Identification of lymphoid cell lines bearing receptors for somatostatin.

The MT-2, derived from an adult T-cell leukaemia (ATL) cell, the Molt-4F, a human T-cell line, and the Isk, an EB virus-transformed B-cell line, were found to have high-affinity receptors for somatostatin, a cyclic tetradecapeptide that inhibits the release of substances such as growth hormone, TSH, glucagon, insulin, secretin, gastrin and cholecystokinin. The quantity of radioactivity bound varied linearly with the number of cells, and was displaced by non-radioactive somatostatin in a concentration-dependent manner. Specific binding of 125I-somatostatin was time- and temperature-dependent and at 22 degrees reached equilibrium within 120 min. Scatchard analysis demonstrated one class of specific-binding sites on MT-2 cells, Isk cells and Molt-4F cells that had respective densities and dissociation constants of 109 pM and 0.64 nM, 102 pM and 1.1 nM, and 5.8 pM and 0.22 nM.