Beta-Adrenergic receptor subtypes in myocytes, arteries, and arterioles of the porcine heart identified with autoradiographic procedures

Beta (P) adrenergic receptors are localized in several tissue compartments of the heart, but it has been unclear as to the relative numbers contained in each compartment. The goal of the current study was to use receptor autoradiography to analyze p receptor agonist binding characteristics in different tissue compartments of pig heart including cardiac myocytes (predominately P1), coronary arteries (predominately P1) and coronary arterioles (predominately ~2). In addition, the relative numbers of ~1- and 132-adrenergic receptors in these tissue compartments were estimated. Blocks of porcine anterior interventricular sulcus were frozen and tissue sections cut. Sections were incubated in [1251]-(-) iodopindolol {1251-IPIN) in the presence of 10·5 M of the P agonist, DL-propanolol HCI, or 5 x 10·1 M of the ~1 selective antagonist, CGP 20712A. For the validation experiments radioactivity was determined in the gamma counter and the sections demonstrated rapid binding, saturability and stereoselectivity. For autoradiography, emulsion-coated coverslips were attached to the slides. After exposure, the slides were developed and stained, and grain density quantified. There was a greater density of 13-adrenergic receptors, identified by autoradiographic grains, over arterioles as compared to the left anterior descending (LAD) artery. The LAD artery had only one-sixth the density of 13-adrenergic receptors seen in the arterioles, while the myocytes were equivalent to the arterioles.