Identification and characterization of alpha 1- and beta 2-adrenergic receptors in human liver.
Adrenergic receptors were identified in healthy human hepatic tissue from thirty-nine subjects undergoing elective abdominal surgery by using the specific alpha 1-antagonist [3H]-prazosin and the beta adrenergic antagonist [3H]-dihydroalprenolol ([3H]-DHA). [3H]-prazosin binding to plasma membranes was rapid, of high affinity, saturable and stereospecific with a maximal binding capacity (Bmax) of 74.1 +/- 5.5 fmol mg-1 of protein. The displacement curve for (-)-norepinephrine was better explained by a one-site binding and after addition of GTP 0.1 mM the curve was not right-shifted, suggesting the majority of alpha receptors in healthy human liver are of the alpha 1 subtype and not linked to a GTP-binding protein. [3H]-DHA binding to liver plasma membranes was also rapid, of high affinity, saturable and stereospecific with a Bmax 96.5 +/- 10.3 fmol mg-1 of protein of receptors. Computer aided analysis of the displacement curve of ICI 118,551, a subtype selective beta 2-antagonist (IC50 = 62 +/- 2 nM), indicated a one-site binding, thus, showing that beta adrenergic receptors are of the beta 2 subtype. The displacement curve of [3H]-DHA for (-)-isoproterenol was right shifted by GTP indicating that beta 2 adrenergic receptors are linked to a GTP-binding protein in human liver. These results indicate that alpha 1- and beta 2-receptors co-exist in human liver but only beta 2-receptors are linked to a GTP-binding protein.
Bevilacqua
M
M
Servizio di Endocrinologia Ospedale L. Sacco Vialba, Milano, Italy.
Vago
T
T
Norbiato
G
G
Chebat
E
E
Baldi
G
G
Meroni
R
R
Regalia
E
E
D002462:Cell Membrane / Q000378:metabolism; D004082:Dihydroalprenolol / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D011224:Prazosin / Q000378:metabolism; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*
D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D004082:Dihydroalprenolol; D011224:Prazosin