SUBCELLULAR-DISTRIBUTION OF TECHNETIUM-99M-N-NOET IN RAT MYOCARDIUM

The aim of this study was to determine the subcellular distribution of bis(l-ethoxy N-ethyl)dithiocarbamato nitrido technetium(V) ((TcN)-Tc- 99m-NOEt) in rat heart by differential centrifugation techniques. Extr action of the activity from homogenized rat heart tissue was also perf ormed to assess whether myocardial retention might induce changes in t he chemical identity of the complex. Methods: Anesthetized rats were i ntravenously injected with (TcN)-Tc-99m-NOEt, the heart tissue was ext racted and homogenized and tissue fractions were obtained by different ial centrifugation. The efficiency of organelle separation was determi ned by assay of each centrifugal fraction using enzyme markers. Lactat e dehydrogenase (LDH), acid phosphatase (ACP), alkaline phosphatase (A LP) and 5'-nucleotidase (5'ND) activities were assayed using standard spectrophotometric methods. Succinic dehydrogenase (SDH) activity was determined using a rho-iodo-nitrotetrazolium-linked assay. Severe cell membrane and organelle disruption were induced by prolonging the homo genization time and their effect on the subcellular distribution of (T cN)-Tc-99m-NOEt was studied. The activity from homogenized heart tissu e was extracted using the Folch technique and analyzed by TLC and HPLC . Results: Most of the (TcN)-Tc-99m-NOEt activity was found to be asso ciated with the hydrophobic components of the cell. No evidence of spe cific association of activity with the cytosolic and mitochondrial com ponents was observed. Organelle and membrane cleavage did not cause re lease of activity into the cytosol. Approximately 90% of (TcN)-Tc-99m- NOEt activity was extracted from ventricular tissue and the chemical n ature of (TcN)-Tc-99m-NOEt was not altered by uptake by myocardium. Co nclusion: Cell membranes are the most apparent site of localization of (TcN)-Tc-99m-NOEt in heart tissue.