Comparison of cationic myocardial perfusion agents: Characteristics of accumulation in cultured smooth muscle cells

The uptake and washout kinetics of two cationic lipophilic ^99mTc- labeled myocardial perfusion agents. ^99mTc-methoxyisobutylisonitrile (^99mTc-MIBI) and ^99mTc-1, 2-bis[bis-(2-ethoxyethyl)-phosphino]ethane (^99mTc-Tetrofosmin), were studied in cultured smooth muscle cells and compared to the conventional myocardial perfusion agent, ²⁰¹Tl. Both ^99mTc-MIBI and ^99mTc-Tetrofosmin had a 4-fold greater uptake than ²⁰¹Tl, and they were washed out of cells through similar kinetics which had slower rates than ²⁰¹Tl. Incubation with metabolism inhibitors had a modest influence on the uptake of these two ^99mTc-labeled agents, although their extent and inhibited sites were slightly different. Ion transport inhibitors did not affect the uptake of ^99mTc-MIBI, although the ^99mTc- Tetrofosmin uptake was slightly inhibited when the Ca²⁺ channel was blocked. Our studies indicate that ^99mTcMIBI and ^99mTc-Tetrofosmin were taken up by smooth muscle cells in similar pharmacokinetic patterns, but their accumulation reflected a different meaning for cell viability.