The Possible Role of c-AMP in the Irradiation Induced Contraction of Nerve Muscle Preparation

Abstract

c-AMP acts as a key-substance in transforming the stimulation by transmittors via cell receptors into mechanical and electrical cell activities. ß-adrenergic receptors activate the adenylate cyclase, leading to an increase of the c-PMP concentration and to a relaxation of the nerve-muscle preparation. By addition of dibutyryl-c-AMP to preparations of frog lung and rat aorta the radiation induced contraction could be reversed. This ability of c-AMP is lost by X-irradiation in vitro, probably due to changes of the molecular structure. The physiological activity decreases far more than it would be expected from measurements of the absorbance at 260 nm which is attributed to the intact purine ring. Thin-layer chromatograms show substances of lower R_f-values, produced during radiolysis by addition of OH radicals and H-atoms. Reflexionspectra and difference spectra (irradiated minus unirradiated c-PMP) point into the same direction. The effect of the radiation products is compared with the effect of a shift in the c-AMP/AMP equilibrium within the cell. Experiments with frog lung preparations showed4hat the addition of 10 % AMP to Dib-c-PMP (total concentration 10^-4M) converted the relaxation of approximately 30% into a contraction of ca 11 %.