Binding of adrenergic ligands to liver plasma membrane preparations from the axolotl, Ambystoma mexicanum; the toad, Xenopus laevis; and the Australian lungfish, Neoceratodus forsteri.
The beta-adrenergic ligand iodocyanopindolol (ICP) bound specifically to hepatic plasma membrane preparations from the axolotl, Ambystoma mexicanum (Bmax, 40 fmol/mg protein (P) at free concentration above 140 pM; KD, 42 pM); the toad, Xenopus laevis (Bmax, 200 fmol/mg P at 1 nM; KD, 300 pM); and the Australian lungfish, Neoceratodus forsteri (Bmax, 100 fmol/mg P at 5 nM). For the lungfish, the Scatchard plot was curved showing two classes of binding site with KD's of 20 and 500 pM. Neither the alpha 1-adrenergic ligand prazosin nor the alpha 2-adrenergic ligand yohimbine bound specifically to hepatic membrane preparations from any of the three species. Several adrenergic ligands displaced ICP from hepatic membrane preparations of all three species with KD's of Axolotl--propranolol, 50 nM; isoprenaline, 600 nM; adrenaline, 10 microM; phenylephrine, 20 microM; noradrenaline, 40 microM; and phentolamine, greater than 100 microM; X. laevis--propranolol, 30 nM; isoprenaline, 100 microM; adrenaline, 200 microM; noradrenaline, 300 microM; phenylephrine, 1 mM; and phentolamine, greater than 1 mM; N. forsteri,--propranolol, 25 nM; isoprenaline, 1 microM; adrenaline, 20 microM; phenylephrine, 35 microM; noradrenaline, 600 microM; and phentolamine, 400 microM. These findings suggest that alpha-adrenergic receptors are not present in hepatic plasma membrane preparations from these three species and that the hepatic actions of catecholamines are mediated via beta-adrenergic receptors. The order of binding of the beta-adrenergic ligands suggests that the receptors are of the beta 2 type.
Janssens
P A
PA
Department of Zoology, Australian National University, Canberra.
Grigg
J A
JA
D000557:Ambystoma / Q000378:metabolism*; D000558:Ambystoma mexicanum / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D005399:Fishes / Q000378:metabolism*; D020120:Iodocyanopindolol; D008024:Ligands / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D010869:Pindolol / Q000031:analogs & derivatives / Q000378:metabolism; D011224:Prazosin / Q000378:metabolism; D011869:Radioligand Assay; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism* / Q000502:physiology; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D014982:Xenopus laevis / Q000378:metabolism*
D008024:Ligands; D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D020120:Iodocyanopindolol; D010869:Pindolol; D011224:Prazosin