PHARMACOLOGICAL CHARACTERIZATION OF ALPHA-BUNGAROTOXIN-SENSITIVE ACETYLCHOLINE-RECEPTORS IMMUNOISOLATED FROM CHICK RETINA - CONTRASTING PROPERTIES OF ALPHA-7-SUBUNIT-CONTAINING AND ALPHA-8-SUBUNIT-CONTAINING SUBTYPES
R. Anand et al., PHARMACOLOGICAL CHARACTERIZATION OF ALPHA-BUNGAROTOXIN-SENSITIVE ACETYLCHOLINE-RECEPTORS IMMUNOISOLATED FROM CHICK RETINA - CONTRASTING PROPERTIES OF ALPHA-7-SUBUNIT-CONTAINING AND ALPHA-8-SUBUNIT-CONTAINING SUBTYPES, Molecular pharmacology, 44(5), 1993, pp. 1046-1050
At least three subtypes of alpha-bungarotoxin-sensitive acetylcholine
receptors (alphaBgt-sensitive AChRs) exist in chick brain and retina.
All may contain previously unknown structural subunits. One subtype co
ntains alpha7 subunits. Another contains alpha8 subunits. A third cont
ains both alpha7 and alpha8 subunits. In this article, we describe, fo
r the first time, the pharmacological characterization of alpha7 AChRs
and alpha8 AChRs immunoisolated from chick retina. Pharmacologically,
the alpha8 AChRs exhibit two classes of binding sites, the high affin
ity of which have higher affinity for most cholinergic ligands than do
alpha7 AChRs. These differences are most accentuated for ACh (approxi
mately 5400-fold), decamethonium (approximately 1400-fold), 1,1,-dimet
hyl-4 phenylpiperazinium (approximately 200-fold), atropine (approxima
tely 200-fold), nicotine (approximately 100-fold), and tetramethylammo
nium (approximately 100-fold). The alpha8 AChR low affinity sites exhi
bit affinities that are similar but not identical to that of alpha7 AC
hRs. Many of the pharmacological differences between the alpha7 AChRs
and alpha8 AChRs can be attributed to the limited differences between
the amino acid sequences of the N-terminal region of the alpha7 and al
pha8 subunits because expressed alpha7 homomers and alpha8 homomers al
so exhibit these characteristic differences.1