An electrophysiological study of muscarinic and nicotinic receptors of rat paratracheal ganglion neurons and their inhibition by Z‐338

Abstract

1 To study the mechanisms involved in the action of Z-338, a newly synthesized gastroprokinetic agent, experiments were performed with the paratracheal ganglion cells acutely dissociated from 2-week-old Wistar rats. The e ects of Z-338 on both nicotinic and muscarinic responses of the ganglion cells were studied by nystatin perforated patch recording con®guration under the currentand voltage-clamp conditions. 2 Acetylcholine (ACh) or nicotine, and muscarine or oxotremorine-M (OX-M) induced membrane depolarization with rapid and slow time courses respectively, followed by repetitive generation of action potentials in the ganglion cell. Corresponding to the membrane depolarization induced by cholinergic agents, ACh induced biphasic inward currents with rapid and slow time courses under the voltage-clamp condition. Nicotine and muscarine or OX-M evoked inward currents with rapid and slow time courses, respectively. The rapid and slow inward currents were accompanied by increase and decrease in the membrane conductance, respectively. In addition, OX-M dosedependently suppressed the M-type K + current evoked in response to hyperpolarizing voltage-steps from V H of 725 mV to 750 mV, indicating that the activation of muscarinic acetylcholine receptors inhibits M-type K + current, thus inducing inward current in the ganglion cell. 3 Z-338 competitively suppressed the inward currents induced by OX-M through M 1 ACh receptor, and uncompetitively suppressed the currents induced by nicotine. 4 The inhibitory actions of Z-338 on the membrane depolarization and corresponding inward currents mediated by M 1 -muscarinic and neuronal nicotinic ACh receptors in the isolated ganglion cells were discussed in relation to the inhibitory actions on autoreceptors in the parasympathetic nerve terminals, which would explain the gastroprokinetic actions of Z-338.

Effects of Z-338, a novel gastroprokinetic agent, on the actions of excitatory and inhibitory neurotransmitters on neurons in area postrema

“…It is well documented, however, that Z-338 acts antagonistically on mAChRs (M1 and M2) and nAChRs (Ogishima et al, 2000;Kanemoto et al, 2002), and the present results support this. In addition to the inhibitory action of Z-338 on nAChRs, the present study revealed that Z-338 also inhibits GABA-induced current in a competitive manner in AP neurons.…”

“…In the rat paratracheal ganglion, we reported that activation of nAChRs and mAChRs induced inward currents with rapid and slow time courses, and that Z-338 inhibited mAChR-and nAChR-mediated inward currents competitively and uncompetitively, respectively (Kanemoto et al, 2002). AP neurons are considered to possess nAChRs but not mAChRs (Strominger et al, 2001), and in the present experiments Z-338 inhibited nicotine-induced inward currents as in the case of paratracheal ganglion cells.…”

“…In isolated paratracheal ganglion cells, ACh induces slow and fast inward currents through activation of M1-mAChR and neuronal nicotinic ACh receptors (nAChR). Z-338 inhibits slow and fast inward currents induced by ACh in a competitive and noncompetitive manner, respectively (Kanemoto et al, 2002). All these findings are consistent with the view that Z-338 facilitates excitatory neuroeffector transmission in the stomach by increasing ACh release from cholinergic nerve terminals via inhibition of pre-junctional M1-and M2-mAChR or nAChR.…”

“…Furthermore, our recent study indicates that rat stomach receives efferent neural input from AP and electrical stimulation of AP neurons relaxes the stomach in rat, thereby suggesting that some functional roles of AP neurons in the regulation of gastric motility (Kawachi et al, 2008). Z-338 has well documented excitatory but not inhibitory action on stomach motility through the peripheral autonomic nervous system (Ueki et al, 1998;Nakajima et al, 2000;Kanemoto et al, 2002;Morita et al, 2002). The actions of Z-338 on central and peripheral autonomic nervous system, taken together, would therefore explain the observations that Z-338 induces postmeal relaxation and improve postprandial fullness in patients with functional dyspepsia (Tack et al, 2002).…”

Cholinergic EPSCs and their potentiation by bradykinin in single paratracheal ganglion neurons attached with presynaptic boutons

“…According to the previous report, mecamylamine (10 Ϫ8 ϳ10 Ϫ4 M) inhibits nicotine-induced current with an IC 50 of 1.7 ϫ 10 Ϫ6 M in dissociated PTG neurons (Kanemoto et al 2002), and the currents are fully blocked by mecamylamine at a concentration larger than 10 Ϫ4 M. In addition, 50 M mecamylamine reduced cholinergic EPSC amplitudes by 33% in central nicotinic receptors (Chu et al 2000), and 10ϳ20 M mecamylamine blocked 62-79% of the EPSC in other ganglionic nicotinic receptors (Nong et al 1999). Thus the inhibitions by mecamylamine on EPSCs and nicotine-induced currents are comparative.…”