Glucagon Receptor of Rat Renal Tubular Cells

Abstract

The interaction of glucagon and rat renal tubular cells isolated by collagenase digestion and nylon mesh filtration was studied. The results obtained were as follows.
(1) ¹²⁵I-Glucagon binding study
Tubule-rich fraction (TRF) and ¹²⁵I-glucagon were incubated with or without a large excess of native glucagon (10μg/ml) in the presence of 500μM bacitracin at 4°C The specific ¹²⁵I-glucagon binding rate reached a plateau at 30-60 min and showed an almost linear correlation with the TRF protein concentration (up to 2.3 mg). A displacement study carried out by the addition of various concentrations of native glucagon to the above assay system resulted in a dose-dependent inhibition of binding, and the native glucagon concentration to obtain 50% binding inhibition was about 27 ng/ml. Scatchard plots of the above data yielded a curvilinear form, which suggested the presence of two kinds of receptor sites of different affinity or negative cooperativity. The high affinity site had a binding capacity of about 0.375 ng/1 mg TRF protein and an affinity constant of about 0.17×10⁹ M^-1.
(2) Cyclic AMP response to native glucagon
The cyclic AMP production of TRF incubated at 25°C increased in the presence of glucagon (6.25 μ/ml), and was correlated linearly with the incubation time (up to 10 min) and TRF protein concentration (up to 2 mg). The cyclic AMP response to various concentrations of glucagon was dose-dependent, and the concentration of glucagon to obtain half-maximum stimulation was about 12.5 ng/ml.
All the above results suggest that renal tubular cells have glucagon receptors and a glucagonsensitive adenyl cyclase system.