Abstract
Inward rectifier K+ (Kir2) channels are critical for electrical excitability of cardiac myocytes. Here, we examine expression of Kir2 channels in the heart of three Gadiformes species, polar cod (Boreogadus saida) and navaga (Eleginus nawaga) of the Arctic Ocean and burbot (Lota lota) of the temperate lakes to find out the role of Kir2 channels in cardiac adaptation to cold. Five boreal freshwater species: brown trout (Salmo trutta fario), arctic char (Salvelinus alpinus), roach (Rutilus rutilus), perch (Perca fluviatilis) and pike (Esox lucius), and zebrafish (Danio rerio), were included for comparison. Transcript expression of genes encoding Kir2.1a, − 2.1b, − 2.2a, − 2.2b and − 2.4 was studied from atrium and ventricle of thermally acclimated or acclimatized fish by quantitative PCR. Kir2 composition in the polar cod was more diverse than in other species in that all Kir2 isoforms were relatively highly expressed. Kir2 composition of navaga and burbot differed from that of the polar cod as well as from those of other species. The relative expression of Kir2.2 transcripts, especially Kir2.2b, was higher in both atrium and ventricle of navaga and burbot (56–89% from the total Kir2 pool) than in other species (0.1–11%). Thermal acclimation induced only small changes in cardiac Kir2 transcript expression in Gadiformes species. However, Kir2.2b transcripts were upregulated in cold-acclimated navaga and burbot hearts. All in all, the cardiac Kir2 composition seems to be dependent on both phylogenetic position and thermal preference of the fish.
Highlights
Temperature is a critical environmental factor for ectothermic animals by determining the rate of biochemical reactions and physiological processes of organisms (Precht1 3 Vol.:(0123456789)Journal of Comparative Physiology B (2019) 189:735–749 et al 1955)
Recent findings suggest that the high temperature-induced depression of heart rate in fish may be caused by the failure of electrical excitation of the heart (Badr et al 2016; Vornanen 2016)
Several Kir2 paralogues were present in all studied species
Summary
Temperature is a critical environmental factor for ectothermic animals by determining the rate of biochemical reactions and physiological processes of organisms (Precht1 3 Vol.:(0123456789)Journal of Comparative Physiology B (2019) 189:735–749 et al 1955). Temperature is a critical environmental factor for ectothermic animals by determining the rate of biochemical reactions and physiological processes of organisms Most fishes are ectotherms and physiologically adapted to tolerate temperature changes within speciesspecific limits. High temperatures depress heart rate and cardiac output and thereby the aerobic performance of the fish (Eliason et al 2013; Farrell 2009). In terms of global warming, temperature-dependence of cardiac function might be critical for survival, distribution and abundance of fish in future climates. Recent findings suggest that the high temperature-induced depression of heart rate in fish may be caused by the failure of electrical excitation of the heart (Badr et al 2016; Vornanen 2016)
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