Beta-adrenergic receptors in catfish liver membranes: characterization and coupling to adenylate cyclase.
beta-Adrenergic binding sites in catfish liver membranes have been characterized by centrifugal assay, using a beta-adrenergic receptor antagonist, (-)-[3H]dihydroalprenolol ([3H]DHA). Binding of the radioligand was saturable and reversible. At 22 degrees equilibrium conditions were established in 15 min and the half-time for dissociation of bound [3H]DHA was approximately 4 min. Analysis of binding data was compatible with the existence of two classes of binding sites: a low-affinity site had a Kd of 62.3 nM and a Bmax of 452.0 fmol/mg protein, while the high-affinity site had a Kd of 2.04 nM and a Bmax of 46.7 fmol/mg protein. The dissociation constant of (-)-alprenolol for the beta-adrenergic receptors was about 2 nM as determined independently by direct kinetic studies and by inhibition of isoproterenol-stimulated adenylate cyclase activity. Phenylephrine was as potent as other catecholamines in inhibiting [3H]DHA binding, indicating that fish adrenoceptor subtyping is different from that of mammals.
Fabbri
E
E
Institute of General Physiology, University of Ferrara, Italy.
Brighenti
L
L
Ottolenghi
C
C
Puviani
A C
AC
Capuzzo
A
A
D015720:5'-Nucleotidase / Q000378:metabolism; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D007059:Ictaluridae / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008566:Membranes / Q000378:metabolism; D011869:Radioligand Assay; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*
D011943:Receptors, Adrenergic, beta; D015720:5'-Nucleotidase; D000262:Adenylyl Cyclases