title: Temperature and sex dependent effects on cardiac mitochondrial metabolism in Atlantic cod (Gadus morhua L.).
abstract: To test the hypothesis that impaired mitochondrial respiration limits cardiac performance at warm temperatures, and examine if any effect(s) are sex-related, the consequences of high temperature on cardiac mitochondrial oxidative function were examined in 10°C acclimated, sexually immature, male and female Atlantic cod. Active (State 3) and uncoupled (States 2 and 4) respiration were measured in isolated ventricular mitochondria at 10, 16, 20, and 24°C using saturating concentrations of malate and pyruvate, but at a submaximal (physiological) level of ADP (200µM). In addition, citrate synthase (CS) activity was measured at these temperatures, and mitochondrial respiration and the efficiency of oxidative phosphorylation (P:O ratio) were determined at [ADP] ranging from 25-200µM at 10 and 20°C. Cardiac morphometrics and mitochondrial respiration at 10°C, and the thermal sensitivity of CS activity (Q10=1.51), were all similar between the sexes. State 3 respiration at 200µM ADP increased gradually in mitochondria from females between 10 and 24°C (Q10=1.48), but plateaued in males above 16°C, and this resulted in lower values in males vs. females at 20 and 24°C. At 10°C, State 4 was ~10% of State 3 values in both sexes [i.e. a respiratory control ratio (RCR) of ~10] and P:O ratios were approximately 1.5. Between 20 and 24°C, State 4 increased more than State 3 (by ~70 vs. 14%, respectively), and this decreased RCR to ~7.5. The P:O ratio was not affected by temperature at 200μM ADP. However, (1) the sensitivity of State 3 respiration to increasing [ADP] (from 25 to 200μM) was reduced at 20 vs. 10°C in both sexes (Km values 105±7 vs. 68±10μM, respectively); and (2) mitochondria from females had lower P:O values at 25 vs. 100μM ADP at 20°C, whereas males showed a similar effect at 10°C but a much more pronounced effect at 20°C (P:O 1.05 at 25μM ADP vs. 1.78 at 100μMADP). In summary, our results demonstrate several sex-related differences in ventricular mitochondrial function in Atlantic cod, and suggest that myocardial oxidative function and possibly phosphorylation efficiency may be limited at temperatures of 20°C or above, particularly in males. These observations could partially explain why cardiac function in Atlantic cod plateaus just below this species׳ critical thermal maximum (~22°C) and may contribute to yet unidentified sex differences in thermal tolerance and swimming performance.
authors.affiliation: Department of Biological Sciences, Idaho State University, 921 South 8th Avenue, Mail Stop 8007, Pocatello, ID 83209-8007, USA. Electronic address: rodnkenn@isu.edu.
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Rodnick
authors.affiliation: Department of Ocean Sciences, Memorial University of Newfoundland, St. John׳s, NL, Canada A1C 5S7.
authors.forename: A Kurt
authors.initials: AK
authors.lastname: Gamperl
authors.affiliation: Department of Ocean Sciences, Memorial University of Newfoundland, St. John׳s, NL, Canada A1C 5S7.
authors.forename: Gordon W
authors.initials: GW
authors.lastname: Nash
authors.affiliation: Department of Biological Sciences, University of Calgary, Calgary, AB, Canada T2N 1N4.
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Syme
mesh_terms: D000064:Acclimatization; D000818:Animals; D019069:Cell Respiration; D003080:Cold Temperature; D005260:Female; D048389:Gadus morhua / Q000378:metabolism / Q000502:physiology*; D006321:Heart / Q000502:physiology; D008297:Male; D008929:Mitochondria, Heart / Q000378:metabolism*; D010085:Oxidative Phosphorylation; D012737:Sex Factors
keywords: Mitochondria; Oxidative phosphorylation; Sex differences; Temperature; Thermal tolerance