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First published online February 4, 2005
Journal of Experimental Biology 208, 587-594 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01456

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Challenges and intriguing problems in comparative renal physiology

William H. Dantzler

Department of Physiology, College of Medicine, University of Arizona, Tucson, AZ 85724-5051, USA

View larger version (88K): [in a new window]   Fig. 1. Scanning electronmicrograph of a single glomerulus from a superficial loopless (reptilian-type) avian glomerulus (Anna's hummingbird). Vessels are filled with microfil. Vessel coming into glomerulus from left is the afferent arteriole. Vessel leaving glomerulus on the right is the efferent arteriole. Glomerular capillary exists as a single loop of capillary. Scale bar, 10 µm. Unpublished picture courtesy of Eldon J. Braun.

View larger version (31K): [in a new window]   Fig. 2. Net fluid movement in isolated perfused snake proximal renal tubules. Composition of solution in lumen and bath in terms of sodium and chloride and of substitutes for them is shown at sides of figure for each experiment. Each bar represents the mean ± S.E.M. (N=6-13) of net fluid movement with lumen and bath compositions shown (Dantzler, 1978; based on data from Dantzler and Bentley, 1978a).

View larger version (13K): [in a new window]   Fig. 3. Model of net transepithelial urate transport in reptilian (snake) proximal tubules. Circle with solid arrow indicates either primary or secondary active transport. Broken arrows indicate transport down electrochemical gradient. For countertransport, solid arrow indicates movement against electrochemical gradient and broken arrow, movement down electrochemical gradient. Broken arrows with question marks indicate possible passive movements. A- indicates anion of unspecified nature. Apparent permeabilities of luminal PL and peritubular membranes (PP) are shown (Dantzler, 1996).

View larger version (25K): [in a new window]   Fig. 4. Model of net transepithelial urate transport in avian (chicken) proximal tubules, indicating both independent transport and transport via the tertiary active transport process for most other organic anions (e.g. PAH). The independent process may involve countertransport for some unknown anion. The PAH transport system, which may be shared by urate, involves countertransport of PAH (or urate) for -ketoglutarate (-KG2-) that is produced by intracellular metabolism or that has entered the cells via the sodium dicarboxylate cotransport system. Symbols denoting these processes have same meanings as in Fig. 3 (Dantzler, 1996).