Abstract
Subtypes (1–4) of the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are widely expressed in the central and peripheral nervous systems, as well as the cells of smooth muscles in many organs. They mainly serve to regulate cellular excitability in these tissues. The HCN channel blocker ZD7288 has been shown to reduce apomorphine-induced conditioned taste aversion on saccharin preference in rats suggesting potential antinausea/antiemetic effects. Currently, in the least shew model of emesis we find that ZD7288 induces vomiting in a dose-dependent manner, with maximal efficacies of 100% at 1 mg/kg (i.p.) and 83.3% at 10 µg (i.c.v.). HCN channel subtype (1–4) expression was assessed using immunohistochemistry in the least shrew brainstem dorsal vagal complex (DVC) containing the emetic nuclei (area postrema (AP), nucleus tractus solitarius and dorsal motor nucleus of the vagus). Highly enriched HCN1 and HCN4 subtypes are present in the AP. A 1 mg/kg (i.p.) dose of ZD7288 strongly evoked c-Fos expression and ERK1/2 phosphorylation in the shrew brainstem DVC, but not in the in the enteric nervous system in the jejunum, suggesting a central contribution to the evoked vomiting. The ZD7288-evoked c-Fos expression exclusively occurred in tryptophan hydroxylase 2-positive serotonin neurons of the dorsal vagal complex, indicating activation of serotonin neurons may contribute to ZD7288-induced vomiting. To reveal its mechanism(s) of emetic action, we evaluated the efficacy of diverse antiemetics against ZD7288-evoked vomiting including the antagonists/inhibitors of: ERK1/2 (U0126), L-type Ca2+ channel (nifedipine); store-operated Ca2+ entry (MRS 1845); T-type Ca2+ channel (Z944), IP3R (2-APB), RyR receptor (dantrolene); the serotoninergic type 3 receptor (palonosetron); neurokinin 1 receptor (netupitant), dopamine type 2 receptor (sulpride), and the transient receptor potential vanilloid 1 receptor agonist, resiniferatoxin. All tested antiemetics except sulpride attenuated ZD7288-evoked vomiting to varying degrees. In sum, ZD7288 has emetic potential mainly via central mechanisms, a process which involves Ca2+ signaling and several emetic receptors. HCN channel blockers have been reported to have emetic potential in the clinic since they are currently used/investigated as therapeutic candidates for cancer therapy related- or unrelated-heart failure, pain, and cognitive impairment.
Highlights
Defensive processes such as nausea and vomiting protect vomitcompetent species avoid ingestion of toxic substances
The anatomical sites involved in emesis include the dorsal vagal complex (DVC) emetic nuclei contained in the brainstem [the area postrema (AP), nucleus tractus solitarius (NTS) and dorsal motor nucleus of the vagus (DMNX)], the enteric nervous system (ENS) and enterochromaffin cells of the gastrointestinal tract, vagal afferents which carry emetic input from the gastrointestinal tract to the brainstem NTS, as well as vagal efferents which project motor signals from the Dorsal motor nucleus of the vagus (DMNX) to the gastrointestinal tract (Darmani and Ray, 2009; Babic and Browning, 2014)
Our present study provides in vivo evidence that the Hyperpolarization-activated cyclic nucleotide-gated (HCN) blocker ZD7288 causes vomiting, a process that is partially dependent upon Ca2+ mobilization which may involve Ca2+ intracellular store release through IP3Rs and Ryanodine receptor (RyR), as well as extracellular Ca2+ entry via plasma membrane Ca2+ channels
Summary
Defensive processes such as nausea and vomiting protect vomitcompetent species avoid ingestion of toxic substances. Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are a class of voltage-gated ion-channels permeable to Na+ and K+ and constitutively open at voltages near the resting membrane potential (Benarroch, 2013; McGovern et al, 2014). They consist of four subtypes 1–4, and are expressed on excitable cells in the central and peripheral nervous systems. P.) can suppress apomorphine-induced conditioned taste aversion to saccharin preference and the apomorphine-evoked c-Fos expression in the rat area postrema (Shinpo et al, 2012) Based on these findings, the authors had suggested antinausea/antiemesis potential of ZD7288. 3.3% have reported nausea (Chaturvedi et al, 2013)
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