Characterization of the Glucagon Receptor in a Pheochromocytoma

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Abstract
Glucagon activated adenylate cyclase in a homogenate of a pheochromocytoma over the concentration range 1 × 10‒8M to 1 × 10‒6M. Several other hormones including adrenocorticotropin, thyrotropin, parathyroid hormone and histamine were without effect. The tumor glucagon receptor was characterized and found to be similar in several ways to the glucagon receptor previously reported in normal tissue such as liver and heart. One, the receptor specifically bound l25I-glucagon. Two, solubilization of the pheochromocytoma abolished glucagon-activation of the adenylate cyclase. Three, glucagon-responsiveness of the adenylate cyclase was partially restored, by the addition of phosphatidylserine to the incubations. One major difference was observed between the glucagon receptor in tumor tissue and that in liver and heart, namely, a marked lability in 125I-glueagon binding and adenylate cyclase activity. Within four days, despite storage in liquid nitrogen, 75% of the binding activity and all of the adenylate cyclase activity in the solubilized preparation were lost. The factor(s) responsible for this lability remains unidenified.

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