β‐Adrenoceptors of the human myocardium: determination of β₁ and β₂ subtypes by radioligand binding

beta-Adrenoceptors of the human myocardium were investigated with binding studies using 125iodocyanopindolol (ICYP) as ligand. Inhibition of ICYP-binding by betaxolol (a selective beta 1-antagonist) and ICI 118551 (a selective beta 2-blocking drug) resulted in non-linear Scatchard-plots suggesting that both beta-adrenoceptor subtypes are present in human left atrium and left ventricle. Computer analysis of the data gave a beta 1/beta 2-adrenoceptor ratio of approximately 65:35 both for left atrium and for left ventricle.