Regulation of calcitonin secretion in vitro

We have developed methods for the long-term maintenance of monolayer cultures of both human and trout calcitonin-secreting (C-) cells (Roos et al., 1974a, 1975). Secreted calcitonin (CT) can be measured by specific and sensitive radioimmunoassays for human calcitonin (HCT) and trout calcitonin (TCT) (Deftos, 1971; Deftos et al., 1974; Roos et al., 1974b). The combined application of these cell culture and radioimmunoassay methods to the in vitro study of CT secretion has revealed fundamental differences in the regulation by divalent ions of CT secretion in mammalian and nonmammalian C-cells. Our results also indicate a specific role for secretin as a CT secretagogue in trout. In addition to establishing the individual secretory effects of calcium and the enteric polypeptide hormones on the C-cells of both species, we have investigated the combined effects of these agents in both human and trout C-cell cultures. The noncompetitive augmentation of the secretory effects resulting from the actions of specific combinations of these secretagogues in each of these C-cell populations suggests that CT secretion is regulated by co-ordinate interaction of specific ionic and peptide secretagogues. An elucidation of the cellular mechanisms involved in such multifactorial control of C-cell function should result from the continued investigation of CT secretion in these C-cell cultures.