Blockage of muscle and neuronal nicotinic acetylcholine receptors by fluoxetine (Prozac)

Abstract

Fluoxetine (Prozac), a widely used antidepressant, is said to exert its medicinal effects almost exclusively by blocking the serotonin uptake systems. The present study shows that both muscle and neuronal nicotinic acetylcholine receptors are blocked, in a noncompetitive and voltage-dependent way, by f luoxetine, which also increases the rate of desensitization of the nicotinic receptors. Because these receptors are very widely distributed in the both central and peripheral nervous systems, the blocking action of f luoxetine on nicotinic receptors may play an important role in its antidepressant and other therapeutical effects. Our findings will help to understand the mode of action of f luoxetine, and they may also help to develop more specific medicinal drugs.Nicotinic acetylcholine receptors (nAcChoRs) mediate the transmission of signals across the vertebrate neuromuscular junction as well as across central and peripheral synapses (1, 2). Another widely distributed system is that in which serotonin (5-hydroxytryptamine, 5HT) is the neurotransmitter (3, 4), and it is now evident that the two systems are not completely specific. For example, dopamine activates 5HT receptors (5), and there are marked cross-interactions between serotonergic and cholinergic systems. For instance, atropine, a muscarinic antagonist, blocks both acetylcholine (AcCho) receptors and 5HT receptors in snail neurons (6); dihydro-␤-erythroidine and tubocurarine, nicotinic antagonists, block 5HT 3 receptors (7) and serotonin, as well as various serotonergic agonists and antagonists, block in a noncompetitive manner both muscle and neuronal nAcChoRs (8-10). Finally, 5HT acts as an antagonist on wild-type neuronal ␣ 7 nAcChoR, but it acts as an agonist on the ␣ 7 nAcChoR mutated in the M2 transmembrane region (11,12). Because fluoxetine (Prozac), a highly efficient inhibitor of 5HT uptake, is extensively used in the treatment of depression, eating disorders, and other diseases of the brain (13), we decided to see if, like other serotonergic agents, fluoxetine would alter the function of nAcChoRs. MATERIALS AND METHODSThe experiments were performed on voltage-clamped Xenopus oocytes expressing muscle ␣ 1 ␤ 1 ␥␦ or neuronal (␣ 2 ␤ 4 or ␣ 3 ␤ 4 ) nAcChoRs. The complementary RNA preparation, oocyte injection, and electrophysiological recordings have been described elsewhere (8, 9). Briefly, RNAs encoding mouse muscle (␣ 1 , ␤ 1 , ␥, and ␦) or rat neuronal (␣ 2 , ␣ 3 , and ␤ 4 ) nAcChoR subunits were transcribed in vitro. Equal quantities of cRNA subunits were combined to obtain ␣ 1 ␤ 1 ␥␦, ␣ 2 ␤ 4 , and ␣ 3 ␤ 4 nAcChoR subtypes. Xenopus laevis oocytes were dissected from the ovary and maintained at 16ЊC in Barth's solution containing 88 mM NaCl, 1 mM KCl, 0.33 mM Ca(NO 3 ) 2 , 0.41 mM CaCl 2 , 0.82 mM MgSO 4 , 2.4 mM NaHCO 3 , 5 mM Hepes (pH 7.4; NaOH), and 0.1 mg͞ml gentamicin sulfate. The next day each oocyte was injected with 0.5-50 ng of the corresponding cRNA mixture in a volume of 50 nl water, and about 2 days later the follicullar ...

Combined actions of zinc and fluoxetine on nicotinic acetylcholine receptors

“…10,16 Briefly, cRNAs encoding the mouse muscle (a1, b1, g and d) and rat neuronal (a4 and b4) nAChR subunits were transcribed in vitro and mixtures, with equal quantities of RNA subunits, were prepared to express a1b1gd and a4b4 combinations. All experimental manipulations were made according to the ethical policies of animal care and handling of the National University.…”

“…12,16 Figure 1 illustrates an example of these effects on oocytes expressing neuronal a4b4 nAChRs. An inward current was elicited with ACh, and after the peak had been reached 200 mM zinc was co-applied with the ACh (Figure 1a, a).…”

“…For instance, they are modulated by cations, [5][6][7][8] 5-HT, 9-13 various agonists and antagonists of different types of 5-HT receptors, [9][10][11][12]14 as well as inhibitors of monoamine transporters that are used as antidepressants. 9,12,[15][16][17][18][19][20] The most common action of clinically used antidepressants on nAChRs appears to be a noncompetitive inhibitory process, 9,12,[15][16][17][18][19][20] and it is probable that this action contributes to improving depressed mood states. 21 On the other hand, zinc is contained in neurons that are widely distributed throughout the nervous system; 22 and it is released from GABAergic and glutamatergic nerve endings, 23,24 reaching an extracellular concentration of B300 mM.…”

Nicotinic acetylcholine receptors as targets for antidepressants

“…13,16 More recent studies have characterized newer, more selective monoamine reuptake inhibitors including fluoxetine, [17][18][19] sertraline, paroxetine, nefazodone, 20 nisoxetine, citalopram, nomifensine, 21 and GBR-12909 22 as nAChR antagonists. Perhaps one of the most interesting antidepressants demonstrated to have nAChR inhibitory activity is the atypical antidepressant, bupropion.…”

Inhibition of G Protein-Activated Inwardly Rectifying K+ Channels by Various Antidepressant Drugs

“…In contrast, the interaction of antidepressants with muscarinic, a 1 adrenergic, and H 1 histamine receptors is involved in some of the adverse side effects (Baldessarini, 2001). It has also been shown that antidepressants inhibit the functions of several other receptors and ion channels, such as 5-HT 2C (Ni and Miledi, 1997) and 5-HT 3 receptors (Fan, 1994), nicotinic acetylcholine receptors (García-Colunga et al, 1997;Maggi et al, 1998), N-methyl-D-aspartate (NMDA) receptor channels (Sernagor et al, 1989), P2X 2 receptors (Nakazawa et al, 1999), voltage-gated Ca 2 þ , Na þ , and K þ channels (Ogata et al, 1989;Mathie et al, 1998;Pancrazio et al, 1998;Teschemacher et al, 1999;Yeung et al, 1999;Deák et al, 2000;Choi et al, 2001;Cuellar-Quintero et al, 2001), Ca 2 þ -activated K þ channels (Kamatchi and Ticku, 1991;Lee et al, 1997;Dreixler et al, 2000;Terstappen et al, 2001), and Cl À channels (Maertens et al, 1999(Maertens et al, , 2002. The effects might also be involved in the molecular and cellular mechanisms underlying some of the therapeutic effects and side effects of various antidepressants.…”