Pharmacological characterization of alpha-bungarotoxin-sensitive acetylcholine receptors immunoisolated from chick retina: contrasting properties of alpha 7 and alpha 8 subunit-containing subtypes.
At least three subtypes of alpha-bungarotoxin-sensitive acetylcholine receptors (alpha Bgt-sensitive AChRs) exist in chick brain and retina. All may contain previously unknown structural subunits. One subtype contains alpha 7 subunits. Another contains alpha 8 subunits. A third contains both alpha 7 and alpha 8 subunits. In this article, we describe, for the first time, the pharmacological characterization of alpha 7 AChRs and alpha 8 AChRs immunoisolated from chick retina. Pharmacologically, the alpha 8 AChRs exhibit two classes of binding sites, the high affinity of which have higher affinity for most cholinergic ligands than do alpha 7 AChRs. These differences are most accentuated for ACh (approximately 5400-fold), decamethonium (approximately 1400-fold), 1,1,-dimethyl-4 phenylpiperazinium (approximately 200-fold), atropine (approximately 200-fold), nicotine (approximately 100-fold), and tetramethylammonium (approximately 100-fold). The alpha 8 AChR low affinity sites exhibit affinities that are similar but not identical to that of alpha 7 AChRs. Many of the pharmacological differences between the alpha 7 AChRs and alpha 8 AChRs can be attributed to the limited differences between the amino acid sequences of the N-terminal region of the alpha 7 and alpha 8 subunits because expressed alpha 7 homomers and alpha 8 homomers also exhibit these characteristic differences.
Anand
R
R
Department of Neuroscience, University of Pennsylvania, Philadelphia 19104-6074.
Peng
X
X
Ballesta
J J
JJ
Lindstrom
J
J
D000818:Animals; D001665:Binding Sites; D002038:Bungarotoxins / Q000494:pharmacology*; D002642:Chick Embryo; D002846:Chromatography, Affinity; D007120:Immunochemistry; D011950:Receptors, Cholinergic / Q000145:classification / Q000187:drug effects* / Q000302:isolation & purification / Q000378:metabolism; D012160:Retina / Q000378:metabolism*
D002038:Bungarotoxins; D011950:Receptors, Cholinergic