Nerve Membrane Sodium Channels Research Articles

Predators Make (Temporary) Escape from Coevolutionary Arms Race

Predators Make (Temporary) Escape from Coevolutionary Arms Race

Effect of Normal Saline and Distilled Water Used for Dilution of 4% Plain Lidocaine in Epidural Anesthesia

Background: Lidocaine blocks sodium channels in nerve membranes, which inhibits sodium influx and prevents development of an action potential. For epidural anesthesia, we usually use lidocaine diluted in normal saline or distilled water. However, diluents containing sodium ions may affect lidocaine activity. Methods: Fifty patients, ASA physical status class I or II, scheduled for elective epidural anesthesia were randomly divided into two groups. For epidural anesthesia, we used 14 ml of 2% lidocaine solution made with 7 ml of 4% lidocaine plus an equivalent of distilled water (Group DW) or normal saline (Group NS). In the right lateral decubitus position, a 19 G Arrow catheter was inserted 3 cm in the cephalad direction in the L3-4 intervertebral space. In the supine position, 3 ml of 2% lidocaine was injected as a test dose, and the remaining 11 ml of lidocaine was injected 2 minutes later. We used a pinprick test for evaluation of sensory block levels and a Bromage grade for degrees of motor block every 2 minutes during the first 30 minutes. Results: Levels of sensory block were higher in Group DW than Group NS at 12, 14 and 30 minutes. The degree of motor block was also higher in Group DW at 12 and 14 minutes. Conclusions: Diluent containing sodium ions reduces sensory and motor block compared to sodium-free solution in epidural anesthesia.

Blocking mechanisms of ketamine and its enantiomers in enzymatically demyelinated peripheral nerve as revealed by single-channel experiments.

Ketamine shows, besides its general anesthetic effect, a local anesthetic-like action that is due to blocking of peripheral nerve sodium currents. In this study, the stereoselectivity of the blocking effects of the ketamine enantiomers S(+) and R(-) was investigated in sodium and potassium channels in peripheral nerve membranes. Ion channel blockade of ketamine was investigated in enzymatically dissociated Xenopus sciatic nerves in multiple-channel and in single-channel outside-out patches. Concentration-effect curves for the Na+ peak current revealed half-maximal inhibiting concentrations (IC50) of 347 microM and 291 microM for S(+) and R(-) ketamine, respectively. The potential-dependent K+ current was less sensitive than the Na+ current with IC50 values of 982 microM and 942 microM. The most sensitive ion channel was the flickering background K+ channel, with IC50 values of 168 microM and 146 microM for S(+) and R(-) ketamine. Competition experiments suggest one binding site at the flicker K+ channel, with specific binding affinities for each of the enantiomers. For the Na+ channel, the block was weaker in acidic (pH = 6.6) than in neutral (pH = 7.4) and basic (pH = 8.2) solutions; for the flicker K+ channel, the block was weaker in acidic and stronger in basic solutions. Ketamine blockade of sodium and potassium channels in peripheral nerve membranes shows no stereoselectivity except for the flicker K+ channel, which showed a very weak stereoselectivity in favor of the R(-) form. This potential-insensitive flicker K+ channel may contribute to the resting potential. Block of this channel and subsequent depolarization of the resting membrane potential leads, besides to direct Na+ channel block, to inexcitability via Na+ channel inactivation.

Mode of action of an insecticidal peptide toxin from the venom of a weaving spider ( Diguetia canities)

A recently discovered spider toxin (DTX9.2) induced a rapid paralysis when injected into insects. In neurophysiological experiments, DTX9.2 elevated spike discharges in sensory nerves and at the neuromuscular junction, and also caused a depolarization of the membrane potential in cockroach giant axons. All these effects were reversed by treatment with the specific sodium channel blocker, tetrodotoxin. These findings suggest that DTX9.2 acts upon the voltage-dependent sodium channels of insect nerve membrane.

Mechanism of formamidine synergism of pyrethroids

The mechanism of formamidine synergism of pyrethroids in susceptible house flies and flies with target site resistance ( kdr) to pyrethroid insecticides was characterized by measurements of [ 3H]saxitoxin (STX) binding to nerve membrane sodium channels from untreated and formamidinetreated flies. Two STX binding components, one with high affinity and one with low affinity, were observed in untreated flies of each strain, and the binding constants, B max and K d , were similar for each binding component in each strain. In vivo exposure of flies to the formamidines chlordimeform and BTS 27271 appeared to change the number of STX binding components from two to one and to decrease the concentration at which saturation of STX binding occurred. Also, in vivo exposure to the formamidines changed STX binding cooperativity from negative to positive, based on Hill plot data. This change was greater with BTS 27271 than with chlordimeform and it paralleled the greater synergism of pyrethroid toxicity seen with BTS 27271. With BTS 27271 the binding affinity for STX was significantly greater in SBO than KDR flies, a result that paralleled the greater synergism seen in SBO flies. Our data suggest that formamidines are target site synergists of pyrethroids which act by modifying drug binding cooperativity in target tissue.

