Microprobe analysis of technetium-mibi accumulation in cultured heart cell mitochondria: Correlation of structure and membrane potential

Abstract

Hexakis (methoxyisobutylisonitrile)99mTechnetium (Tc-MTBI) is a gamma emitting radiopharmaceutical currently in clinical use for evaluating myocardial perfusion. Because Tc-MIBI exists as a lipophilic cation with a single positive charge, it has been shown to concentrate in mitochondria in response to membrane potential in a Nernstian fashion similar to rhodamine 123. Use of electron probe x-ray microanalysis (EPXMA) for localization and quantitation of the element technetium in mitochondria and calculation of membrane potential allows correlation for the first time between mitochondrial structure and membrane potential in intact cells.Heart cells from 11-day-old chick embryos were cultured into spherical aggregates 50 -100 μm in diameter after Ebihara et al. Aggregates were then incubated for 60 minutes in HEPES balanced buffer salt solution containing either 0, 36,72, or 144 μMTc99-MIBI as well as 20 mCi metastable Tc99m-MIBI. Some aggregates were prepared for conventional fixation and subsequent electron microscopic evaluation, while other aggregates were plunge frozen in liquid propane and cryosectioned for quantitative EPXMA.