The effect of temperature acclimation on the force-frequency relationship and adrenergic sensitivity of the ventricle of
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ORIGINAL PAPER
The effect of temperature acclimation on the force‑frequency relationship and adrenergic sensitivity of the ventricle of two populations of juvenile sockeye salmon A. T. Goulding1 · A. P. Farrell1,2 Received: 26 January 2020 / Revised: 8 June 2020 / Accepted: 15 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract We tested the hypothesis that cardiorespiratory differences known to exist among adult sockeye salmon populations also exist in the juveniles. To test this hypothesis, we compared cardiac contractility and adrenergic responsiveness of juvenile sockeye salmon from two geographically isolated populations that were reared from eggs under common garden conditions and at two acclimation temperatures (5 °C and 14 °C). However, we found no substantive differences in the force-frequency response (FFR) and the cardiac pumping capacity of juveniles from Weaver Creek and Chilko River populations, even when we considered wild-reared juveniles from one of the populations. An unexpected discovery for all fish groups at 5 °C was a rather flat FFR during tonic β-adrenergic stimulation (βAR) stimulation. Curiously, while active tension nearly doubled with maximum βAR stimulation at low pacing frequencies for all fish groups, a negative FFR with maximum βAR stimulation meant that this inotropic benefit was lost at the highest pacing frequency (0.8 Hz). Active tension with tonic βAR stimulation was similar at 14 °C, but maximum pacing frequency doubled and all fish groups displayed a modest negative FFR. Maximum βAR stimulation again doubled active tension and this benefit was retained even at the highest pacing frequency (1.6 Hz) at 14 °C. Even though subtle population differences were apparent for the FFR and pumping capacity, their biological significance is unclear. What is clear, however, is that the cardiac pumping capacity of juvenile sockeye would benefit more from βAR stimulation swimming at 15 °C than when swimming at 5 °C. Keywords Force-frequency response · Heart · Temperature · Catecholamine · Juvenile · β-adrenoceptors
Introduction Temperature has an overarching effect on the force of contraction of fish hearts (Farrell and Smith 2017). Probably the most important cardiac effects are the pervasive increase in heart rate when fishes are warmed (e.g., Randall 1968; Lefrançois and Claireaux 2003; Sandblom and Axelsson 2011; Farrell 2016) and the numerous, well-studied cardiac Communicated by Bernd Pelster. * A. T. Goulding [email protected] 1
Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, BC V6T 1Z4, Canada
Faculty of Land and Food Systems, University of British Columbia, 2357 Main Mall, Vancouver, BC V6T 1Z4, Canada
2
changes that can accompany temperature acclimation (see recent reviews by Eliason and Anttila 2017; Vornanen 2017; Farrell and Smith 2017). A change in heart rate can directly affect the force of cardiac contraction, an inter-dependence that has been characterized in various fish species by me
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