Das spontane und das reizevozierte EEG in der Narkose

Clear differentiation between nociception and pain, or, better, between anti-nociception and pain relief, is essential for understanding the analgesic mechanisms in anaesthesia. Nociception is a neuronal activity in the pain-mediating and pain-processing nervous system, i.e. in the peripheral axons, in the spinal short cord and in certain brain structures. The nociceptive system has been well documented by experiments, especially in animals. If this system is specifically blocked, there will be no transmission and hence no sensation of pain if we leave aside the rare and complicated instances of "psychogenic pain". Nociceptive activity is blocked or at least attenuated by anti-nociceptive drugs, such as surface anaesthetics acting in the periphery by blocking the sodium channels in the conductive nerve membrane. Opiates are another example of drugs which develop an effect on specific nociceptive neurons in the spinal cord and in the brain, thus suppressing pain transmission. An ideally effective anaesthetic should act similarly, that is by specifically and selectively suppressing nociceptive activity induced by surgery. However, general anaesthesia is based on entirely different mechanisms. It lowers the arousal level, or the vigilance of the patient. Since pain is the conscious processing of nociceptive information, attenuating the vigilance also alleviates pain; there is no pain without consciousness. Most of the centrally acting analgesics will also reduce vigilance; e.g. driving is not permitted under analgesia with opiates. Alcohol is another example, although it minimally affects the nociceptive system, it substantially lowers the vigilance, thereby alleviating pain.(ABSTRACT TRUNCATED AT 250 WORDS)

Apparent reduction in the number of nerve membrane sodium channels in the house fly in relation to metabolic resistance to insecticides

Nerve membrane sodium channels were assayed by measuring [ 3H]saxitoxin (STX) binding and its displacement by tetrodotoxin (TTX) from house fly head membrane preparations. Activity was measured in a susceptible strain and in strains with single or combinations of genes for target site resistance to pyrethroids and metabolic resistance to insecticides. The affinities ( K d values) for STX binding were similar in all strains, indicating that qualitative differences in sodium channels associated with STX binding were not involved in resistance to pyrethroid insecticides. The amount of STX binding ( B max) was the same in a susceptible strain and a strain with only target site resistance to pyrethroids, indicating that quantitative differences in sodium channels were not involved in resistance. In cotrast, the amount of STX binding was reduced in strains with metabolic resistance to insecticides. The results explain contradictions reported from several previous studies of STX binding in relation to pyrethroid resistance and suggest that the use of strains combining target site and metabolic resistance was responsible for the previous findings.

Reduction in number of nerve membrane sodium channels in pyrethroid resistant house flies

Neurotoxicity of pyrethroids, DDT, and certain steroidal alkaloids is due to modification of voltage-dependent sodium channels. Knockdown resistant ( kdr) insects are resistant to pyrethroids and DDT insecticides due to decreased nerve sensitivity to these toxins. Using nerve membrane preparations from wild-type and kdr house flies, I have characterized sodium channels by [ 3H]saxitoxin binding and acetylcholine receptors by 125I-labeled α-bungarotoxin binding. Results indicate that while acetylcholine receptor content is identical in the two strains, kdr flies contain a decreased content of sodium channels as compared to wild-type flies. As assessed by saxitoxin binding characteristics, sodium channels from wild-type and kdr flies are identical. These results suggest that a reduction in the number of voltage-dependent sodium channels is a mechanism of resistance to neurotoxins that cause persistent channel activation.

Alkaloid neurotoxins-dependent sodium transport in insect synaptic nerve-ending particles

1. 1. Sodium uptake associated with the activation of voltage-sensitive sodium channels by alkaloid activators, batrachotoxin, veratridine, and aconitine in presynaptic nerve terminals isolated from the central nervous system of cockroach ( Periplaneta americana) was investigated. 2. 2. Batrachotoxin ( K 0.5, 0.2 μM) was full agonist as for most effective activator of Na + uptake; veratridine ( K 0.5, 2.5 μM) and aconitine ( K 0.5, 7.6 μM) produced a maximal stimulation of 22Na + uptake that were 71% and 43% respectively of that produced by batrachotoxin. 3. 3. Veratridine-dependent 22Na + uptake was completely inhibited by tetrodotoxin ( I 0.5, 11 nM), a specific inhibitor of the nerve membrane sodium channels. 4. 4. The present study describes appropriate conditions for measuring neurotoxins — stimulated sodium transport in insect central nervous system synaptosomes. The data show that voltage-sensitive sodium channels as defined by specific activation by the alkaloid neurotoxins are qualitatively distinct in insect synaptosomes than those previously described for vertebrate brain synaptosomes, cultured neuronal cell, nerve membrane vesicles and neuroblastoma cells.

