The Physiological Basis for Altered Na⁺ and Cl^- Movement Across the Gills of Rainbow Trout (Oncorhynchus mykiss) in Alkaline (pH=9.5) Water

Authors

Michael P. Wilkie, Wilfrid Laurier UniversityFollow
Pierre Laurent, Mount Allison University
Chris M. Wood, Mount Allison UniversityFollow

Document Type

Article

Publication Date

1999

Department

Biology

Abstract

To test the hypothesis that internal ion imbalances at high pH are caused by altered branchial ion transporting capacity and permeability, radiotracers (²⁴Na⁺ and ³⁶Cl^-) were used to measure ion movements across the gills of intact rainbow trout (Oncorhynchus mykiss) during 3 d exposure to pH 9.5. At control pH (pH 8.0), the trout were in net ion balance, but by 8 h at high pH, 60%–70% reductions in Cl^- influx (Cl) and Na⁺ influx (J^Na/in) led to net Cl^- and Na⁺ losses of -200 µmol kg^-1 h^-1. Outflux (diffusive efflux plus renal ion losses) was not initially altered. By 72 h, net Cl^- balance was reestablished because of a restoration of J^Cl/in. Although J^Na/in remained 50% lower at this time, counterbalancing reductions in Na⁺ outflux restored net Na⁺ balance. One-substrate ion-uptake kinetics analyses indicated that reduced ion influx after 8 h at pH 9.5 was caused by 50% decreases in Cl^- and Na⁺ maximal transport rates (J^Cl/max, J^Na/max), likely reflecting decreased numbers of functional transport sites. Two-substrate kinetic analyses indicated that reduced internal HCO₃^- and H⁺ supply for respective branchial Cl^-/base and Na⁺/acid transport systems also contributed to lower J^Cl/in and, to a lesser extent, lower J^Na/in at pH 9.5. Recovery in in of J^Cl/in after 3 d accounted for restoration of Cl^- balance and max likely reflected increased numbers of transport sites. In contrast, J^Na/in remained 33% lower after 3 d, but a lower affinity of the max gills for Na⁺ (fourfold greater K^Na/m) accounted for the chronic m reduction in Na⁺ influx at pH 9.5. Thus, reestablishment of Cl^- uptake capacity and counterbalancing reductions in Na⁺ outflux allows rainbow trout to reestablish net ion balance in alkaline waters.

Comments

This article was originally published in Physiological and Biochemical Zoology, 72(3): 360-368. © 1999 The University of Chicago Press

Recommended Citation

Wilkie, Michael P.; Laurent, Pierre; and Wood, Chris M., "The Physiological Basis for Altered Na⁺ and Cl^- Movement Across the Gills of Rainbow Trout (Oncorhynchus mykiss) in Alkaline (pH=9.5) Water" (1999). Biology Faculty Publications. 47.
https://scholars.wlu.ca/biol_faculty/47