Theoretical effects of UTB urea transporters in the renal medullary microcirculation.
A mathematical model of transport in the renal medullary microcirculation was used to investigate the role of the UTB urea transporter expressed in descending vasa recta (DVR) endothelia and red blood cell (RBC) membranes. Our simulations suggest that UTB raises RBC and plasma and interstitial urea concentrations by facilitating radial diffusion of the solute and therefore serves to increase the contribution of urea to the corticomedullary osmolality gradient, assuming no secondary effects on tubular transport. However, by lowering transmural urea concentration gradients, UTB reduces water efflux from DVR through aquaporin-1 (AQP1) water channels, thereby decreasing plasma sodium concentration. The net result of these competing effects on the osmolality gradient depends on the fraction of filtered urea that is reabsorbed by vasa recta. We also found that the contribution of UTB to water transport across DVR and RBCs is negligible, even in the absence of AQP1. Our model predicts that UTB plays a significant role, however, in reducing the shrinking and swelling of RBCs as blood flows along the medulla.
Zhang
Wensheng
W
Department of Chemical and Biological Engineering, Tufts University, 4 Colby St., Medford, MA 02155, USA. wensheng.zhang@tufts.edu
Edwards
Aurélie
A
D000818:Animals; D051398:Aquaporin 1; D020346:Aquaporins / Q000378:metabolism / Q000502:physiology; D001160:Arterioles; D001789:Blood Group Antigens; D004730:Endothelium, Vascular / Q000378:metabolism; D004910:Erythrocyte Membrane / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism; D006801:Humans; D007679:Kidney Medulla / Q000098:blood supply*; D026901:Membrane Transport Proteins / Q000097:blood* / Q000378:metabolism; D008833:Microcirculation; D008954:Models, Biological; D009995:Osmosis; D010539:Permeability; D012079:Renal Circulation; D012964:Sodium / Q000378:metabolism; D014508:Urea / Q000378:metabolism; D014867:Water / Q000378:metabolism; D000096982:Urea Transporters
D051398:Aquaporin 1; D020346:Aquaporins; D001789:Blood Group Antigens; D026901:Membrane Transport Proteins; D012964:Sodium; D014508:Urea; D014867:Water; D000096982:Urea Transporters; C496020:AQP1 protein, human