The muscle slice--a new preparation for the characterization of beta-adrenergic binding in fast- and slow-twitch skeletal muscle

Abstract

A new procedure is presented that characterizes the specific binding of the beta-adrenergic antagonist, [3H]CGP-12177, to thick (1 mm) slices from fast-twitch [extensor digitorum longus (EDL)] and slow-twitch (soleus) mouse skeletal muscle. Binding is reversible, saturable, stereospecific, of high affinity, and subject to agonist-induced desensitization, indicating that it is to beta-adrenoreceptors and not to other sites. In both muscles, the majority of specific binding is to the beta 2-receptor subtype. Bmax is approximately twice as high in the soleus (5.64 +/- 0.52 fmol/mg wet weight) as in the EDL (2.66 +/- 0.29 fmol/mg wet weight) (P less than 0.05), whereas affinity is higher in the fast-twitch (Kd = 0.30 +/- 0.08 nM) than the slow-twitch muscle (Kd = 0.45 +/- 0.08 nM). The minimal tissue disruption associated with this procedure, as well as its speed, simplicity and relatively low cost, suggest that the slice preparation may prove to be invaluable for the future study of beta-adrenergic receptor binding and associated responses in skeletal muscle.