Uptake mechanism of technetium-99m-d, 1-HMPAO in cell cultures of the dissociated postnatal rat cerebellum.

The accumulation and retention mechanisms of 99mTc-d, 1-hexamethylpropyleneamine oxime (99mTc-d, 1-HMPAO) were investigated in cultures of the dissociated rat cerebellum. Our experiments indicate a linear dependency of the uptake on incubation time and on the concentration of the radioligand. Upon chloroform extraction and distribution between the lipophilic and the hydrophilic phases, we located 69.1% of the retained radioactivity in the hydrophilic phase, 24.1% in a bound state and 6.8% in the lipophilic phase. The water-soluble, unbound radioactive contents of the cultures were identified as 99mTcO4- by HPLC analysis. Treatment of cultures with diethyl maleate (DEM) inhibited the accumulation of radioactivity along with a reduction of the GSH contents of the cultures. However, even in the absence of GSH, significant amounts of radioactivity were accumulated. DEM reduced the radioactive contents of cultures predominantly by diminishing the aqueous phase of the chloroform-extracted material. By contrast, the metabolic state, manipulated by treating the cultures with oligomycin B or 2,4-dinitrophenol, had no significant effect on the accumulation of radioactivity. Our experiments suggest two major mechanisms for the retention of radioactivity following the exposure of neuronal tissue to 99mTc-d, 1-HMPAO: Conversion of the lipophilic complex to the hydrophilic product, 99mTcO4-, and binding to non-diffusible cell components.