COMPARATIVE STRUCTURE OF HUMAN NEURONAL ALPHA-2-ALPHA-7 AND BETA-2-BETA-4 NICOTINIC ACETYLCHOLINE-RECEPTOR SUBUNITS AND FUNCTIONAL EXPRESSION OF THE ALPHA-2, ALPHA-3, ALPHA-4, ALPHA-7, BETA-2, AND BETA-4 SUBUNITS

cDNA clones encoding human neuronal nicotinic acetylcholine receptor a lpha 2, alpha 3, alpha 4, alpha 5, alpha 6, alpha 7, beta 2, beta 3, a nd beta 4 subunits were isolated from brainstem, hippocampus, prefront al cortex, substantia nigra, thalamus, and IMR32 libraries. Human alph a 2 and alpha 6 and full-length beta 3 and beta 4 clones have not been previously reported. Deduced amino acid sequences of the alpha 2, alp ha 6, beta 3, and beta 4 predicted mature peptides are 503 residues (5 6.9 kDa), 464 residues (53.7 kDa), 440 residues (50.8 kDa), and 477 re sidues (54.1 kDa), respectively. These sequences show 84 (alpha 2), 87 (alpha 6), 89 (beta 3), and 84% (beta 4) identity to the correspondin g rat sequences. The amino termini of the human alpha 2 and beta 3 mat ure peptides contain 23 and six additional residues, respectively, com pared to those of rat alpha 2 and beta 3. Recombinant receptors were e xpressed in Xenoptls laevis oocytes injected with in vitro transcripts encoding either alpha 7 alone or alpha 2, alpha 3, or alpha 4 in pair wise combination with beta 2 or beta 4. Inward currents were elicited by the application of acetylcholine (1-100 ,mu M) and other agonists; these responses were blocked 65-97% by application of 10 mu M d-tubocu rare, confirming functional expression of human nicotinic receptors.