Identification and characterisation of beta-adrenoceptors in guinea-pig skeletal muscle.

(-)-[125I]Iodocyanopindolol (ICYP) was used to characterise beta-adrenoceptors in skeletal muscle of the guinea-pig. The binding if ICYP to soleus and gastrocnemius muscles was saturable and reversible with KD values of 10.7 +/- 1.1 and 11.6 +/- 1.4 pM and Bmax values of 84.0 +/- 5.7 and 59.9 +/- 8.6 fmol/mg protein for gastrocnemius and soleus muscles respectively. Hofstee plots for the selective beta 1-adrenoceptor antagonists atenolol and metoprolol and for the selective beta 2-adrenoceptor antagonist ICI 118551 were linear in both skeletal muscles suggesting the presence of homogenous populations of beta-adrenoceptors. Furthermore, from the Ki values for atenolol (8381 +/- 2063 nM), metoprolol (585 +/- 80 nM) and ICI 118551 (0.39 +/- 0.05 nM) in gastrocnemius and ICI 118551 (0.47 +/- 0.09 nM) in soleus muscle, it is concluded that the beta-adrenoceptors in skeletal muscle of the guinea-pig are predominantly if not exclusively of the beta 2-subtype.