Quantitative electron microscopic autoradiography of insulin, glucagon, and somatostatin binding sites on islets

After monolayer cultures of rat islets were exposed to [(125)I]insulin,[(125)I]glucagon, and [(125)I]tyrosinyl somatostatin, specific autoradiographic grains associated with each radioactively labeled ligand were found on B, A, and D cells. The density of labeling of the B, A, and D cells with each labeled ligand correlated well with the known actions of the three hormones on each of the islet cells.