Effects of hyperkalemia and glycoside on thallium exchange in rabbit ventricle

The exchange characteristics of thallium-201 (201Tl) were studied using the isolated arterially perfused rabbit interventricular septum to gain insight into the mechanisms that govern its uptake and subsequent washout from myocardial tissue. The results were compared to potassium-42 (42K) exchange. Unlike 42K, the uptake and tissue washout exchange rates for 201Tl were not equal. The 201Tl washout exchange rate was slower than that for the uptake. Hyperkalemia increased the efflux of both 42K and 201Tl, but the increase in 201Tl efflux was not due to an increase in permeability, as was true for 42K, but to a hyperkalemia, induced increase in compartment size of exchangeable 201Tl. Acetylstrophanthidin (ACS) resulted in an increase in 201 Tl efflux similar to the increase in 42K efflux seen with ACS. However, ACS did not inhibit 201Tl influx, in contrast to the known inhibition of 42K influx. This indicated that influx of tracer amounts of 201Tl was not dependent on the sodium-potassium pump. A model of Tl exchange in rabbit ventricles is proposed.