Insulin inhibition of calcium binding by human placental membrane

Insulin and its analogues displaced membrane-bound calcium within a physiological range of insulin concentration, in proportion to both biological potency and ability to displace porcine 125 I-labelled insulin from the insulin receptor. Mild tryptic digestion of the membrane reduced insulin binding but did not reduce specific calcium binding. Displacement of membrane-bound calcium by insulin was dependent on insulin binding to its intact receptor. These studies suggest that Ca2"ay exert a controlling influence on insulin-receptor binding in vivo.