Isometric force and [Ca2+]
measured from LV trabeculae. Isometric force and [Ca2+]i were measured simultaneously in LV trabeculae at 37°C, 5 Hz stimulation frequency and 1.5 mmol/L [Ca2+]o, conditions that are close to physiological. (A) Exemplary traces of Ca2+ transients (fura-2/AM 340/380 ratio) and corresponding isometric stress (force normalized to the corresponding muscle’s cross-sectional area) averaged over a number of cardiac cycles in representative trabeculae from the 3 experimental groups, which typify those used for data analysis. Inserted figures are corresponding raw traces of Ca2+ transients and corresponding isometric stress. (B) Averaged values from 7 trabeculae in each experimental group for (i) the Ca2+ transient, (ii) isometric stress and (iii) phase plots of Ca2+ transients and corresponding isometric stress. Diabetic rats showed decreased responsiveness to Ca2+, as indicated by the rightward shift of the relaxation phase (iii) and TETA-treatment prevented development of this defect.