Conantokin is a distinct family of conotoxin superfamily. Its members share considerable overall sequence homology. Their defining attributes include a high relative content of gamma-carboxyglutamic acid (Gla). They are generally devoid of disufide-loop contrasted with other conotoxins (except for conantokin-R). Upon binding to metal ions, the content of alpha-helix conformation increases in different degrees. They inhibit NMDA (N-methyl-D-aspartate) receptors; moreover, different conantokin species present different NMDA receptor subunit specificity. It can induce sleep-like symptoms in young mice when delivered intracranially. Analysis of sequences and structures indicates that the high conserved residues of these peptides are determinative in their structures and functions. In this article, the relationships of their structures and functions are reviewed in detail.
Calcium Channel Blockers ; pharmacology ; Conotoxins ; chemistry ; pharmacology ; Humans ; Mollusk Venoms ; chemistry ; physiology ; Peptides ; chemistry ; physiology ; Receptors, N-Methyl-D-Aspartate ; antagonists & inhibitors ; Structure-Activity Relationship

Calcium ions are implicated in a variety of physiological functions, including enzyme activity, membrane excitability, neurotransmitter release, and synaptic transmission, etc. Calcium antagonists have been known to be effective for the treatment of exertional angina and essential hypertension. Selective and nonselective voltage-dependent calcium channel blockers also have inhibitory action on the acute and tonic pain behaviors resulting from thermal stimulation, subcutaneous formalin injection and nerve injury. This study was undertaken to investigate the effects of iontophoretically applied Ca++ and its antagonists on the responses of WDR (wide dynamic range) cells to sensory inputs. The responses of WDR cells to graded electrical stimulation of the afferent nerve and also to thermal stimulation of the receptive field were recorded before and after iontophoretical application of Ca++, EGTA, Mn++, verapamil, omega-conotoxin GVIA, omega-conotoxin MVIIC and omega-agatoxin IVA. Also studied were the effects of a few calcium antagonists on the C-fiber responses of WDR cells sensitized by subcutaneous injection of mustard oil (10%). Calcium ions and calcium channel antagonists (Mn++, verapamil, omega-conotoxin GVIA & omega-agatoxin IVA) current-dependently suppressed the C-fiber responses of WDR cells without any significant effects on the A-fiber responses. But omega-conotoxin MVIIC did not have any inhibitory actions on the responses of WDR cell to A-fiber, C-fiber and thermal stimulation. Iontophoretically applied EGTA augmented the WDR cell responses to C-fiber and thermal stimulations while spinal application of EGTA for about 20 ~ 30 min strongly inhibited the C-fiber responses. The augmenting and the inhibitory actions of EGTA were blocked by calcium ions. The WDR cell responses to thermal stimulation of the receptive field were reduced by imtophoretical application of Ca++, verapamil, omega -agatoxin IVA, and omega-conotoxin GVIA but not by omega-conotoxin MVIIC. The responses of WDR cells to C-fiber stimulation were augmented after subcutaneous injection of mustard oil (10%, 0.15 ml) into the receptive field and these sensitized C-fiber responses were strongly suppressed by iontophoretically applied Ca++, verapamil, omega-conotoxin GVIA and omega-agatoxin IVA. These experimental findings suggest that in the rat spinal cord, L-, N-, and P-type, but not Q-type, voltage-sensitive calcium channels are implicated in the calcium antagonist-induced inhibition of the normal and the sensitized responses of WDR cells to C-fiber and thermal stimulation, and that the suppressive effect of calcium and augmenting action of EGTA on WDR cell responses are due to changes in excitability of the cell.
Animals ; Calcium Channel Blockers* ; Calcium Channels* ; Calcium* ; Egtazic Acid ; Electric Stimulation ; Formaldehyde ; Hypertension ; Injections, Subcutaneous ; Ions ; Iontophoresis ; Membranes ; Mustard Plant ; Neurotransmitter Agents ; omega-Agatoxin IVA ; omega-Conotoxin GVIA ; omega-Conotoxins ; Posterior Horn Cells* ; Rats* ; Spinal Cord ; Synaptic Transmission ; Verapamil

