AA sequence: GVPCLCDSDGPSVRGNTLSGIIWLAGCPSGWHNCKKHGPTIGWCCKQ
Disulfide bonds: Cys4-Cys44, Cys6-Cys34, Cys27-Cys45
Length (aa): 47
Formula: C213H323N63O61S6
Molecular Weight: 4934.63 g/mol
CAS number: 60748-45-0
Source: Synthetic
Purity rate: > 95 %
ATX-II
ATX-II is a Nav1.5 activator
ATX-II was originally discovered in 1976 by extraction from the tentacles of Anemonia sulcata (Bergman et al., 1976). At that time, it was already discovered that it has activity on voltage-dependent Na+ channels from the frog Rana esculenta by slowing the rate of inactivation. Later, it was found that the purified toxin has a positive inotropic effect on isolated guinea pig atria linked to delayed inactivation of the Na+ channel (Alsen et al., 1982). ATX-II acts as a late inward Na+ current inducer in the heart that produces atrial arrhythmias, partly because it also promotes Ca2+/calmodulin-dependent protein kinase activation and concomitant Nav1.5 channel phosphorylation and further activation (Liang et al., 2016). Because late inward Na+ current is difficult to witness, but is a risk factor for the induction of cardiac arrhythmias, it is now mandatory for the FDA that all drugs to be approved should lack effect on the ATX-II-induced late inward Nav1.5 Na+ current. ATX-II is a site 3 toxin and affects domain IV voltage-sensor movement. ATX-II is a carboxylated 47 amino acid peptides with 3 disulfide bridges and of 4934.7 Da molecular weight, recently produced by Smartox Biotechnology in its synthetic form.
BULK quantities are available.
ATX-II has been tested on the human Nav1.5 channel at various concentrations at a holding potential of -90 mV and a test potential of 10 mV. Test depolarization lasted 50 ms. Appearance of a significant late Na current is visible at 1 nM and this effect is further enhanced at 10 nM ATX-II illustrating the potency of the synthetic compound of Smartox
- Jingzhaotoxin-III: Nav1.5 blocker
- Tf2: Nav1.3 activator
- OD1: Nav1.7 activator
Inhibition of the sodium inactivation of the nodal membrane by anemonia sulcate toxin
A neurotoxin (ATX-II) extracted from the tentacles of Anemonia sulcata has been found to interact with the sodium channel of the nodal membrane in myelinated nerve fibres from Rana esculenta. If externally applied at low concentration (Kd = 20 muM), it reduces considerably the rate of inactivation of the sodium conductance without affecting the activation. At such concentrations, the potassium conductance is not affected. If internally applied ATX-II does not affect the membrane conductance.
Studies on the mechanism of the positive inotropic effect of ATX II...
The basic polypeptide ATX II (MW 4,770) isolated from the sea anemone Anemonia sulcata evokes a pronounced and dose-dependent positive inotropic effect in different mammalian heart preparations. The mechanism of this effect is so far unknown. (a) Investigations on isolated guinea pig atria indicate that changes of the steady state cellular Na, K and Ca concentrations cannot account for the positive inotropic effect. (b) An increase of the surface pressure of phospholipid monolayers was observed only at cardiotoxic ATX II concentrations. However, the 45Ca binding to phosphatidylserine, as the essential Ca-binding phospholipid, was not changed even at cardiotoxic ATX II concentrations. (c) Neither the enzymatic activity nor the ouabain inhibition kinetic of an isolated Na/K-ATPase preparation was affected by ATX II. (d) In intact electrically stimulated (1 Hz) guinea pig atria the binding of [3H]ouabain increases by about 50% at a positive inotropic ATX II concentration. The results suggest that the positive inotropic effect of ATX II is not caused by an unspecific membrane damaging action or by a direct interaction with the Na/K-ATPase. The increased binding of [3H]ouabain to intact heart muscles indirectly reflects an increased pump activity of the Na/K-ATPase, which is caused by an elevated Na transient due to the electrophysiologically well-established mechanism of the ATX II action on fast Na channel, i.e., delayed inactivation of the fast Na flux. However, the exact mechanism of the ATX II induced positive inotropic effect remains unknown.
Inhibitions of late Ina and CaMKII act synergistically to prevent ATX-II-induced...
Increases in late Na(+) current (late INa) and activation of Ca(2+)/calmodulin-dependent protein kinase (CaMKII) are associated with atrial arrhythmias. CaMKII also phosphorylates Nav1.5, further increasing late INa. The combination of a CaMKII inhibitor with a late INa inhibitor may be superior to each compound alone to suppress atrial arrhythmias. Therefore, we investigated the effect of a CaMKII inhibitor in combination with a late INa inhibitor on anemone toxin II (ATX-II, a late INa enhancer)-induced atrial arrhythmias.
METHODS AND RESULTS: Rat right atrial tissue was isolated and preincubated with either the CaMKII inhibitor autocamtide-2-related inhibitory peptide (AIP), the late INa inhibitor GS458967, or both, and then exposed to ATX-II. ATX-II increased diastolic tension and caused fibrillation of isolated right atrial tissue. AIP (0.3μmol/L) and 0.1μmol/L GS458967 alone inhibited ATX-II-induced arrhythmias by 20±3% (mean±SEM, n=14) and 34±5% (n=13), respectively, whereas the two compounds in combination inhibited arrhythmias by 81±4% (n=10, p<0.05, vs either AIP or GS458967 alone or the calculated sum of individual effects of both compounds). AIP and GS458967 also attenuated the ATX-induced increase of diastolic tension. Consistent with the mechanical and electrical data, 0.3μmol/L AIP and 0.1μmol/L GS458967 each inhibited ATX-II-induced CaMKII phosphorylation by 23±3% and 32±4%, whereas the combination of both compounds inhibited CaMKII phosphorylation completely.
CONCLUSION: The effects of an enhanced late INa to induce arrhythmic activity and activation of CaMKII in atria are attenuated synergistically by inhibitors of late INa and CaMKII.