Effects of BmK AS on Nav1.2 expressed in Xenopus laevis oocytes

Scorpion toxin peptide action at the ion channel subunit level

This review categorizes functionally validated actions of defined scorpion toxin (SCTX) neuropeptides across ion channel subclasses, highlighting key trends in this rapidly evolving field. Scorpion envenomation is a common event in many tropical and subtropical countries, with neuropharmacological actions, particularly autonomic nervous system modulation, causing significant mortality. The primary active agents within scorpion venoms are a diverse group of small neuropeptides that elicit specific potent actions across a wide range of ion channel classes. The identification and functional characterisation of these SCTX peptides has tremendous potential for development of novel pharmaceuticals that advance knowledge of ion channels and establish lead compounds for treatment of excitable tissue disorders. This review delineates the unique specificities of 320 individual SCTX peptides that collectively act on 41 ion channel subclasses. Thus the SCTX research field has significant translational implications for pathophysiology spanning neurotransmission, neurohumoral signalling, sensori-motor systems and excitation-contraction coupling. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'

Pharmacological kinetics of BmK AS, a sodium channel site 4-specific modulator on Nav1.3

OBJECTIVE

In this study, the pharmacological kinetics of Buthus martensi Karsch (BmK) AS, a specific modulator of voltage-gated sodium channel site 4, was investigated on Na(v)1.3 expressed in Xenopus oocytes.

METHODS

Two-electrode voltage clamp was used to record the whole-cell sodium current.

RESULTS

The peak currents of Na(v)1.3 were depressed by BmK AS over a wide range of concentrations (10, 100, and 500 nmol/L). Most remarkably, BmK AS at 100 nmol/L hyperpolarized the voltage-dependence and increased the voltage-sensitivity of steady-state activation/inactivation. In addition, BmK AS was capable of hyperpolarizing not only the fast inactivation but also the slow inactivation, with a greater preference for the latter. Moreover, BmK AS accelerated the time constant and increased the ratio of recovery in Na(v)1.3 at all concentrations.

CONCLUSION

This study provides direct evidence that BmK AS facilitates steady-state activation and inhibits slow inactivation by stabilizing both the closed and open states of the Na(v)1.3 channel, which might result from an integrative binding to two receptor sites on the voltage-gated sodium channels. These results may shed light on therapeutics against Na(v)1.3-targeted pathology.

PKA phosphorylation reshapes the pharmacological kinetics of BmK AS, a unique site-4 sodium channel-specific modulator

Although modulation of the activity of voltage-gated sodium channels (VGSCs) by protein kinase A (PKA) phosphorylation has been investigated in multiple preparations, the pharmacological sensitivity of VGSCs to scorpion toxins after PKA phosphorylation has rarely been approached. In this study, the effects of BmK AS, a sodium channel-specific modulator from Chinese scorpion Buthus martensi Karsch, on the voltage-dependent activation and inactivation of Nav1.2 were examined before and after PKA activation. After PKA phosphorylation, the pattern of dose-dependent modulation of BmK AS, on both Nav1.2α and Nav1.2 (α + β1) was reshaped. Meanwhile, the shifts in voltage-dependency of activation and inactivation induced by BmK AS were attenuated. The results suggested that PKA might play a role in different patterns how β-like toxins such as BmK AS modulate gating properties and peak currents of VGSCs.

Mining the virgin land of neurotoxicology: a novel paradigm of neurotoxic peptides action on glycosylated voltage-gated sodium channels

Voltage-gated sodium channels (VGSCs) are important membrane protein carrying on the molecular basis for action potentials (AP) in neuronal firings. Even though the structure-function studies were the most pursued spots, the posttranslation modification processes, such as glycosylation, phosphorylation, and alternative splicing associating with channel functions captured less eyesights. The accumulative research suggested an interaction between the sialic acids chains and ion-permeable pores, giving rise to subtle but significant impacts on channel gating. Sodium channel-specific neurotoxic toxins, a family of long-chain polypeptides originated from venomous animals, are found to potentially share the binding sites adjacent to glycosylated region on VGSCs. Thus, an interaction between toxin and glycosylated VGSC might hopefully join the campaign to approach the role of glycosylation in modulating VGSCs-involved neuronal network activity. This paper will cover the state-of-the-art advances of researches on glycosylation-mediated VGSCs function and the possible underlying mechanisms of interactions between toxin and glycosylated VGSCs, which may therefore, fulfill the knowledge in identifying the pharmacological targets and therapeutic values of VGSCs.

Anticonvulsant activity of BmK AS, a sodium channel site 4-specific modulator

The anticonvulsant activity of BmK AS, a sodium channel site 4-selective modulator purified from scorpion venom (Buthus martensi Karsch), was investigated in unanesthetized rats with acute pentylenetetrazole (PTZ)- and pilocarpine-induced seizures. Rats were microinjected in the CA1 region with either saline or BmK AS, followed by epileptogenic doses of PTZ or pilocarpine 30 minutes later. The anticonvulsant efficacy of BmK AS in PTZ- or pilocarpine-evoked seizure-like behavior and cortical epileptiform EEG activity was assessed. Intrahippocampal injections of BmK AS (0.05-1 μg in 1 μL) produced dose-dependent anticonvulsant activity in the PTZ model, suppressing seizure-associated behavior and reducing both the number and duration of high-amplitude, high-frequency discharges (HAFDs) on the EEG. In contrast, BmK AS did not affect the epileptiform EEG in the pilocarpine model over the same dose range, although it did increase the latency to status epilepticus onset and slightly, but significantly, reduced the seizure score. In summary, our results demonstrate that the sodium channel site 4-selective modulator BmK AS is an effective inhibitor of PTZ- but not pilocarpine-induced acute seizures. These results indicate that BmK AS may serve as a novel probe in exploring the role of different sodium channel subtypes in an epileptogenic setting and as a potential lead in developing antiepileptic drugs specifically for the therapy of sodium channel site 4-related epilepsy.