Subcellular [3H]digoxin distribution after temporary myocardial ischemia in dogs

Following a 90-min coronary occlusion and 2 h reperfusion in 11 dogs, total tissue and subcellular distributions of [3H]digoxin in non-ischemic and various ischemic tissues were measured. In the non-ischemic tissue, [3H]digoxin in the crude homogenate, sediments obtained from 1000 X g, 10000 X g and 100000 X g centrifugations, and final supernatant fraction were 0.70 +/- 0.05, 0.79 +/- 0.05, 0.64 +/- 0.04, 3.87 +/- 0.34 and 0.19 +/- 0.02 ng/mg protein, respectively. As in studies with total tissue [3H]digoxin uptake, a reciprocal correlation was observed in reduction of digoxin binding in the crude homogenates and the 1000 X g sediments with increasing severity of ischemic injury estimated from the loss of nitro-blue-tetrazolium (NBT) stain. A 20% and 80% loss of NBT stain was associated with a 13.3% and 63.5% decrease in digoxin binding, respectively. In contrast, digoxin binding in the 10000 X g sediments increased progressively with the severity of ischemia. No significant change was observed in the final supernatant fraction. Digoxin binding in the 100000 X g sediments, which generally represent specific binding and which are associated with the pharmacologic effects, was not altered in tissues with a loss of NBT stain up to 50%. In fact, a loss of 80% NBT was associated with only a 33.9% decrease in digoxin binding. Thus, it appears that measurement of total tissue digoxin uptake does not provide an accurate measure of the effects of acute ischemia on specific digoxin binding. The ability of the peri- and moderately ischemic tissues (with less than 50% loss of NBT stain) to specifically bind digitalis was not altered after temporary myocardial ischemia.