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Mechanisms of ion transport in Potamotrygon, a stenohaline freshwater elasmobranch native to the ion-poor blackwaters of the Rio Negro

Chris M. Wood^1,2,*, Aline Y. O. Matsuo^1,2, R. J. Gonzalez^1,3, Rod W. Wilson^1,4, Marjorie L. Patrick^1,5 and Adalberto Luis Val¹

¹ Laboratory of Ecophysiology and Molecular Evolution, National Institute for Amazon Research (INPA), Alameda Cosme Ferreira, 1756-Aleixo, 69083-000 Manaus, Amazonas, Brazil
² Department of Biology, McMaster University, 1280 Main St. West, Hamilton, Ontario, Canada L8S 4K1
³ Department of Biology, University of San Diego, 5998 Alcala Park, San Diego, CA 92110, USA
⁴ School of Biological Sciences, Hatherly Laboratories, University of Exeter, Exeter EX4 4PS, UK
⁵ Department of Cell Biology and Neuroscience, University of California, Riverside, CA 92521, USA

View larger version (21K): [in a new window]   Fig. 1. Kinetic relationships for Na+ (filled symbols) and Cl- (open symbols) influx rates in stingrays acclimated to either ion-poor Rio Negro water (soft water, triangles, N=7) or ion-rich hard water (circles, N=6). Values are means ± 1 S.E.M. There were no significant effects of acclimation water on the relationships. The lines shown represent the Michaelis—Menten equations derived from the mean values of Km (in µmoll-1) and Jmax (in µmol kg-1 h-1) for all fish in both treatments (N=13) as shown.

View larger version (14K): [in a new window]   Fig. 2. The relationships between Na+ efflux (JoutNa) and external Na+ concentration ([Na+]ext) in stingrays acclimated to either ion-poor Rio Negro water (soft water, triangles and solid line, N=7) or ion-rich hard water (circles and dashed line, N=6). Values are means ± 1 S.E.M. By ANOVA, the relationships (considering only the four lowest Na+ concentrations) are significantly different, with a specific significant difference (*P0.05) around 400 µmol l-1. The thicker line shows the uptake kinetic relationship for JinNa from Fig. 1, and the arrows mark the intersection points of balance where JinNa=JoutNa. Axes are drawn to the same scale as Fig. 3 to facilitate comparison.

View larger version (17K): [in a new window]   Fig. 3. The relationships between Cl- efflux (JoutCl) and external Cl- concentration ([Cl-]ext) in stingrays acclimated to either ion-poor Rio Negro water (soft water, triangles and solid line, N=7) or ion-rich hard water (circles and dashed line, N=6). Values are means ± 1 S.E.M. There was a specific significant difference between the two relationships (*P0.05) only around 300 µmol l-1. The thicker line shows the uptake kinetic relationship for JinCl from Fig. 1, and the arrows mark the intersection points of balance where JinCl=JoutCl.

View larger version (22K): [in a new window]   Fig. 4. The influence, in stingrays acclimated to ion-poor Rio Negro water, of acute exposure to pH 4.0 for 2 h, followed by recovery at control pH 6.1 for 2 h, on (A) unidirectional (Jin, Jout) and net flux rates of Na+ (open bars) and Cl- (hatched bars) and (B) net ammonia flux rates (Jamm; filled bars). Values are means ± 1 S.E.M. (N=5). Standard errors have been omitted from net Na+ and Cl- net flux rates (shaded bars) for clarity as they sometimes overlap those of the unidirectional flux rates. Positive (upward) values represent uptake into the fish; negative (downward) bars represent losses from the fish. Asterisks indicate means significantly different (*P0.05) from the corresponding control mean.

View larger version (24K): [in a new window]   Fig. 5. The influence, in stingrays acclimated to ion-poor Rio Negro water, of (A) amiloride (10-4 mol l-1) and (B) DIDS (2x10-5 mol l-1) on unidirectional (Jin, Jout) and net flux rates of Na+ (open bars) and Cl- (hatched bars) during three successive 2 h periods. Values are means ± 1 S.E.M. (N=5). Other details as in the legend of Fig. 4.

View larger version (25K): [in a new window]   Fig. 6. The influence, in stingrays acclimated to ion-poor Rio Negro water, of (A) HMA (4x10-5 mol l-1) and (B) phenamil (4x10-5 mol l-1) on unidirectional (Jin, Jout) and net flux rates of Na+ (open bars) and Cl- (hatched bars) during three successive 2 h periods. Values are means ± 1 S.E.M. (N=5). Other details as in the legend of Fig. 4.

View larger version (16K): [in a new window]   Fig. 7. The influence, in stingrays acclimated to ion-poor Rio Negro water, of (A) DIDS (10-4 mol l-1), (B) SITS (10-4 mol l-1), (C) DPC (10-4 mol l-1) and (D) thiocyanate (10-4 mol l-1) on unidirectional (Jin; open bars) and net (filled bars) flux rates of Cl- during three successive 2 h periods. Values are means ± 1 S.E.M. (N=5). Other details as in the legend to Fig. 4.

View larger version (29K): [in a new window]   Fig. 8. The influence, in stingrays acclimated to ion-poor Rio Negro water, of (A) amiloride (10-4 mol l-1), (B) HMA (4x10-5 mol l-1) and (C) phenamil (4x10-5 mol l-1) on net ammonia flux rates (Jamm). Values are means ± 1 S.E.M. (N=5). Other details as in the legend of Fig. 4.