A study of insulin receptors in human mononuclear leucocytes.

Insulin binding sites were demonstrated in human mononuclear leucocytes by use of a technique which includes isolation of mononuclear leucocytes from defibrinated blood and separation of cell bound and free [125I]insulin with silicone oil. The binding was time and temperature dependent. At 15 degrees C equilibrium was reached after 90 min and a plateau maintained for at least 50 min. Incubations were carried out at 4 degrees C, 15 degrees C and 37 degrees C. Maximal binding was obtained at 15 degrees C. The optimum pH for insulin receptor interaction occurred at about 8. [125I]insulin binding to mononuclear leucocytes was demonstrated to be a linear function of cell number concentration over a range of 17-70 X 10(6) X ml-1. The binding was a displaceable function of native insulin concentration. In a group of 21 young healthy persons with normal body weight we found a mean specific cell binding fraction of 1.92 +/- 0.58 (s) X 10(-2). Analysis of the equilibrium between insulin and its receptor revealed an apparent heterogeneity of insulin receptors.