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Figure 3 Tumor necrosis factor alpha acutely depresses contractile activity and calcium transients of isolated adult rat cardiomyocytes. Cells were loaded with the calcium sensitive dye, fura-2, and exposed to 200 U/ml rat TNF alpha or diluent (control) for 30 min. Cells were then electrically stimulated to contract (1 HZ) and a video edge-detection system used to record diastolic cell length and contraction to determine fractional shortening. Cells were alternately illuminated at 340- and 380-nm light and emission of the fura-2 measured at 520-nm. The ratio of light emission from the two illuminating wavelengths was used to follow intracellular free calcium transients. (A) Fractional shortening (n = 30 each group). (B) Mean calcium transient amplitude (difference between peak systolic and peak diastolic 340/380 nm ratio; n = 40 per group). (Wagner, Combes, Janczewski, McTiernan and Feldman; unpublished data). Open square = control; solid square = TNF alpha 200 U/ml.