The Influence of Tracers on Insulin Binding to Human Erythrocytes

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Abstract
Insulin binding to human erythrocytes using 2 different 125I-insulin-tracers was studied. Erythrocytes of 8 normal subjects were examined using [mono-125I-(Tyr A 14)]insulin as tracer. Three of these erythrocyte preparations were examined simultaneously using [125I]insulin, which was randomly iodinated by the chloroamine-T-method. Data were analyzed by a computerized non-linear least-squares procedure both on the basis of 1 and 2 class receptor models. Only the 1 class receptor model yielded consistent results. When the 2 class receptor model was applied the low affinity branch of the Scatchard plot was not reproducible. On the basis of the 1 class receptor model the number of receptor sites was lower (Ro = 0.046 .+-. 0.006 nmol/l equivalent to 6.3 .+-. 0.8 receptors/erythrocyte) with [mono-125-I-(Tyr A 14)]insulin as compared to [125I]insulin randomly iodinated by the chloramine-T method (R0 = 0.070 .+-. 0.008 nmol/l equivalent to 9.6 .+-. 1.1 receptors/erythrocyte). Conversely, the affinity of the [mono-125I-(Tyr A 14)]insulin was higher (Ka = 2.6 .+-. 0.3 .times. 109 l .cntdot. mol-l vs. 1.9 .+-. 0.2 .times. 109 l .cntdot. mol-l).

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