Abstract
We used equilibrium binding analysis to characterize the agonist binding properties of six different rat neuronal nicotinic receptor subunit combinations expressed in Xenopus laevisoocytes. The α4β2 receptor bound [3H]cytisine with aK d app of 0.74 ± 0.14 nm. The rank order ofK i app values of additional nicotinic ligands, determined in competition assays, was cytisine < nicotine < acetylcholine < carbachol < curare. These pharmacological properties of α4β2 expressed in oocytes are comparable to published values for the high affinity cytisine binding site in rat brain (α4β2), demonstrating that rat neuronal nicotinic receptors expressed in X.laevis oocytes display appropriate pharmacological properties. Use of [3H]epibatidine allowed detailed characterization of multiple neuronal nicotinic receptor subunit combinations. K d appvalues for [3H]epibatidine binding were 10 pm for α2β2, 87 pm for α2β4, 14 pm for α3β2, 300 pm for α3β4, 30 pm for α4β2, and 85 pm for α4β4. Affinities for six additional agonists (acetylcholine, anabasine, cytisine, 1,1-dimethyl-4-phenylpiperazinium, lobeline, and nicotine) were determined in competition assays. The β2-containing receptors had consistently higher affinities for these agonists than did β4-containing receptors. Particularly striking examples are the affinities displayed by α2β2 and α2β4, which differ in 1,1-dimethyl-4-phenylpiperazinium, nicotine, lobeline, and acetylcholine affinity by 120-, 86-, 85-, and 61-fold, respectively. Although smaller differences in affinity could be ascribed to different α subunits, the major factor in determining agonist affinity was the nature of the β subunit.
Footnotes
- Received July 10, 1998.
- Accepted September 14, 1998.
-
Send reprint requests to: Dr. Charles W. Luetje, Department of Molecular and Cellular Pharmacology (R-189), University of Miami School of Medicine, P.O. Box 016189, Miami, FL 33101. E-mail:cluetje{at}chroma.med.miami.edu
-
This work was supported by a grant to C.W.L. from the National Institute on Drug Abuse (DA08102). M.J.P. was supported in part by T32-HL07188. Portions of this work have been presented in preliminary form [Parker MJ and Luetje CW (1996) Soc Neurosci Abstr 22:1271; Parker MJ and Luetje CW (1997) Soc Neurosci Abstr 23:385].
- The American Society for Pharmacology and Experimental Therapeutics
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|