The present study was designed to establish comparatively the inhibitory effects of cilnidipine (CNP), nifedipine (NIF), and omega-conotoxin GVIA (CTX) on the release of CA evoked by cholinergic stimulation and membrane depolarization from the isolated perfused model of the rat adrenal medulla. CNP (3 micrometer), NIF (3 micrometer), and CTX (3 micrometer) perfused into an adrenal vein for 60 min produced greatly inhibition in CA secretory responses evoked by ACh (5.32 x 10(-3) M), DMPP (10(-4) M for 2 min), McN-A-343 (10(-4) M for 2 min), high K+ (5.6 x 10(-2) M), Bay-K-8644 (10(-5) M), and cyclopiazonic acid (10(-5) M), respectively. For the CA release evoked by ACh and Bay-K-8644, the following rank order of potency was obtained: CNP > NIF > CTX. The rank order for the CA release evoked by McN-A-343 and cyclopiazonic acid was CNP > NIF > CTX. Also, the rank orders for high K+ and for DMPP were NIF > CTX > CNP and NIF > CNP > CTX, respectively. Taken together, these results demonstrate that all voltage-dependent Ca2+ channels (VDCCs) blockers of cilnidipine, nifedipine, and omega-conotoxin GVIA inhibit greatly the CA release evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors and the membrane depolarization without affecting the basal release from the isolated perfused rat adrenal gland. It seems likely that the inhibitory effects of cilnidipine, nifedipine, and omega-conotoxin GVIA are mediated by the blockade of both L- and N-type, L-type only, and N-type only VDCCs located on the rat adrenomedullary chromaffin cells, respectively, which are relevant to Ca2+ mobilization. It is also suggested that N-type VDCCs play an important role in the rat adrenomedullary CA secretion, in addition to L-type VDCCs.
(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethylammonium Chloride ; 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester ; Adrenal Glands ; Adrenal Medulla* ; Animals ; Calcium Channels ; Calcium Channels, L-Type ; Calcium Channels, N-Type ; Chromaffin Cells ; Dimethylphenylpiperazinium Iodide ; Membranes ; Nifedipine* ; omega-Conotoxin GVIA* ; omega-Conotoxins* ; Rats* ; Veins

The aim of this study was to investigate the role of Ca2+-channel blockers in norepinephrine (NE) release from rat hippocampus. Slices and synaptosomes were incubated with [3H]-NE and the releases of the labelled products were evoked by 25 mM KCl stimulation. Nifedipine, diltiazem, nicardipine, flunarizine and pimozide did not affect the evoked and basal release of NE in the slice. But, diltiazem, nicardipine and flunarizine decreased the evoked NE release with a dose-related manner without any change of the basal release from synaptosomes. Also, a large dose of pimozide produced modest decrement of NE release. omega-conotoxin (CTx) GVIA decreased the evoked NE release in a dose-dependent manner without changing the basal release. And omega-CTxMVIIC decreased the evoked NE release in the synaoptosomes without any effect in the slice, but the effect of decrement was far less than that of omega-CTxGVIA. In interaction experiments with omega-CTxGVIA, omega-CTxMVIIC slightly potentiated the effect of omega-CTxGVIA on NE release in the slice and synaptosomal preparations. These results suggest that the NE release in the rat hippocampus is mediated mainly by N-type Ca2+-channels, and that other types such as L-, T- and/or P/Q-type Ca2+-channels could also be participate in this process.
Animals ; Diltiazem ; Flunarizine ; Hippocampus ; Nicardipine ; Nifedipine ; Norepinephrine* ; omega-Conotoxins ; Pimozide ; Rats* ; Synaptosomes*

Animals ; Calcium ; metabolism ; Cell Hypoxia ; Cells, Cultured ; Hippocampus ; cytology ; Neurons ; drug effects ; metabolism ; Rats ; Rats, Wistar ; omega-Conotoxins ; pharmacology

