Figure 3
Couplet Trefones and cells and their membrane receptors. (a) A couplet of cells ( a C and i C) with each producing a soluble Trefone and each having a receptor (R) to bind the soluble Trefone produced by the other cell. a R on i C binds a T and i R on a C binds i T. (b) A couplet of cells with the a-Cell producing the “a” Trefone, IGF-I, the i-Cell producing the “i” Trefone, one specific IGFBP, and each having a receptor to bind the Trefone produced by the other cell. There is a receptor for IGF-I on the i-Cell and a receptor for the IGFBPn on the a-Cell.