LAB26 - 259 A Pharmacological Examination of Na and Cl...

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259 A Pharmacological Examination of Na 1 and Cl 2 Transport in Two Species of Freshwater Fish Marion R. Preest 1, * Richard J. Gonzalez 2 Rod W. Wilson 3 1 Department of Biology, University of Miami, 1301 Memorial Drive, Coral Gables, Florida 33157; 2 Department of Biology, University of San Diego, 5998 Alcala ´ Park, San Diego, California 92110; 3 Department of Biological Sciences, Hatherly Laboratories, University of Exeter, Exeter EX4 4PS, United Kingdom Accepted 8/13/04 Electronically Published 3/1/05 ABSTRACT We examined branchial Na 1 and Cl 2 uptake in two species of stenohaline, freshwater ±sh (gold±sh and the Amazonian neon tetra). Kinetic analysis revealed that the two species had similar uptake capacities and af±nities for Na 1 and Cl 2 . However, while uptakes of Na 1 and Cl 2 ( and , respectively) by gold±sh Na Cl JJ in were completely inhibited at pH 4.5 and below, uptake in tetras was unaffected by pH down to 3.25. Examination of Cl 2 trans- port with blockers indicated that gold±sh and neon tetras utilize Cl 2 / exchange; SITS and SCN 2 inhibited Cl 2 uptake in 2 HCO 3 both species. In contrast, large differences in Na 1 transport were indicated between the species. In gold±sh, exposure to four Na 1 /H 1 exchange blockers, as well as the Na 1 channel blocker phenamil, strongly inhibited . Further, Na 1 and Cl 2 Na J uptake were strongly inhibited by the Na 1 /K 1 /Cl 2 cotransport inhibitor furosemide, as was in “Cl 2 -free” water and in Na Cl “Na 1 -free” water. This suggests the presence of multiple trans- porters and possibly even a direct linkage between the transport of Na 1 and Cl 2 in gold±sh. In contrast, none of these drugs strongly reduced Na 1 transport in neon tetras, which raises the possibility of a signi±cantly different Na 1 transport mechanism in this acid-tolerant species. * Corresponding author; present address: Joint Science Department, Claremont Colleges, 925 North Mills Avenue, Claremont, California 91711; e-mail: mpreest@jsd.claremont.edu. Physiological and Biochemical Zoology 78(2):259–272. 2005. q 2005 by The University of Chicago. All rights reserved. 1522-2152/2005/7802-3140$15.00 Introduction Relative to seawater, freshwater is an extremely variable me- dium, both spatially and temporally, in which to survive. For example, concentrations of ions such as Na 1 and Cl 2 can vary over 400-fold (from ! 10 m mol L 2 1 to 1 4 mmol L 2 1 ), and pH can range from ! 3.25 to 1 8. Temperature and dissolved oxygen and organic content can be similarly variable. These charac- teristics depend on both biotic and abiotic aspects of the local environment (McDonald and Rogano 1986). In the face of this variability, however, one feature remains the same. Organisms living in freshwater must deal with a continual loss of ions to the surrounding medium. For freshwater teleosts, maintenance of high internal concentrations of ions involves active uptake of Na 1 and Cl 2 across the gills in a two-step process. Both salts are ±rst transported across the apical membrane into the bran- chial epithelial cells and then transferred across the basolateral membrane into the blood. Many general aspects of the trans-
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LAB26 - 259 A Pharmacological Examination of Na and Cl...

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