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

The specific accumulation of the K⁺-analogue TI⁺(²⁰¹Tl⁺) in muscle after intramuscular injection was analysed by gamma spectrometry in vivo of rat hamstring muscles. A mixture (0.1ml) 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 ²⁰¹TI⁺. The half-time of the calculated intracellular ²⁰¹TI⁺ 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 TI⁺ (1.0 mM TI-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 TI⁺-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.