Fig. 4.

Atrial tissue remodelling. Representative haematoxylin and eosin (H&E)-stained atrial tissue sections for a cold-acclimated (CA, left) and warm-acclimated (WA, right) rainbow trout. Quantification of b myocyte bundle cross-sectional area and c extra-bundular sinus with temperature acclimation. For measurement of cross-sectional area of myocyte bundles, three separate image montages were taken along transects across the full diameter of the cross section on each tissue section. In each image, trabeculations were chosen for measurement only if they were in the transverse plane, i.e. the image showed a cross section of the trabeculations making it circular in appearance. For EBS space, the non-tissue area of each image was measured. d mRNA expression of markers of muscle growth (VMHC, MLP and SMLC2), hyperplasia (PNCA) and angiogenesis (VEGF). e Hypertrophic markers (ANP and BNP) and regulator of the pro-hypertrophic NFAT signalling pathway (RCAN1). In b–e, cold (5 °C; blue), control (10 °C; green) and warm (18 °C; red) acclimation. n = 10 fish per acclimation group; 3 replicates for each animal were averaged for both histology and qPCR. Values presented are mean ± S. E. Significance was assessed by GLM with Holm-Sidak post hoc test. Significance between groups is shown by dissimilar letters (P < 0.05). Supplementary Table 1 contains the list of specific primers used for quantitative real-time PCR