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This Article Full Text Full Text (PDF) All Versions of this Article: 297/2/F537    most recent 90497.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Web of Science (1) Google Scholar Articles by Chen, J. Articles by Layton, A. T. PubMed PubMed Citation Articles by Chen, J. Articles by Layton, A. T.

A mathematical model of O₂ transport in the rat outer medulla. II. Impact of outer medullary architecture

¹Department of Chemical and Biological Engineering, Tufts University, Medford, Massachusetts; and ²Department of Mathematics, Duke University, Durham, North Carolina

Submitted 19 August 2008 ; accepted in final form 23 April 2009

we extended the region-based mathematical model of the urine-concentrating mechanism in the rat outer medulla (OM) developed by Layton and Layton (Am J Physiol Renal Physiol 289: F1346–F1366, 2005) to examine the impact of the complex structural organization of the OM on O₂ transport and distribution. In the present study, we investigated the sensitivity of predicted PO₂ profiles to several parameters that characterize the degree of OM regionalization, boundary conditions, structural dimensions, transmural transport properties, and relative positions and distributions of tubules and vessels. Our results suggest that the fraction of O₂ supplied to descending vasa recta (DVR) that reaches the inner medulla, i.e., a measure of the axial PO₂ gradient in the OM, is insensitive to parameter variations as a result of the sequestration of long DVR in the vascular bundles. In contrast, O₂ distribution among the regions surrounding the vascular core strongly depends on the radial positions of medullary thick ascending limbs (mTALs) relative to the vascular core, the degree of regionalization, and the distribution of short DVR along the corticomedullary axis. Moreover, if it is assumed that the mTAL active Na⁺ transport rate decreases when mTAL PO₂ falls below a critical level, O₂ availability to mTALs has a significant impact on the concentrating capability of the model OM. The model also predicts that when the OM undergoes hypertrophy, its concentrating capability increases significantly only when anaerobic metabolism supports a substantial fraction of the mTAL active Na⁺ transport and is otherwise critically reduced by low interstitial and mTAL luminal PO₂ in a hypertrophied OM.

region-based model; medullary thick ascending limbs; red blood cells; active sodium transport