Amino Acid Sequence ; Animals ; Calcium Channel Blockers ; pharmacology ; Calcium Channels ; drug effects ; Humans ; Molecular Sequence Data ; Structure-Activity Relationship ; omega-Conotoxins ; chemistry ; pharmacology

Excitatory amino acid (EAA) and substance P (SP) have been known to be primary candidates for nociceptive neurotransmitter in the spinal cord, and calcium ions are implicated in processing of the sensory informations mediated by EAA and SP in the spinal cord. In this study, we examined how Ca2+ modified the responses of dorsal horn neurons to single or combined iontophoretical application of EAA and SP in the rat. All the LT cells tested responded to kainate, whereas about 55% of low threshold (LT) cells responded to iontophoretically applied NMDA. NMDA and kainate excited almost all wide dynamic range (WDR) cells. These NMDA- and kainate-induced WDR cell responses were augmented by iontophoretically applied EGTA, but suppressed by Ca2+, Mn2+ verapamil and omega-conotoxin GVTA, effect of verapamil being more prominent and well sustained. Ca2+ and Mn2+ antagonized the augmenting effect of EGTA. On the other hand, prolonged spinal application of EGTA suppressed the response of WDR cell to NMDA. SP had triple effects on the spontaneous activity as well as NMDA-induced responses of WDR cells: excitation, inhibition and no change. EGTA augmented, but Ca2+, Mn2+ and verapamil suppressed the increase in the NMDA-induced responses and spontaneous activities of WDR cells following iontophoretical application of SP. These results suggest that in the spinal cord, sensory informations mediated by single or combined action of EAA and SP can be modified by the change in calcium ion concentration.
Animals ; Calcium* ; Egtazic Acid ; Excitatory Amino Acids* ; Hand ; Ions ; Iontophoresis ; Kainic Acid ; N-Methylaspartate ; Neurotransmitter Agents ; omega-Conotoxins ; Posterior Horn Cells* ; Rats* ; Spinal Cord ; Substance P ; Verapamil

Flavonoids have an ability to suppress various ion channels. We determined whether one of flavonoids, cyanidin-3-glucoside, affects adenosine 5'-triphosphate (ATP)-induced calcium signaling using digital imaging methods for intracellular free Ca2+ concentration ([Ca2+]i), reactive oxygen species (ROS) and mitochondrial membrane potential in PC12 cells. Treatment with ATP (100microM) for 90 sec induced [Ca2+]i increases in PC12 cells. Pretreatment with cyanidin-3-glucoside (1micro g/ml to 100microg/ml) for 30 min inhibited the ATP-induced [Ca2+]i increases in a concentration-dependent manner (IC50=15.3microg/ml). Pretreatment with cyanidin-3-glucoside (15microg/ml) for 30 min significantly inhibited the ATP-induced [Ca2+]i responses following removal of extracellular Ca2+ or depletion of intracellular [Ca2+]i stores. Cyanidin-3-glucoside also significantly inhibited the relatively specific P2X2 receptor agonist 2-MeSATP-induced [Ca2+]i responses. Cyanidin-3-glucoside significantly inhibited the thapsigargin or ATP-induced store-operated calcium entry. Cyanidin-3-glucoside significantly inhibited the ATP-induced [Ca2+]i responses in the presence of nimodipine and omega-conotoxin. Cyanidin-3-glucoside also significantly inhibited KCl (50 mM)-induced [Ca2+]i increases. Cyanidin-3-glucoside significantly inhibited ATP-induced mitochondrial depolarization. The intracellular Ca2+ chelator BAPTA-AM or the mitochondrial Ca2+ uniporter inhibitor RU360 blocked the ATP-induced mitochondrial depolarization in the presence of cyanidin-3-glucoside. Cyanidin-3-glucoside blocked ATP-induced formation of ROS. BAPTA-AM further decreased the formation of ROS in the presence of cyanidin-3-glucoside. All these results suggest that cyanidin-3-glucoside inhibits ATP-induced calcium signaling in PC12 cells by inhibiting multiple pathways which are the influx of extracellular Ca2+ through the nimodipine and omega-conotoxin-sensitive and -insensitive pathways and the release of Ca2+ from intracellular stores. In addition, cyanidin-3-glucoside inhibits ATP-induced formation of ROS by inhibiting Ca2+-induced mitochondrial depolarization.
Adenosine ; Adenosine Triphosphate ; Animals ; Calcium ; Calcium Signaling ; Flavonoids ; Ion Channels ; Ion Transport ; Membrane Potential, Mitochondrial ; Nimodipine ; omega-Conotoxins ; PC12 Cells* ; Reactive Oxygen Species ; Receptors, Purinergic P2X2 ; Thapsigargin

