Nicotinic Acetylcholine Receptors Assembled from the α7 and β3 Subunits

doi:10.1074/jbc.274.26.18335

Nicotinic Acetylcholine Receptors Assembled from the α7 and β3 Subunits*

From the ^‡Istituto Pasteur-Fondazione Cenci Bolognetti and Dipartimento di Medicina Sperimentale Universita’ di Roma “La Sapienza”, ^¶Laboratorio di Biofisica, Centro Ricerca Sperimentale Istituto Regina Elena, via delle Messi d’ Oro 156, 00158 Roma, Italy, and ^§Département de Biochimie, Université de Genève, 1211 Genève 4, Switzerland

Abstract

Intracellular recordings were performed in voltage-clamped Xenopus oocytes upon injection with a mixture of cDNAs encoding the β3 and mutant α7 (^L247Tα7) neuronal nicotinic acetylcholine receptor (nAChR) subunits. The expressed receptors maintained sensitivity to methyllycaconitine and to α-bungarotoxin but exhibited a functional profile strikingly different from that of the homomeric^L247Tα7 receptor. The heteromeric^L247Tα7β3 nAChR had a lower apparent affinity and a faster rate of desensitization than ^L247Tα7 nAChR, exhibited nonlinearity in the I-V relationship, and was inhibited by 5-hydroxytryptamine, much like wild type α7 (^WTα7) nAChR. Single channel recordings in cell-attached mode revealed unitary events with a slope conductance of 19 picosiemens and a lifetime of 5 ms, both values being much smaller than those of the homomeric receptor channel. Upon injection with a mixture of ^WTα7 and β3 cDNAs, clear evidence was obtained for the plasma membrane assembly of heteromeric nAChRs, although ACh could not activate these receptors. It is concluded that β3, long believed to be an orphan subunit, readily co-assembles with other subunits to form heteromeric receptors, some of which may be negative regulators of cholinergic function.

Footnotes

↵* This work was supported by grants from Ministero Università Ricerca Scientifica e Tecnologica (to F. E.), by grants from the Swiss National Science Foundation (to M. B.), and by a Telethon fellowship (222/bi (to E. P.)).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵‖ To whom reprint requests should be addressed. Biochemistry/Sciences II, 30, quai Ernest Ansermet, 1211 Geneva 4, Switzerland. Fax: 41 22 702 6483; E-mail:marc.ballivet{at}biochem.unige.ch.
Abbreviations:

nAChR

neuronal nicotinic acetylcholine receptor

MLA

methyllycaconitine

α-Bgt

α-bungarotoxin

5HT

5-hydroxytryptamine

WT

wild type

MTS

methanethiosulfonate

MTSEA

MTS ethylamine hydrobromide

MTSET

MTS ethyltrimethylammonium bromide

MTSES

sodium MTS ethylsulfonate

PP

pipette potential

pS

picosiemens
- Received February 9, 1999.
- Revision received April 15, 1999.
The American Society for Biochemistry and Molecular Biology, Inc.