An inexpensive microcomputer digital imaging system for densitometry: quantitative autoradiography of insulin receptors with 125I and LKB Ultrofilm.

This article describes a video digitizing system designed for measuring film optical density. The system, which is based on a 6-bit (64 gray level) digitizer, solid state video camera, and Apple II microcomputer, digitizes a rectangular area selected by the operator and converts the gray level values into preselected standard units. In order to develop autoradiographic standard curves for quantitative autoradiography with 125I-insulin, liver slices labeled with 125I-insulin and plastic sections containing known amounts of tritium were apposed to the same sheet of LKB Ultrofilm for exposures of 1-7 days. The results indicate that 3H plastic standards can be used to calibrate QAR of 125I-labeled ligands with LKB Ultrofilm. The Apple system was also used to measure binding of 125I-insulin to the external plexiform layer (EPL) in slices of the rat olfactory bulb. Results suggest that the EPL has two binding sites for insulin, a high affinity site with Kd = 1.0 X 10(-8) M and a low affinity site having a Kd = 1.4 X 10(-5) M.