Inhibition of insulin receptor binding by A23187: synergy with phorbol esters

The ionophore A23187 inhibits the binding of insulin on U-937 monocyte-like cells which had been induced to differentiate by 1 alpha, 25-(OH)2 cholecalciferol, while it remains inactive on the undifferentiated cells. A 50% reduction of the specific binding of 125I-insulin is observed within 20 to 30 min at 37 degrees C. The effect is obtained at 10(-7)M to 10(-6)M A23187. It is reversible in 60 min at 37 degrees C. A suboptimal concentration of the ionophore potentiates the inhibitory action of phorbol esters on insulin binding.