Figure 4.

Glucagon receptor function in plasma membranes isolated from normal human and patient liver (A and B) and in COS-7 cells expressing the wild-type or mutant glucagon receptor (C and D). (A) Binding of ¹²⁵I-labeled glucagon with (non-specific binding) and without (B0: total binding) addition of 1 µM unlabeled glucagon after incubation with aliquots of membranes containing 50 µg protein for 90 min. Shown are means and standard deviations of three determinations. (B) Accumulation of cAMP after incubation for 90 min with 1 µM glucagon, forskolin or epinephrine. The values presented are means and standard deviations of four determinations. (C) Competition binding of ¹²⁵I-glucagon with (NSB) and without (B0) the addition of 1 µM unlabeled glucagon and (D) accumulation of cAMP using COS-7 cells expressing the cloned wild-type human glucagon receptor (wt-GR) or the mutant receptors in which the 70 base pairs encoded by exon 9 have been deleted (Δ70-GR).