Insulin receptors and insulin action in dissociated brain cells

The present study was conducted to characterize insulin receptors and insulin action in rat brain cells. Binding of [¹²⁵I]insulin to cells obtained by mechanicaly dissociating rat brains was 86% specific, time-dependent and reached equilibrium within 90 min. The t _{1 2} of association was 14 min and t _{1 2} of dissociation was 8 min. Scatchard analysis demonstrated the typical curvilinear plot providing high affinity (0.03 nM) and low affinity (6.6 nM) binding sites. The total number of binding sites were 0.15 pmol/mg protein. Crosslinking of [¹²⁵I]insulin to its receptors on dissociated brain cells followed by SDS-PAGE and autoradiography showed that the α-subunit of the receptor had a molecular weight of 122,000. This was in contrast with a molecular weight of 134,000 for the liver α-subunit. Incubation of dissociated brain cells with insulin resulted in a concentration-dependent inhibition of total [³H]norepinephrine (NE) uptake. This inhibitory effect of insulin on [³H]NE uptake was soduim ino-dependent suggesting that 80-98% of the sodium ion-dependent uptake was insulin-sensitive. Incubation of lectin-purified insulin receptors with insulin resulted in a time- and concentration-dependent stimulation of phosphorylation of the tyrosine residue of an exogenous substrate poly (GLU, Tyr) (4:1). In addition, insulin also stimulated the autophosphorylation of the β-subunit of the insulin receptors. These observations corroborate our contentio that insulin exerts neuromodulation effects mediated by the specific insulin receptors in the brain.