Uptake kinetics of technetium-99m-methoxyisobutylisonitrile and thallium-201 in adult rat heart endothelial and fibroblast-like cells in comparison to myocytes.

Endothelial and fibroblast-like cells comprise 5%-10% of total cardiac cell volume and are more resistant to hypoxia than cardiomyocytes. However, their role in the uptake of radiotracers used for myocardial perfusion imaging has largely been ignored. Net uptake of 201TI and 99mTc-hexakis-2-methoxyisobutylisonitrile (99mTc-sestamibi) by cultured rat heart endothelial and fibroblast-like cells and quiescent myocytes was examined. Over a 30-min period, endothelial cells continuously accumulated 99mTc-sestamibi. Initial 201TI accumulation paralleled that of 99mTc-sestamibi; however, after 7 min 201TI accumulation plateaued whereas there was continued slow accumulation of 99mTc-sestamibi. Net uptake of the two radiotracers by fibroblast-like cells was similar to that of 201TI by endothelial cells. In the quiescent myocytes, there was an initial accumulation of both tracers with 201TI net uptake quickly reaching a plateau, whereas 99mTc-sestamibi accumulation continued throughout the 30-min period reaching a level 15-fold greater than that for 201TI. Myocyte uptake of 99mTc-sestamibi was approximately eight times greater than by the endothelial cells when expressed either as activity per mg protein or activity per cell volume. Although significant uptake differences exist among the three cell types, the fact that there is uptake by endothelial and fibroblast-like cells should be considered during image interpretation, particularly in situations in which the hypoxia resistant endothelial and fibroblast-like cells might be the remaining healthiest cell types.