Continuous fluorimetric assessment of the changes in cytoplasmic calcium concentration during exposure of rat isolated myocardium to conditions of simulated ischaemia.

1. The cytoplasmic calcium concentration ([Ca]c) of rat isolated atrial myocardium was assessed with the dye indo-1. Dye-loaded atria were superfused with physiological salt solution and excited with radiation at 360 nm, while epifluorescence emissions were collected simultaneously at 400 nm and 500 nm. The ratio of these emissions was used as a measure of [Ca]c. 2. Dye-loaded atria showed a phasic rise and fall in [Ca]c with each applied electrical pacing stimulus. The amplitudes of systolic increments in tension and [Ca]c were augmented by the presence of isoprenaline. 3. Atria superfused with a solution the composition of which resembled that found extracellularly in regions of ischaemia rapidly lost systolic increments in tension and [Ca]c, while end-diastolic [Ca]c and tension gradually rose. 4. The presence of lactate (20 mM) or flufenamate (5 microM) in the superfusate during simulated ischaemia aggravated the rises in both end-diastolic tension and end-diastolic [Ca]c. Inclusion in the superfusate of sulphinpyrazone (50 microM) or glucose (20 mM) protected against some of the deleterious effects of lactate seen during simulated ischaemia.