Effects of exercise on kinetics and distribution K-43 and Tl-201 in isolated myocardium: concise communication

Kinetics and distribution K-43 and Tl-201 were studied in isolated myocardial tissue from rats to assess the effects of exercise. Rats in some groups were forced to swim for 2 h; immediately after swimming, they were injected with 0.2 mCi of 43KCl or 201TlCl; at 0.5 or 3 hr after injection they were killed and a myocardial segment was obtained and subjected to washout with nonradioactive Krebs fluid in a special chamber. In control groups (rested) the exercise was omitted. A three-comparatment model (extracellular, main intracellular, and subcellular) was used; transport rate constants and relative compartment sizes were determined. The most striking finding was the unchangeability of K-43 parameters with regard to experimental condition. On the other hand, Tl-201 parameters were modified by exercise and sampling time. Notable differences between K-43 and Tl-201 kinetics were found. The hypothesis that alterations at the cellular level may affect regional myocardial distribution of a radionuclide is discussed