title: Effects of prolonged anoxia on electrical activity of the heart in crucian carp (Carassius carassius).
abstract: The effects of sustained anoxia on cardiac electrical excitability were examined in the anoxia-tolerant crucian carp (Carassius carassius). The electrocardiogram (ECG) and expression of excitation-contraction coupling genes were studied in fish acclimatised to normoxia in summer (+18°C) or winter (+2°C), and in winter fish after 1, 3 and 6 weeks of anoxia. Anoxia induced a sustained bradycardia from a heart rate of 10.3±0.77 beats min-1to 4.1±0.29 beats min-1(P<0.05) after 5 weeks, and heart rate slowly recovered to control levels when oxygen was restored. Heart rate variability greatly increased under anoxia, and completely recovered under re-oxygenation. The RT interval increased from 2.8±0.34 s in normoxia to 5.8±0.44 s under anoxia (P<0.05), which reflects a doubling of the ventricular action potential (AP) duration. Acclimatisation to winter induced extensive changes in gene expression relative to summer-acclimatised fish, including depression in those genes coding for the sarcoplasmic reticulum calcium pump (Serca2a_q2) and ATP-sensitive K+channels (Kir6.2) (P<0.05). Genes of delayed rectifier K+(kcnh6) and Ca2+channels (cacna1c) were up-regulated in winter fish (P<0.05). In contrast, the additional challenge of anoxia caused only minor changes in gene expression, e.g. depressed expression of Kir2.2b K+channel gene (kcnj12b), whereas expression of Ca2+(cacna1a, cacna1c and cacna1g) and Na+channel genes (scn4a and scn5a) was not affected. These data suggest that low temperature pre-conditions the crucian carp heart for winter anoxia, whereas sustained anoxic bradycardia and prolongation of AP duration are directly induced by oxygen shortage without major changes in gene expression.
authors.affiliation: University of Eastern Finland, Department of Environmental and Biological Sciences, PO Box 111, Joensuu 80101, Finland.
authors.forename: Elisa
authors.initials: E
authors.lastname: Tikkanen
authors.affiliation: University of Eastern Finland, Department of Environmental and Biological Sciences, PO Box 111, Joensuu 80101, Finland.
authors.forename: Jaakko
authors.initials: J
authors.lastname: Haverinen
authors.affiliation: Multidisciplinary Cardiovascular Research Centre, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, UK.
authors.forename: Stuart
authors.initials: S
authors.lastname: Egginton
authors.affiliation: University of Eastern Finland, Department of Environmental and Biological Sciences, PO Box 111, Joensuu 80101, Finland.
authors.forename: Minna
authors.initials: M
authors.lastname: Hassinen
authors.affiliation: University of Eastern Finland, Department of Environmental and Biological Sciences, PO Box 111, Joensuu 80101, Finland matti.vornanen@uef.fi.
authors.forename: Matti
authors.identifier: 0000-0003-0953-1425
authors.initials: M
authors.lastname: Vornanen
mesh_terms: D000064:Acclimatization; D000200:Action Potentials; D000222:Adaptation, Physiological; D000693:Anaerobiosis; D000818:Animals; D002347:Carps / Q000235:genetics / Q000502:physiology*; D004562:Electrocardiography; D005786:Gene Expression Regulation; D006321:Heart / Q000502:physiology; D006339:Heart Rate; D010100:Oxygen / Q000378:metabolism*; D012621:Seasons
chemical_list: D010100:Oxygen
keywords: Anoxia tolerance; Bradycardia; Electrical excitability; Excitation–contraction coupling; Fish heart; Seasonal acclimatisation