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 99mTc-MIBI and 99mTc-Tetrofosmin were taken up by smooth muscle cells in similar pharmacokinetic patterns, but their accumulation reflected a different meaning for cell viability. (author)