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Fig. 1. Experimental design involving additions of D-glucose, inotropes and metabolic inhibitors to cardiac tissue in vitro. In all experiments, ventricle strips from rainbow trout were incubated for 60 min in either glucose or glucose-free media and electrically stimulated (0.5 Hz) at 14°C. (A) Glucose dose-response. Zero glucose reflects control ventricle strips remaining in glucose-free media for the entire experiment. (B) Combined effects of glucose (5 mmol l^-1) and inotropes: T (0.3 µmol l^-1) in males; E2 (1 nmol l^-1) in females; and Epi (1 µmol l^-1) or Ca²⁺_o (5 mmol l^-1) in both sexes. (C) Effects of inotropes mentioned above and caffeine (8 mmol l^-1), with and without glucose. (D) Effects of inotropes in ventricle strips pretreated with inhibitors iodoacetate (IAA) (0.4 mmol l^-1) or ryanodine (10 µmol l^-1). (E) Original recording of isometric twitch force in ventricular muscle strips from a male rainbow trout. After ventricle strips were stretched to optimal length (90% L_max) and after mechanical stabilization for 60 min, glucose (5 mmol l^-1) was added to one strip and the other remained glucose-free (control) for 60 min. The extent of stored Ca²⁺ in the sarcoplasmic reticulum was determined by post rest potentiation (PRP). Stimulation of ventricle strips was discontinued for 5 min, prior to PRP measurements. PRP was higher in glucose-treated ventricle strips when compared with the corresponding glucose-free control. Values are means ± s.e.m. (N=6-11 strips per group).

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