Figure 5

Couplet cells with Trefones IGF-I and IGFBP-n and their membrane receptors. One Trefone added to one cell type stimulates the production of the couplet Trefone. IGF-I from the a-Cell will stimulate the production of an IGFBP by the i-Cell, and conversely. This is similar to FIGURE3(b). (In another couplet of cells, IGF-II would bind its own specific IGFBP-n).