Pharmacological characterization of the voltage-dependent sodium channels of rainbow trout brain synaptosomes (original) (raw)
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Journal of Biological Chemistry, 1996
Sodium channels posses receptor sites for many neurotoxins, of which several groups were shown to inhibit sodium current inactivation. Receptor sites that bind ␣and ␣-like scorpion toxins are of particular interest since neurotoxin binding at these extracellular regions can affect the inactivation process at intramembranal segments of the channel. We examined, for the first time, the interaction of different scorpion neurotoxins, all affecting sodium current inactivation and toxic to mammals, with ␣-scorpion toxin receptor sites on both mammalian and insect sodium channels. As specific probes for rat and insect sodium channels, we used the radiolabeled ␣-scorpion toxins AaH II and Lqh␣IT, the most active ␣-toxins on mammals and insect, respectively. We demonstrate that the different scorpion toxins may be classified to several groups, according to their in vivo and in vitro activity on mammalian and insect sodium channels. Analysis of competitive binding interaction reveal that each group may occupy a distinct receptor site on sodium channels. The ␣-mammal scorpion toxins and the anti-insect Lqh␣IT bind to homologous but not identical receptor sites on both rat brain and insect sodium channels. Sea anemone toxin ATX II, previously considered to share receptor site 3 with ␣-scorpion toxins, is suggested to bind to a partially overlapping receptor site with both AaH II and Lqh␣IT. Competitive binding interactions with other scorpion toxins suggest the presence of a putative additional receptor site on sodium channels, which may bind a unique group of these scorpion toxins (Bom III and IV), active on both mammals and insects. We suggest the presence of a cluster of receptor sites for scorpion toxins that inhibit sodium current inactivation, which is very similar on insect and rat brain sodium channels, in spite of the structural and pharmacological differences between them. The sea anemone toxin ATX II is also suggested to bind within this cluster.
Several scorpion toxins have been shown to exert their neuro- toxic effects by a direct interaction with voltage-dependent sodium channels. Both classical scorpion a-toxins such as Lqh II from Leiurus quiquestratus hebraeus and a-like toxins as toxin III from the same scorpion (Lqh III) competitively interact for binding on receptor site 3 of insect sodium channels. Con- versely, Lqh III, which is highly toxic in mammalian brain, re- veals no specific binding to sodium channels of rat brain syn- aptosomes and displaces the binding of Lqh II only at high concentration. The contrast between the low-affinity interaction and the high toxicity of Lqh III indicates that Lqh III binding sites distinct from those present in synaptosomes must exist in the brain. In agreement, electrophysiological experiments per- formed on acute rat hippocampal slices revealed that Lqh III strongly affects the inactivation of voltage-gated sodium chan- nels recorded either in current or voltage clamp, wherea...
Voltage-Gated Sodium Channels Modulation by Bothutous Schach Scorpion Venom
2016
Buthotus schach is one of the dangers scorpion in Iran that belong to the Buthidae family. Toxins are existing in venom scorpion, modulate the ion channels by blocking or opening the pore of the channel or by altering the voltage gating and useful as pharmacological tools. In the present study, we investigated the effect of venom and its obtained fractions by gel filtrations on electrophysiological properties of magnocellular supraoptic of hypothalamus by using whole cell patch clamp. In our result were shown, scorpion crude venom and its fraction effect on Na gated voltage channels. A significant decrease was revealed in amplitude firing, in venom various concentration and some of the venom fraction. Also a significant increase was shown in half width and rise time 10% to 90% actions potential firing. Previous evidence was revealed change in electrophysiological properties such as amplitude and rise time 10% to 90%, related to sodium gated voltage channels. Sodium channels toxins e...
Variability among insect sodium channels revealed by selective neurotoxins
Insect Biochemistry and Molecular Biology, 1994
Binding assays with the radioiodinated depressant (LqhlTz) and excitatory (AalT) insect selective neurotoxins derived from scorpion venoms to neuronal membrane preparations derived from cockroach, fly and lepidopterous larvae coupled with the employment of sodium channel site-directed antibodies resulted in the following information. (1) The two toxins were shown to bind with high affinity to the insect neuronal preparations and revealed similar binding constants in each of the various preparations.
