Binding of tyrosine-A-14(125I)-monoiodoinsulin to human erythrocytes

Insulin degradation by intact erythrocytes is associated with low-affinity insulin binding sites

The effect of Con A and glucose on insulin binding and receptor-mediated degradation by intact erythrocytes was studied. Con A blocked totally high-affinity insulin binding but did not change low-affinity binding. Glucose at the concentration of 25 mM produced a bidirectional effect; it increased high-affinity insulin binding but decreased low-affinity binding. Con A did not affect receptor-mediated insulin degradation rate. Glucose caused a clear decrement in insulin degradation rate. These results show that insulin degradation by intact erythrocytes is closely associated with the low-affinity insulin receptor. The two-site model for the insulin receptor is favored by the present findings.

Effect of surgical stress on the erythrocyte insulin receptor

The aim of this study was to investigate whether surgical trauma causes changes in insulin receptors which may have significance on the causation of post-traumatic insulin resistance. Twenty-four patients scheduled for lumbar intervertebral disc operations or thoracotomy were investigated. In patients who did not receive glucose during operation blood glucose and plasma insulin concentrations did not change but lipolysis was induced as indicated by the increase of serum free fatty acids concentration. Glucose infusion (5% w/v) caused a hyperglycaemic and hyperinsulaenemic response without lipolysis. In patients not receiving a glucose load the number of insulin receptors on erythrocyte measured 4 h postoperatively increased from the preoperative values and the affinity of the receptors to insulin in physiological concentration range increased. In patients with glucose load the number of receptors decreased and receptor affinity to insulin at physiological concentration decreased. The results suggest that in patients receiving a glucose load the receptor changes indicate the perioperative development of insulin resistance at receptor level.

Quality control of insulin radioreceptor assay for human erythrocytes. Effect of ageing of mono-125I-Tyr-A14-insulin preparation

The quality control of insulin radioreceptor assay for human erythrocytes is based on the storage of erythrocyte preparations in Hepes buffer of pH 8.0, containing 10 g/l of albumin and 20 mmol/l of glucose. The change of erythrocytes into spherocytes and crenated cells reduces the apparent number of insulin receptors in a relatively constant way by less than 8% a week after 10 days of storage. At the same time the dissociation constants of the insulin-receptor complex increase rapidly. Thus the use of a preparation must be limited to controlling the determination of the insulin binding sites of erythrocytes, and not to the measurement of the affinities of the receptors. When mono-125I-Tyr-A14-insulin gets old, a slow decrease in the insulin binding sites can be measured, but the dissociation constants of the insulin receptor complex are not affected.