QUANTITATIVE CHARACTERIZATION OF BETA-ADRENERGIC-RECEPTOR SUBTYPES IN PORCINE ADIPOCYTES

1. Two populations of beta-adrenergic receptor (beta-AR) subtypes and their proportions were characterized in adipocytes isolated from subcutaneous adipose tissue of castrated male crossbred pigs (60-85 kg). 2. Specific binding of the radioligand I-125-iodopindolol (IPIN) to crude plasma membranes (70-90% of total binding) reached equilibrium conditions in 30 min (38-degrees-C), was tissue concentration-dependent, stereospecific and saturable (b(max) = 168 +/- 5.8 fmol/mg protein). 3. Displacement curves by ICI 89,406 were best-fit by a two site model (P < 0.01) that indicated the presence of two receptor populations and selectivity of IPIN for the beta-2AR subtype. 4. Forty-five percent of the receptors had a high affinity for ICI 89,406, K(i) = 2.27 +/- 0.68 nM and were classified as beta-1AR.