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Beta-adrenergic function in juvenile sockeye salmon hearts Goulding, Adam Taylor


Adult Fraser River sockeye salmon (Oncorhynchus nerka) show population level tailoring of their cardiorespiratory system specific to upriver migration challenges. My thesis sought to expand our knowledge to juvenile sockeye salmon populations by studying stimulation of their cardiac performance via β-adrenergic receptors. I made measurements of myocardial cell-surface β2-adrenoceptor density in fish hearts 14-times smaller than previously accomplished by modifying and validating the tritiated ligand technique. For the Chilko sockeye salmon population, smolts had about half the receptor density of adults, but still twice that of adult hatchery O. mykiss. With my new technique, cardiac receptor density can now be investigated in a much wider range of fish species and life stages. I also investigated the effects of acclimation temperature on myocardial β-adrenergic stimulation (βAS) in juvenile sockeye by studying in vitro ventricular preparations that developed maximum isometric tension over a range of pacing frequencies (a force-frequency relationship – FFR) at both 5 °C (0.2 – 0.8 Hz) and 14°C (0.2 – 1.6 Hz). I compared juveniles from the Chilko River and Weaver Creek populations raised in a common-garden laboratory rearing environment (captive-reared) and wild Chilko juveniles captured and acclimated to the laboratory environment (wild-reared). Under tonic βAS (0.01 µM isoprenaline), active tension at 5 °C was either unchanged by pacing frequency (both Chilko populations), or modestly biphasic FFR (Weaver), whereas at 14 °C all three study groups had a negative FFR. Maximal βAS (32 µM isoprenaline) at 0.2 Hz doubled active tension in all study groups and at both temperatures, and all study groups had a negative FFR independent of temperature. However, only at 14 °C was active tension under maximal βAS greater than under tonic βAS for the highest and physiologically relevant pacing frequencies. Importantly, other than the modest biphasic FFR of Weaver Creek, the FFR did not differ appreciably between juveniles of two Fraser River sockeye populations.

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