Effects of temperature and adrenaline on the atrial myocardium of the cultured Atlantic salmon (Salmo salar)

The effects of acute temperature changes (2–17°C) on myocardial contractility with or without adrenergic activation were studied in the isolated spontaneously beating atrium of the Atlantic salmon (Salmo salar) reared at 8°C. The atrial frequency was markedly elevated (from 7 to 46 beats/min) by the rise in temperature from 2–17°C. Both the time to peak tension and to relaxation time were shortened. In contrast, the temperature effect on the maximal tension was modest. Exposure to exogenous adrenaline (1.1 nM–11 μM) resulted in a substantial enhancement of the maximal tension, notably at 2°C, while potentiation of the frequency at 2, 8 and 14°C, was less pronounced. The apparent affinity (pD₂) for adrenaline on the chronotropy was higher at 8 and 14°C than at 2°C. For the inotropic responses pD₂ was highest at the acclimation temperature (8°C). By comparison with data for the rainbow trout (Oncorhynchus mykiss) obtained by the same experimental design (Ask et al. 1981), species differences were apparent both in temperature dependence of contractile parameters and in their adrenergic activation. The Q₁₀ for the frequency in absence of adrenaline was higher in the salmon than in the trout for the temperature interval 2–17°C. The apparent affinities for adrenaline for the frequency at 8°C and 14°C and for the maximal tension responses at 2°C and 8°C were also highest for the salmon atrium.