Calibration of [14C]plastic standards for quantitative autoradiography of [125I]labeled ligands with Amersham Hyperfilm beta-max.

The densitometric response of Hyperfilm beta-max (HFBM) to [14C]plastic standards was calibrated to tissue-equivalent concentrations of [125I]. Plastic sections with standard concentrations of [125I] and [14C] were apposed to HFBM for 1, 3, 5, and 9 days, with liver and muscle slices (20 microns thick) labeled with [125I]insulin. The relative optical densities (ROD = log 10 [1/gray level x 256(-1)] produced by [125I]- and [14C]plastic standards were converted to equivalent tissue [125I] concentrations (dpm/mm2). The response of HFBM to the [125I]- and [14C]plastic standards was similar (P less than 0.001). Standard curves of tissue [125I] (dpm/mm2) vs plastic [14C] (microCi/g) concentrations fit second order polynomials (r2 = 0.995-0.999). The results show that [14C]plastic standards are valid for measuring [125I] radioactivity in tissue slices by autoradiography with HFBM.