Animal Toxins Influence Voltage-Gated Sodium Channel Function
Handbook of Experimental Pharmacology, 2014
Voltage-gated sodium (Nav) channels are essential contributors to neuronal excitability, making them the most commonly targeted ion channel family by toxins found in animal venoms. These molecules can be used to probe the functional aspects of Nav channels on a molecular level and to explore their physiological role in normal and diseased tissues. This chapter summarizes our existing knowledge of the mechanisms by which animal toxins influence Nav channels as well as their potential application in designing therapeutic drugs.
The Journal of Neuroscience, 1999
Several scorpion toxins have been shown to exert their neurotoxic effects by a direct interaction with voltage-dependent sodium channels. Both classical scorpion ␣-toxins such as Lqh II from Leiurus quiquestratus hebraeus and ␣-like toxins as toxin III from the same scorpion (Lqh III) competitively interact for binding on receptor site 3 of insect sodium channels. Conversely, Lqh III, which is highly toxic in mammalian brain, reveals no specific binding to sodium channels of rat brain synaptosomes and displaces the binding of Lqh II only at high concentration. The contrast between the low-affinity interaction and the high toxicity of Lqh III indicates that Lqh III binding sites distinct from those present in synaptosomes must exist in the brain. In agreement, electrophysiological experiments performed on acute rat hippocampal slices revealed that Lqh III strongly affects the inactivation of voltage-gated sodium chan-nels recorded either in current or voltage clamp, whereas Lqh II had weak, or no, effects. In contrast, Lqh III had no effect on cultured embryonic chick central neurons and on sodium channels from rat brain IIA and 1 subunits reconstituted in Xenopus oocytes, whereas sea anemone toxin ATXII and Lqh II were very active. These data indicate that the ␣-like toxin Lqh III displays a surprising subtype specificity, reveals the presence of a new, distinct sodium channel insensitive to Lqh II, and highlights the differences in distribution of channel expression in the CNS. This toxin may constitute a valuable tool for the investigation of mammalian brain function.
Binding of an α scorpion toxin to insect sodium channels is not dependent on membrane potential
FEBS Letters, 1993
The insect-specific LqhaIT toxin resembles a scorpion toxins affecting mammals by its amino acid sequence and effects on sodium conductance. The present study reveals that LqhaIT does not bind to rat brain membranes and possesses in locust neuronal membranes a single class of high affinity (& = 1.06 f 0.15 nM) and low capacity (B,,,, = 0.7 f 0.19 pmol/mg protein) binding sites. The latter are: (1) distinct from binding sites of other sodium channel neurotoxins; (2) inhibited by sea anemone toxin II; (3) cooperatively interacting with veratridine; (4) not dependent on membrane potential, in contrast to the binding sites of a toxins in vertebrate systems. These data suggest the occurrence of (a) conformationalstructural differences between insect and mammal sodium channels and (b) the animal group specificity and pharmacological importance of the u scorpion toxins.
Proceedings of the National Academy of Sciences, 1980
Iodination of toxin II from the sea anemone Anemonia sulcata gives a labeled monoiododerivative that retains 80% of the original neurotoxicity. This derivative binds specifically to rat brain synaptosomes at 20 degrees C and pH 7.4 with a second-order rate constant of association ka = 4.6 x 10(4) M-1 sec-1 and a first-order rate constant of dissociation kd = 1.1 x 10(-2) sec-1. The binding occurs on the Na+ channel at a binding site distinct from that of other gating system toxins like batrachotoxin, veratridine, grayanotoxin, aconitine, and pyrethroids. The maximal binding capacity Bmax is 3.2 pmol/mg of protein (i.e., about two sea anemone toxin binding sites per tetrodotoxin binding site) and the Kd is 240 nM for the monoiododerivative and 150 nM for the native toxin. Corresponding binding parameters for the association of a 125I-labeled derivative of toxin II from the scorpion Androctonus australis Hector are Bmax = 0.3 pmol/mg of protein and Kd = 1 nM, whereas the Kd of the unm...