In vivo analysis of intracellular thallium-201 accumulation in skeletal muscle of the rat.

The specific accumulation of the K(+)-analogue Tl+ (201Tl+) in muscle after intramuscular injection was analysed by gamma spectrometry in vivo of rat hamstring muscles. A mixture (0.1 ml) of 201Tl+ (thallous+ chloride-) and 99mTc-pertechnetate- (Na+ pertechnetate-) was given, by which 99mTc-pertechnetate- served as a reference substance with negligible intracellular accumulation. After 30 min 8.9 +/- 5.8% of injected 99mTc-pertechnetate- remained in the muscle and 49 +/- 10% of 201Tl+ (+/- SD, n = 18). The difference between 201Tl+ and 99mTc-pertechnetate- at 30 min was taken as a measure of the intracellular 201Tl+ accumulation, which was 40% of the initial amount of 201Tl+. The half-time of the calculated intracellular 201Tl+ accumulation was 4.9 +/- 1.9 min. In the presence of ouabain (1.0 mM in the injectate) the intracellular 201Tl+ accumulation was 25 +/- 10% (n = 7), that is ouabain decreased the intracellular 201Tl+ accumulation by 38% (P = 0.0035). Non-radioactive Tl+ (1.0 mM Tl-acetate in the injectate) inhibited the uptake by 35% (P = 0.0013). Ouabain did not significantly affect the half-time for the Tl+ uptake. An increase in [K+] of the injectate from 0 to 5 mM had no significant effect. Insulin (0.2 units in the injectate) had no effect. It is concluded that the specific Tl(+)-accumulating properties of muscle fibres can be studied with the present in vivo technique, which can provide information about the Na-K-ATPase activity and the membrane potential of muscle fibres.