Pharmacology and biophysical properties of alpha 7 and alpha 7-alpha 8 alpha-bungarotoxin receptor subtypes immunopurified from the chick optic lobe.
Two chick optic lobe alpha-bungarotoxin receptor subtypes (alpha 7 and alpha 7-alpha 8) were immunopurified using polyclonal antibodies raised against synthetic peptides of chick alpha 7 and alpha 8 alpha-bungarotoxin receptor subunits. The alpha 7 subtype contained the M(r) 57,000 alpha 7 subunit, and represented 60-70% of the alpha-bungarotoxin receptors; the alpha 7-alpha 8 subtype contained the M(r) 57,000 alpha 7 and alpha 8 subunits, and represented only 20-25% of the receptors. Both subtypes also had an additional M(r) 52,000 subunit. The affinity of these subtypes for alpha-bungarotoxin as well as antagonists was similar. However, the alpha 7-alpha 8 subtype displayed consistently higher affinities for agonists. When reconstituted in planar lipid bilayers, the alpha 7-alpha 8 subtype displayed several conductance states of 10-50 pS; the alpha 7 subtype had only one conductance state of 45 pS. The alpha 7-alpha 8 subtype was activated by lower agonist concentrations than the alpha 7 subtype. When expressed in Xenopus oocytes, the alpha 8 subunit formed functional homomeric receptors that desensitized rapidly. These channels were blocked by alpha-bungarotoxin and displayed a higher affinity for agonists than the alpha 7 homomeric receptor. Taken together, these data indicate that at least two alpha-bungarotoxin subtypes are present in the chick optic lobe. They operate as ligand-gated channels and display different agonist sensitivities and kinetics/conductance properties.
Gotti
C
C
Department of Medical Pharmacology, University of Milan, Italy.
Hanke
W
W
Maury
K
K
Moretti
M
M
Ballivet
M
M
Clementi
F
F
Bertrand
D
D
D000818:Animals; D015153:Blotting, Western; D001923:Brain Chemistry / Q000187:drug effects / Q000502:physiology*; D002038:Bungarotoxins / Q000737:chemistry*; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D002645:Chickens; D002846:Chromatography, Affinity; D004591:Electrophoresis, Polyacrylamide Gel; D004594:Electrophysiology; D007120:Immunochemistry; D015640:Ion Channel Gating / Q000187:drug effects; D008051:Lipid Bilayers; D011233:Precipitin Tests; D011950:Receptors, Cholinergic / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000737:chemistry / Q000187:drug effects*; D014981:Xenopus; D064569:alpha7 Nicotinic Acetylcholine Receptor
D002038:Bungarotoxins; D008051:Lipid Bilayers; D011950:Receptors, Cholinergic; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; D002217:Carbachol; D002118:Calcium