Urate transport in homarus americanus hepatopancreas: studies on membrane vesicles and r-cells. Nies, A. T., R. K. H. Kinne, E. Kinne-Saffran, and M. K. Grieshaber. Universit[umlaut]at D[umlaut]usseldorf, Universit[umlaut]atsstr. 1, Institut f[umlaut]ur Tierphysiologie, 40225 D[umlaut]usseldorf, Germany, ph. 0211-3114990, fax 0211-3113897, Max-Planck-Institut f[umlaut]ur molekulare Physiologie, P.O. Box 102664, 44026 Dortmund, Germany, ph. 0231-1206480, fax 0231-1206464, Mount Desert Island Biological Laboratories, Old Bar Harbour Road, Salsbury Cove, Maine 04672, USA, ph. 207-288-3605, fax 207-288-2130
APStracts 2:0079R, 1995.
[2-14C]urate uptake was studied in hepatopancreatic basolateral membrane vesicles and in R-cell suspensions of the American lobster by Millipore filtration techniques. Unspecific binding of urate to the vesicular membrane was 25.5+/-3.0% of equilibrium. Vesicular uptake showed a diffusional and a saturable component (KM 0.37+/-0.04 mM, vmax 16.5+/-1.2 pmol urate/mg protein/s). [2-14C]urate uptake was significantly trans-stimulated by urate. Purine analogues, probenecid, p-aminohippuric acid, pyrazinoic and oxonic acid cis -inhibited urate transport. Urate uptake was not affected by Na+ or K+ transmembrane gradients but stimulated by 1mM 2-oxoglutarate at the cis-side in Na+ containing media. Cellular urate uptake was inhibited by pyrazinoic acid. Uptake was saturable (KM 0.53+/-0.11 mM, vmax 3.7+/-0.4 pmol urate/mg protein/s) and Na+ independent. However, 2 -oxoglutarate stimulated uptake in Na+ containing media. These results suggest that urate uptake across the basolateral membrane occurs via a specific, Na+ independent transport system that may operate in the exchange mode accepting 2-oxoglutarate as counter-transported substrate. In vivo, urate uptake thereby would be a tertiary active system driven by a 2-oxoglutarate gradient established across the cell membrane by the operation of a Na+/2-oxoglutarate co-transport system. 

Received 31 March 1994; accepted in final form 24 February 1995.
APS Manuscript Number R160-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on  6 April 1995.