[Abstract Title]. - Society for Neuroscience

Program#/Poster#: 233.20/C22
Topic: B.02.c. Nicotinic acetylcholine receptors: regulation and function
Support: the Peter F. McManus Foundation to WNG
PO1 DA019695
NIH grants NS043782
DA019695
DA13602
Title: Mechanims underlying nicotine-induced upregulation of nicotinic acetylcholine receptors
(nAChRs)
Authors: *A. P. GOVIND 1 , H. S. WALSH 2 , Y. VALLEJO 3 , V. MCSWEEN 1 , W. GREEN 1 ;
1 Neurobio., Univ. of Chicago, Chicago, IL; 2 UCtech, Univ. of Chicago, Chicago, IL; 3 Natl. Inst.
of Neurolog. Disorders and Stroke, Bethesda, MD
Abstract: Chronic nicotine exposure upregulates the number of high-affinity agonist binding
sites found on α4β2, as well as α3- and α6-containing nicotinic acetylcholine receptors
(nAChRs). We have investigated whether nicotine-induced upregulation results from changes in
nAChR numbers or other mechanisms. Both nicotine treatment and a temperature shift from 37
to 30°C caused similar increases in the number of high-affinity binding sites on α6β2 and α3β2
nAChRs. While the temperature-induced increase in high-affinity binding sites corresponded
with an increase in nAChR numbers, no change in nAChRs, either cell-surface or intracellular
pools, was observed after nicotine treatment. α4β2 receptors differed from the other nAChRs in
that the nicotine upregulation had two different effects on α4β2 nAChRs. Like the other
nAChRs, nicotine-induced increases of α4β2 high-affinity binding sites were largely independent
of a change in receptor number. These upregulated receptors appeared to undergo a
conformational change caused by nicotine treatment as evidenced by: 1) a change in α4 subunit
migration on SDS-PAGE and 2) a change in the binding of subunit-specific antibodies and other
ligands. However, nicotine did cause a significant increase in receptor numbers that
corresponded to a fraction of the increase in high-affinity binding sites. The increased α4β2
receptor numbers coincided with a slowing of the degradation rate of intracellular β subunits.
Additional evidence for two different mechanisms underlying α4β2 receptor nicotine-induced
upregulation was the reversal of upregulation. Removal of nicotine after nicotine-induced
upregulation caused upregulated high-affinity binding sites to decay at two very different rates.
The fast rate (tau~1.5 hrs) corresponded to the fraction of high-affinity binding sites independent
of a change in nAChR numbers and may be the reversal of a nicotine-induced conformational
change. The slow decay rate (tau~18 hrs) corresponded with the increased number of nAChRs
and was consistent with nAChR degradation rates.