Homogeneous class of beta-1 adrenergic receptors in rat kidney identification by (±)- 125iodocyanopindolol binding

Abstract

The highly specific β-adrenergic radio-ligand (±)- 125iodocyanopindolol (ICYP) was used to characterize the β-adrenergic receptor subtype present in rat kidney. Binding of ICYP to membranes from rat kidney was of high affinity ( K D = 69.9 pM) and saturable with 1.06 pmoles ICYP bound/g tissue wet wt at maximal occupancy of the sites. Analysis of inhibition of ICYP binding by β 1- and β 2-selective adrenergic drugs via pseudo-Scatchard (‘Hofstee’) plots resulted in linear plots indicating the existence of a homogeneous population of β-adrenergic receptors. From the resulting K D-values for practolol (2.2 μM), metoprolol (0.21 μM), zinterol (0.4 μM) and IPS 339 (0·046 μM) it is concluded that the β-adrenergic receptor in rat kidney is of the β 1-subtype. This subclassification is further supported by the fact that (−)-noradrenaline and (−)-adrenaline were equipotent in inhibiting ICYP binding. The β-adrenergic agonists (−)-isoprenaline and zinterol bind to two distinct states of this β 1-receptor, a high and low affinity state. GTP (10 −4 M) converts this heterogeneous binding into a homogeneous low affinity binding.