelial urea flux into inner medullary LDL. Consequently, experiments in isolated perfused thin LDL were conducted to determine whether the urea permeability may be lower under conditions more nearly resembling those in the inner medulla. LDL segments were dissected from 30-70% of the distance along the inner medullary axis of the chinchilla kidney. The factors tested were NaCl concentration (125-400 mM in perfusate and bath), urea concentration (5-500 mM in perfusate and bath), calcium concentration (2-8 mM in perfusate and bath), and protamine concentration (300 micrograms/ml in perfusate). None of these factors significantly altered the measured urea permeability, which exceeded 20 x 10(-5) cm/s for all conditions. Simulation results show that this moderately high urea permeability in LDL is an order of magnitude too high for effective operation of the passive countercurrent multiplier.
This article has been cited by other articles:
|
|
 |
|
  T. L. Pannabecker, W. H. Dantzler, H. E. Layton, and A. T. Layton Role of three-dimensional architecture in the urine concentrating mechanism of the rat renal inner medulla Am J Physiol Renal Physiol, November 1, 2008; 295(5): F1271 - F1285. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Abe, P. O'Connor, M. Kaldunski, M. Liang, R. J. Roman, and A. W. Cowley Jr. Effect of sodium delivery on superoxide and nitric oxide in the medullary thick ascending limb Am J Physiol Renal Physiol, August 1, 2006; 291(2): F350 - F357. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. A. Fenton, C.-L. Chou, H. Sowersby, C. P. Smith, and M. A. Knepper Gamble's "economy of water" revisited: studies in urea transporter knockout mice Am J Physiol Renal Physiol, July 1, 2006; 291(1): F148 - F154. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. T. Layton and H. E. Layton A region-based mathematical model of the urine concentrating mechanism in the rat outer medulla. I. Formulation and base-case results Am J Physiol Renal Physiol, December 1, 2005; 289(6): F1346 - F1366. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. T. Layton and H. E. Layton A region-based mathematical model of the urine concentrating mechanism in the rat outer medulla. II. Parameter sensitivity and tubular inhomogeneity Am J Physiol Renal Physiol, December 1, 2005; 289(6): F1367 - F1381. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. T. Layton, T. L. Pannabecker, W. H. Dantzler, and H. E. Layton Two modes for concentrating urine in rat inner medulla Am J Physiol Renal Physiol, October 1, 2004; 287(4): F816 - F839. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. L. Pannabecker, D. E. Abbott, and W. H. Dantzler Three-dimensional functional reconstruction of inner medullary thin limbs of Henle's loop Am J Physiol Renal Physiol, January 1, 2004; 286(1): F38 - F45. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. L. Pallone, M. R. Turner, A. Edwards, and R. L. Jamison Countercurrent exchange in the renal medulla Am J Physiol Regulatory Integrative Comp Physiol, May 1, 2003; 284(5): R1153 - R1175. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. M. Weinstein Mathematical models of renal fluid and electrolyte transport: acknowledging our uncertainty Am J Physiol Renal Physiol, May 1, 2003; 284(5): F871 - F884. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. A. Knepper, G. M. Saidel, V. C. Hascall, and T. Dwyer Concentration of solutes in the renal inner medulla: interstitial hyaluronan as a mechano-osmotic transducer Am J Physiol Renal Physiol, March 1, 2003; 284(3): F433 - F446. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Hervy and S. R. Thomas Inner medullary lactate production and urine-concentrating mechanism: a flat medullary model Am J Physiol Renal Physiol, January 1, 2003; 284(1): F65 - F81. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. E. Layton, J. M. Davies, G. Casotti, and E. J. Braun Mathematical model of an avian urine concentrating mechanism Am J Physiol Renal Physiol, December 1, 2000; 279(6): F1139 - F1160. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. L. Pannabecker, A. Dahlmann, O. H. Brokl, and W. H. Dantzler Mixed descending- and ascending-type thin limbs of Henle's loop in mammalian renal inner medulla Am J Physiol Renal Physiol, February 1, 2000; 278(2): F202 - F208. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. R. Thomas Cycles and separations in a model of the renal medulla Am J Physiol Renal Physiol, November 1, 1998; 275(5): F671 - F690. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Visit Other APS Journals Online |
