The α3* nAChRs, which are considered to be promising drug targets for problems such as pain, addiction, cardiovascular function, cognitive disorders etc., are found throughout the central and peripheral nervous system. The α-conotoxin (α-CTx) LvIA has been identified as the most selective inhibitor of α3β2 nAChRs known to date, and it can distinguish the α3β2 nAChR subtype from the α6/α3β2β3 and α3β4 nAChR subtypes. However, the mechanism of its selectivity towards α3β2, α6/α3β2β3, and α3β4 nAChRs remains elusive. Here we report the co-crystal structure of LvIA in complex with Aplysia californica acetylcholine binding protein (Ac-AChBP) at a resolution of 3.4 Å. Based on the structure of this complex, together with homology modeling based on other nAChR subtypes and binding affinity assays, we conclude that Asp-11 of LvIA plays an important role in the selectivity of LvIA towards α3β2 and α3/α6β2β3 nAChRs by making a salt bridge with Lys-155 of the rat α3 subunit. Asn-9 lies within a hydrophobic pocket that is formed by Met-36, Thr-59, and Phe-119 of the rat β2 subunit in the α3β2 nAChR model, revealing the reason for its more potent selectivity towards the α3β2 nAChR subtype. These results provide molecular insights that can be used to design ligands that selectively target α3β2 nAChRs, with significant implications for the design of new therapeutic α-CTxs.
Animals ; Aplysia ; Binding Sites ; Conotoxins ; chemistry ; Crystallography, X-Ray ; Humans ; Protein Structure, Quaternary ; Receptors, Nicotinic ; chemistry

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

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

The Conus venom is secreted by the duct and theca of venom. Most of conotoxins are composed of 10-40 amino acid residues with several disulfide bridges. They can specifically target neurotransmitter receptors including nAChRs, calcium ion channels, sodium ion channels and potassium ion channels, etc. Some conotoxins, such as that target N-Ca2+ channels, nAChR alpha9alpha10 subtype, TTX-R Na+ channels or NMDA receptors, have potent antinociceptive activities, omega-MVIIA, an Ca2+ channels blocker was approved by FDA in December, 2004 for marketing. Because of lower molecular weight and high specificity, conotoxins are the powerful pharmacology tools and potent analgesics without addiction. This review briefly summarizes the research progress of antinociceptive conotoxins and addresses on their targets and structure-activity relationships.
Analgesics ; pharmacology ; Calcium Channels ; drug effects ; Conotoxins ; pharmacology ; Sodium Channels ; drug effects ; Structure-Activity Relationship

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

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

Melittin-induced nociceptive responses are mediated by selective activation of capsaicin-sensitive primary afferent fibers and are modulated by excitatory amino acid receptor, cyclooxygenase, protein kinase C and serotonin receptor. The present study was undertaken to investigate the peripheral and spinal actions of voltage-gated calcium channel antagonists on melittin-induced nociceptive responses. Changes in mechanical threshold and number of flinchings were measured after intraplantar (i.pl.) injection of melittin (30microg/paw) into mid-plantar area of hindpaw. L-type calcium channel antagonists, verapamil [intrathecal (i.t.), 6 or 12microg; i.pl.,100 & 200microg; i.p., 10 or 30 mg], N-type calcium channel blocker, omega-conotoxin GVIA (i.t., 0.1 or 0.5microg; i.pl., 5microg) and P-type calcium channel antagonist, omega-agatoxin IVA (i.t., 0.5microg; i.pl., 5microg) were administered 20 min before or 60 min after i.pl. injection of melittin. Intraplantar pre-treatment and i.t. pre- or post-treatment of verapamil and omega-conotoxin GVIA dose-dependently attenuated the reduction of mechanical threshold, and melittin-induced flinchings were inhibited by i.pl. or i.t. pre-treatment of both antagonists. P-type calcium channel blocker, omega-agatoxin IVA, had significant inhibitory action on flinching behaviors, but had a limited effect on melittin-induced decrease in mechanical threshold. These experimental findings suggest that verapamil and omega-conotoxin GVIA can inhibit the development and maintenance of melittin-induced nociceptive responses.
Animals ; Calcium Channels* ; Calcium Channels, L-Type ; Calcium Channels, N-Type ; Calcium Channels, P-Type ; Calcium* ; Hyperalgesia ; Ions* ; Melitten ; Nociception* ; omega-Agatoxin IVA ; omega-Conotoxin GVIA ; Prostaglandin-Endoperoxide Synthases ; Protein Kinase C ; Rats* ; Receptors, Glutamate ; Serotonin ; Verapamil

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

The present study was attempted to investigate the effect of cilnidipine (FRC-8635), which is a newly synthesized novel dihydropyridine (DHP) type of organic Ca2 channel blockers, on secretion of catecholamines (CA) evoked by acetylcholine (ACh), high K, DMPP and McN-A-343 from the isolated perfused rat adrenal gland. Cilnidipine (1~10microM) perfused into an adrenal vein for 60 min produced relatively dose- and time-dependent inhibition in CA secretory responses evoked by ACh (5.32 10 3 M), DMPP (10 4 M for 2 min) and McN-A-343 (10 4 M for 2 min). However, lower dose of cilnidipine did not affect CA secretion by high K (5.6 10 2 M), higher dose of it reduced greatly CA secretion of high K. Cilnidipine itself did fail to affect basal catecholamine output. In the presence of cilnidipine (10microM), the CA secretory responses evoked by Bay-K-8644 (10microM), an activator of L-type Ca2 channels and cyclopiazonic acid (10microM), an inhibitor of cytoplasmic Ca2 -ATPase were also inhibited. Moreover, omega-conotoxin GVIA (1microM), a selective blocker of the N-type Ca2 channels, given into the adrenal gland for 60 min, also inhibited time-dependently CA secretory responses evoked by Ach, high K, DMPP, McN-A-343, Bay-K-8644 and cyclopiazonic acid. Taken together, these results demostrate that cilnidipine inhibits CA secretion evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors from the isolated perfused rat adrenal gland without affecting the basal release. However, at lower dose, cilnidipine did not affect CA release by membrane depolarization while at larger dose inhibited that. It seems likely that this inhibitory effect of cilnidipine is exerted by blocking both L- and N-type voltage-dependent Ca2 channels (VDCCs) on the rat adrenomedullary chromaffin cells, which is relevant to inhibition of both the Ca2 influx into the adrenal chromaffin cells and intracellular Ca2 release from the cytoplasmic store. It is thought that N-type VDCCs may play an important role in regulation of CA release from the rat adrenal medulla.
(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethylammonium Chloride ; 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester ; Acetylcholine ; Adrenal Glands ; Adrenal Medulla* ; Animals ; Calcium Channels, N-Type ; Catecholamines ; Chromaffin Cells ; Cytoplasm ; Dimethylphenylpiperazinium Iodide ; Membranes ; omega-Conotoxin GVIA ; Rats* ; Veins