Nimopidine, one of dihydropyridine derivatives, has been widely used to pharmacologically identify L-type Ca currents. In this study, it was tested if nimodipine is a selective blocker for L-type Ca currents in sensory neurons and heterologous system. In mouse dorsal root ganglion neurons (DRG), low concentrations of nimodipine (<10 muM), mainly targeting L-type Ca currents, blocked high-voltage-activated calcium channel currents by apprx38%. Interestingly, high concentrations of nimodipine (>10 muM) further reduced the "residual" currents in DRG neurons from alpha1E knock-out mice, after blocking L-, N- and P/Q-type Ca currents with 10 muM nimodipine, 1 muM omega-conotoxin GVIA and 200 nM omega-agatoxin IVA, indicating inhibitory effects of nimodipine on R-type Ca currents. Nimodipine (>10 muM) also produced the inhibition of both low-voltage-activated calcium channel currents in DRG neurons and alpha1B and alpha1E subunit based Ca channel currents in heterologous system. These results suggest that higher nimodipine (>10 muM) is not necessarily selective for L-type Ca currents. While care should be taken in using nimodipine for pharmacologically defining L-type Ca currents from native macroscopic Ca currents, nimodipine (>10 muM) could be a useful pharmacological tool for characterizing R-type Ca currents when combined with toxins blocking other types of Ca channels.
Animals ; Calcium Channels ; Calcium* ; Diagnosis-Related Groups ; Ganglia, Spinal ; Mice ; Mice, Knockout ; Neurons ; Nimodipine* ; omega-Agatoxin IVA ; omega-Conotoxin GVIA ; Sensory Receptor Cells

Protease-activated receptor (PAR)-2 is expressed in endothelial cells and vascular smooth muscle cells. It plays a crucial role in regulating blood pressure via the modulation of peripheral vascular tone. Although some reports have suggested involvement of a neurogenic mechanism in PAR-2-induced hypotension, the accurate mechanism remains to be elucidated. To examine this possibility, we investigated the effect of PAR-2 activation on smooth muscle contraction evoked by electrical field stimulation (EFS) in the superior mesenteric artery. In the present study, PAR-2 agonists suppressed neurogenic contractions evoked by EFS in endothelium-denuded superior mesenteric arterial strips but did not affect contraction elicited by the external application of noradrenaline (NA). However, thrombin, a potent PAR-1 agonist, had no effect on EFS-evoked contraction. Additionally, omega-conotoxin GVIA (CgTx), a selective N-type Ca2+ channel (I(Ca-N)) blocker, significantly inhibited EFS-evoked contraction, and this blockade almost completely occluded the suppression of EFS-evoked contraction by PAR-2 agonists. Finally, PAR-2 agonists suppressed the EFS-evoked overflow of NA in endothelium-denuded rat superior mesenteric arterial strips and this suppression was nearly completely occluded by omega-CgTx. These results suggest that activation of PAR-2 may suppress peripheral sympathetic outflow by modulating activity of I(Ca-N) which are located in peripheral sympathetic nerve terminals, which results in PAR-2-induced hypotension.
Animals ; Blood Pressure ; Endothelial Cells ; Hypotension* ; Mesenteric Arteries ; Mesenteric Artery, Superior ; Muscle, Smooth ; Muscle, Smooth, Vascular ; Norepinephrine ; omega-Conotoxin GVIA ; Rats ; Receptor, PAR-2 ; Thrombin