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Journal of Experimental Biology 116,411-433 (1985)
Published by Company of Biologists 1985

Kinetics of Branchial Calcium Uptake in the Rainbow Trout: Effects of Acclimation to Various External Calcium Levels

S. F. PERRY 1 and C. M. WOOD 2

1 Department of Biology, University of Ottawa, 30 Somerset E., Ottawa, Ontario, Canada KIN 6NS.; Department of Biology, McMaster University1280 Main St W., Hamilton, Ontario, Canada L8S 4K1
2 Department of Biology, McMaster University1280 Main St W., Hamilton, Ontario, Canada L8S 4K1

Calcium uptake (JCain) in freshwater rainbow trout (Salmo gairdnen) under control conditions (external [Ca2+] ~= 1.8 mequivl–1, [NaCl] ~= 0.8 mequiv 1–1) occurred at approximately equal rates (12–15 µequiv kg–1 h–1) through the gills and the general body surface in vivo. The gut was not involved. Under the same conditions, in vitro branchial JCain in an isolated, saline-perfused head preparation was equal to that in vivo. The cells involved in JinCa are mainly located on lamellae rather than on filaments since 95 % of JinCa occurred across the arterio-arterial circulation of the gill. JinCa, in vitro, displayed Michaelis-Menten kinetics. Acclimation to low external [Ca2+] (50 µequiv 1–1; unchanged [NaCl]) for 1 day caused a five-fold stimulation of JinCa characterized by decreased Km and increased J max. Longer periods of low [Ca2+] acclimation resulted in changes of Jmax only. Jmax gradually returned towards control levels as acclimation time increased, but was still elevated after 30 days. Acclimation to low ambient [Ca2+] caused proliferation and increased exposure of lamellar chloride cells which were correlated with increased Jmax. Fish exposed to high external [Ca2+] (10 mequivl–1; unchanged [NaCl]) displayed reduced JinCa Similar changes in JinCa were observed during in vivo experiments. Plasma Ca2+ concentration remained constant regardless of external [Ca2+], while plasma Na+ and Cl– levels were transiently reduced at 1 day low [Ca2+] exposure but had recovered by 7 days. A possible role for cortisol in Ca2+ regulation is discussed based on observations of cortisol-stimulated lamellar chloride cell proliferation and JinCa, and elevated plasma [cortisol] in low-[Ca2+] acclimated fish.

Key words: Calcium uptake, gills, chloride cell, perfusion, cortisol

Accepted on October 29, 1984






© The Company of Biologists Ltd 1985