title: Subcellular distribution and analysis of technetium-99m-MIBI in isolated perfused rat hearts.
abstract: 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.
authors.affiliation: Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: P A
authors.initials: PA
authors.lastname: Carvalho
authors.forename: M L
authors.initials: ML
authors.lastname: Chiu
authors.forename: J F
authors.initials: JF
authors.lastname: Kronauge
authors.forename: M
authors.initials: M
authors.lastname: Kawamura
authors.forename: A G
authors.initials: AG
authors.lastname: Jones
authors.forename: B L
authors.initials: BL
authors.lastname: Holman
authors.forename: D
authors.initials: D
authors.lastname: Piwnica-Worms
mesh_terms: 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
chemical_list: D009570:Nitriles; D015609:Organotechnetium Compounds; D017256:Technetium Tc 99m Sestamibi