The mechanism of adsorption of Ga-67 citrate to cultured cells.

Gallium adsorption was investigated at various pH values, with and without chelating agents or buffers. Evidence was obtained that Ga-67 citrate was adsorbed to cells in a polymeric form at a certain pH. Adsorption of Ga-67 to cells and to a glass surface reached a maximum at pH 4.5. When Ga-67 solutions were centrifuged to separate the precipitate, the highest precipitated radioactivity was found at the stated pH. With the addition of chelating agents which interact strongly with gallium, the adsorption to either cells or a glass surface was stoichiometrically inhibited. No such inhibition occurred, however, when counter ions unbound to gallium were added. The amount of Ga-67 released from the cell depended on the pH, suggesting that most of the gallium is deposited on the cell surface. Our results support Glickson's conclusion that gallium citrate forms a polymer at a certain acidic pH, which results in an increased cellular uptake by unknown mechanisms, presumably by pynocytosis.