Endocrinology, Vol 121, 1784-1788, Copyright © 1987 by Endocrine Society

ARTICLES

Evidence for the presence of type I insulin-like growth factor receptors on rat pancreatic A and B cells

CF Van Schravendijk, A Foriers, JL Van den Brande and DG Pipeleers
Department of Metabolism and Endocrinology, Vrije Universiteit Brussel, Belgium.

Purified rat pancreatic islet cells express somatomedin receptors which are identified by their affinity for insulin-like growth factor (IGF)- I, IGF-II, and insulin. Binding of [125I]IGF-I to islet A cells was half-maximally inhibited by 7.10(-10) M IGF-I, while IGF-II, insulin, and proinsulin were respectively 10-, 500-, and 10,000-fold less potent displacers of IGF-I binding. Unrelated hormones such as glucagon or GH did not compete with [125I]IGF-I binding to A cells. The concentration of IGF-I receptors on A cells was estimated at 5000 IGF-I binding sites per cell with affinity constant (Ka) of 2 X 10(9) M-1. Islet B cells were found to exhibit a reversible time- and temperature-dependent binding with [125I]IGF-I. Specificity and affinity of IGF-I binding sites were identical for islet A and B cells. Linear Scatchard plots of competitive binding data on B cells suggest 1 single class of IGF-I receptors in a concentration of 12,000 sites per cell. The presence of high affinity receptors for IGF-I on adult islet A and B cells provides a molecular basis for this growth factor to influence growth, survival, and/or function of these endocrine cell types. Their low affinity for insulin should be considered as a potential mechanism for this hormone to influence, at high concentration, the function of islet A and B cells.

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