IMPROVED METHOD FOR AUTORADIOGRAPHIC LOCALIZATION OF BETA-ADRENOCEPTORS USING PHOTOAFFINITY-LABELING

Contact autoradiography of tissue sections, using emulsion coated cove rslips or X-ray films, is widely used to provide information about the regional distribution of receptors. This easy to perform, standard te chnique has the disadvantage of an image spread due to the gap between the radioactive source and the film. The present study describes a ne w technique which combines photoaffinity labeling of beta-adrenoceptor s with ''dipping'' autoradiography and a modified trichrome stain. Inc ubation of 16 mum cryosections of rat lung tissue with the iodinated, photoaffintiy labeling, non-selective, beta-adrenergic agonist [I-125] -cyanopindololazide II ([I-125]-CYPA II) (100 pmol/1) in the absence o r presence of 1 mumol (+/-)-propranolol revealed strong, specific 8-ad renoceptor binding to alveolar parenchyma and bronchial epithelium of large and small bronchioles, lesser binding to smooth muscle bundles o f large airways and only sparse binding to the smooth muscle of small bronchioles or peripheral branches of pulmonary artery. With standard autoradiographic techniques, a similiar distribution of the label was obtained, although resolution and sensitivity were inferior. Staining of tissue sections through the photoemulison by means of a modified Ma llory's trichrome dye facilitated the discrimination between alveolar and bronchial epithelium, muscular and collagenous tissues. In conclus ion, the photoaffinity labeling of 8-adrenoceptors with [I-125]-CYPA I I allows the use of ''dipping'' autoradiography. This technique, in co mbination with trichrome staining through the photoemulsion, results i n an improved autoradiograpic image together with a better association of the label with distinct histological structures and the higher sen sitivity of the method.