Insulin receptors in isolated adult mouse intestinal cells: studies in vivo and in organ culture.

Isolated intestinal cells from adult mice possess a high concentration of insulin receptors. The binding capacity and the number of binding sites are higher in duodenum than in jejunum or ileum and in the upper part of the villus than in the crypts. The specific binding is, respectively, 11.8 +/- 1.0%, 9.1 +/- 4.0%, and 5.5 +/- 0.3%/mg . protein for duodenum, jejunum, and ileum. The number of high affinity sites per cell is, respectively, 11.0 X 10(3), 3 X 10(3), and 2.5 X 10(3). The number of low affinity sites per cell is, respectively, 11.0 X 10(4), 4.1 X 10(3), and 3.9 X 10(3). This specific binding increases to 15.9 +/- 0.9% after 24 h of fasting and to 24.5 +/- 2.2% mg protein after 48 h of fasting. This increase is due not only to an increment in the number of sites but also to alterations in affinity constants (K1, control, 0.380, 48-h fasting, 0.044 X 10(9) M-1; K2, control, 1.20, 48-h fasting; 2.61 X 10(7) M-1). The receptors are mainly located on the basolateral and internal membranes (P1, 9.4 +/- 0.7%/mg protein), but are also present on brush border membranes (P2, 2.6 +/- 1.1%/mg protein, P less than 0.01). After 24 h of organ culture, the specific binding is not modified in duodenal explants. Moreover, in the presence of insulin in the culture medium, the binding is decreased by 59%.