Increased ventricular stiffness and decreased cardiac function in Atlantic cod (Gadus morhua) at high temperatures

Abstract

We employed the work loop method to study the ability of ventricular and atrial trabeculae from Atlantic cod to sustain power production during repeated contractions at acclimation temperatures (10°C) and when acutely warmed (20°C). Oxygen tension (Po2) was lowered from 450 to 34% air saturation to augment the thermal stress. Preparations worked under conditions simulating either a large stroke volume (35 contractions/min rate, 8-12% muscle strain) or a high heart rate (70 contractions/min, 2-4% strain), with power initially equal under both conditions. The effect of declining Po2 on power was similar under both conditions but was temperature and tissue dependent. In ventricular trabeculae at 10°C (and atria at 20°C), shortening power declined across the full range of Po2 studied, whereas the power required to lengthen the muscle was unaffected. Conversely, in ventricular trabeculae at 20°C, there was no decline in shortening power but an increase in lengthening power when Po2 fell below 100% air saturation. Finally, when ventricular trabeculae were paced at rates of up to 115 contractions/min at 20°C (vs. the maximum of 70 contractions/min in vivo), they showed marked increases in both shortening and lengthening power. Our results suggest that although elevated heart rates may not impair ventricular power as they commonly do isometric force, limited atrial power and the increased work required to expand the ventricle during diastole may compromise ventricular filling and hence, stroke volume in Atlantic cod at warm temperatures. Neither large strains nor high contraction rates convey an apparent advantage in circumventing this.

Echocardiography and electrocardiography reveal differences in cardiac hemodynamics, electrical characteristics, and thermal sensitivity between northern pike, rainbow trout, and white sturgeon

“…Given that Hill et al () reported a 25% reduction in contractile force by Chinook salmon ventricle strips exposed to 10 mg/L metomidate, and the fact that we had to use an even higher concentration of metomidate to anesthetize white sturgeon (25 mg/L) in the current study, we assessed in supplementary experiments whether exposure to relevant concentrations of metomidate affected the in vitro contractile properties (capacity to produce work) of cardiac tissue in northern pike, rainbow trout and white sturgeon. The approach and apparatus used are as described in Syme, Gamperl, Nash, and Rodnick () and Roberts and Syme (, ). Briefly, fish were killed by a blow to the head followed by pithing; no anesthetic was used during euthanasia to allow assessment of contractile performance both with and without exposure to anesthetics.…”

“…The approach and apparatus used are as described in Syme, Gamperl, Nash, and Rodnick (2013) and Syme (2016, 2018).…”

Temperature-induced cardiac remodeling in fish

“…When the temperature of ventricular trabeculae from Atlantic cod was increased from 10 to 20°C, the amount of work required to lengthen the preparations nearly doubled ( Syme et al, 2013 ). The authors suggest that this was due to an increase in the resting tension of the muscle ( Syme et al, 2013 ).…”

“…When the temperature of ventricular trabeculae from Atlantic cod was increased from 10 to 20°C, the amount of work required to lengthen the preparations nearly doubled ( Syme et al, 2013 ). The authors suggest that this was due to an increase in the resting tension of the muscle ( Syme et al, 2013 ). Such a response could be caused by the increase in temperature enhancing the Ca 2+ sensitivity of the myofilament, thereby increasing the number of active cross-bridges during diastole ( Gillis et al, 2005 , 2000 , 2003b ; Gillis and Tibbits, 2002 ).…”

“…For simplicity, we have structured the Review around observations associated with cold acclimation. Historically, responses to cold acclimation have been the main experimental interest ( Bailey and Driedzic, 1990 ; Driedzic et al, 1996 ; Farrell, 1991 ; Haverinen and Vornanen, 2007 ; Keen et al, 1993 , 1994 ; Lurman et al, 2012 ); however, with rising temperatures becoming a global concern, there is increasing interest in the effect of warming ( Farrell et al, 1996 ; Farrell, 2002 ; Keen et al, 2016 ; Klaiman et al, 2011 ; Syme et al, 2013 ). Therefore, we have added a concluding section to discuss the specific implications of prolonged warm temperatures on fish heart function.…”