Subcellular distribution and analysis of technetium-99m-MIBI in isolated perfused rat hearts.
To address the apparent discrepancy between cultured cells and whole heart preparations, Langendorff-perfused rat hearts loaded with hexakis (2-methoxyisobutyl isonitrile) technetium (I) (99mTc-MIBI) were fractionated by a standard differential centrifugation method and fractional contents of 99mTc-MIBI were correlated with the mitochondrial marker, malate dehydrogenase (MDH), and mitochondrial substrates. The "cytosolic" fraction nominally contained 89% +/- 3% of total 99mTc-MIBI, but also contained 91% +/- 1% of total MDH activity by this method. Chromatographic analysis of activity in the "cytosolic" fraction demonstrated greater than 95% of the agent was present as the original free cationic complex; binding to a small molecular weight cytosolic protein was not involved in localization. Addition of the mitochondrial uncoupler CCCP (5 microM) to both "mitochondrial" and "cell fragment" pellets released up to 84% +/- 8% of 99mTc-MIBI content and addition of the mitochondrial substrate succinate (10 microM) in the presence of rotenone (1 microM) enhanced 99mTc-MIBI content by up to 139% +/- 52% over the control. These correlative data from rat hearts indicate that approximately 90% of 99mTc-MIBI activity in vivo is associated with mitochondria in an energy-dependent manner as a free cationic complex, but migrates during fractionation/centrifugation.
Carvalho
P A
PA
Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115.
Chiu
M L
ML
Kronauge
J F
JF
Kawamura
M
M
Jones
A G
AG
Holman
B L
BL
Piwnica-Worms
D
D
D000818:Animals; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D009570:Nitriles / Q000493:pharmacokinetics*; D015609:Organotechnetium Compounds / Q000493:pharmacokinetics*; D051381:Rats; D011919:Rats, Inbred Strains; D013347:Subcellular Fractions / Q000378:metabolism*; D017256:Technetium Tc 99m Sestamibi
D009570:Nitriles; D015609:Organotechnetium Compounds; D017256:Technetium Tc 99m Sestamibi