Activity of tralomethrin to modify the nerve membrane sodium channel

Deltamethrin is a potent type II pyrethroid insecticide which can modify sodium channel gating kinetics in nerve membranes. The actions of another type II pyrethroid tralomethrin to modify sodium channel kinetics have been ascribed to deltamethrin, to which tralomethrin is known to be converted under certain experimental conditions. The objective of this study was to determine if tralomethrin was intrinsically active in modifying the nerve membrane sodium channel, the major target site of pyrethroids. Experiments were performed using the squid giant axon under voltage-clamp conditions. In axons treated with either pyrethroid, a large sodium tail current was generated upon repolarization from a depolarized level and decayed slowly with a dual exponential time cuurse. The fast time constant for tralomethrin was 165 ± 110 msec and the slow time constant was 3793 ± 802 msec. For deltamethrin the time constants were significantly shorter, the fast time constant being 34 ± 6 msec and the slow time constant being 835 ± 282 msec. The cumulative dose-response relation of tralomethrin revealed two binding sites with apparent dissociation constants of 0.06 and 5 μ m. Deltamethrin appeared to bind to only one site with an apparent dissociation constant of 0.25 μ m. It is clear that there are large differences in the gating kinetics of the sodium channels modified by tralomethrin and deltamethrin which are incompatible with the idea that tralomethrin is active only after conversion to deltamethrin. The differences in sodium channel gating kinetics after modification by tralomethrin versus deltamethrin indicate that tralomethrin is intrinsically active in modifying the nerve membrane sodium channels.

The analgesic effect of tocainide in trigeminal neuralgia

Tocainide is a derivative of lidocaine with anti-arrhythmic action and, unlike lidocaine, can be used for oral treatment. Tocainide was alternatively with carbamazepine given to 12 patients with trigeminal neuralgia in a double-blind cross-over study for 2 weeks. The analgesic effect was estimated each day by the patients using a 0–10-point scale summarizing the frequency and severity of the attacks. The similarity in analgesic effect of the two drugs was striking. A possible analgesic mechanism could be that tocainide blocks the sodium channels in the hyperexcitable nerve membranes in the pain-producing foci in trigeminal neuralgia.

Nerve membrane sodium channels as the target site of brevetoxins at neuromuscular junctions

Actions of two structurally related toxins, T-17 and brevetoxin-B, isolated from the red-tide dinoflagellate, Ptychodiscus brevis, were studied on the giant axon of the squid and the neuromuscular junctions of the frog and rat. T-17 toxin caused a large increase in the frequency of miniature endplate potentials at nanomolar concentrations. In one typical case with a frog endplate, the frequency increased from 1.9 s-1 before application of 3.5 nM T-17 to 69.3 s-1 within 5 min after application. In the rat muscle, the mean frequency increased from 1.39 s-1 in control to 11.93 s-1 after application of 23.2 nM T-17. The increase in miniature endplate potential frequency was reversed by the addition of 1 microM tetrodotoxin, and was not observed in a solution containing elevated Mg2+ and reduced Ca2+ concentrations. External or internal application of T-17 toxin (2-5 microM) or brevetoxin-B (10-30 microM) to intact or internally perfused squid axons caused a depolarization of the membrane. This depolarization was abolished by the removal of external Na+ or by addition of tetrodotoxin to the external solution. In voltage clamped squid giant axons, exposure to T-17 toxin or brevetoxin-B increased the non-inactivating component of the tetrodotoxin-sensitive sodium current. The sodium current was activated at potentials 15 to 40 mV more negative than control. It is proposed that these toxins modify a fraction of the sodium channels to a form which opens at potentials more negative than normal and which inactivates to a lesser extent. This mechanism would predict a depolarization of the nerve membrane at the neuromuscular junction, thus explaining the increased discharge of transmitter.

Interaction of tralomethrin, tralocythrin, and related pyrethroids in Na + channels of insect and mammalian neuronal cells

The neurotoxic activity of the tetrahalogenated pyrethroids, tralomethrin and tralocythrin, which are dibromo adducts of deltamethrin and RU 24501, respectively, and RU 27218, which is a dichloro adduct of RU 24501, have been studied on two different excitable membranes using in vitro methods: insect axonal membranes and mammalian neuroblastoma cells in culture. The results show that molecules whose chrysanthemic acid chain at C 3 is saturated by halogen addition have intrinsic toxicity on the sodium channels of nerve membranes. They increase the amplitude of negative after-potential, depolarize the cockroach axonal membrane, and stabilize an open conformation of voltage-dependent Na + channels in mouse neuroblastoma cells, thereby producing a massive uptakeof Na + by the cells. All effects were observed in the absence of metabolic transformation of the compounds tested. In light of these experiments, it is concluded that tralomethrin and tralocythrin cannot be considered as propyrethroids.

Characterization of mRNA responsible for induction of functional sodium channels in Xenopus oocytes

When Xenopus laevis oocytes were microinjected with poly(A)+ mRNA isolated from adult rat brains or electric organs of Electrophorus electricus, the oocytes developed functional sodium channels. Upon application of veratrine, the microinjected oocytes exhibited transient depolarization, resulting in spontaneous repetitive spikes in some occasions, and action potentials. These responses were mediated mainly by external Na ions, prolonged by scorpion toxin, completely blocked by tetrodotoxin, and suppressed by local anesthetics. Thus the mRNA-induced sodium channels exhibited essentially all the functional properties expected for native sodium channels in nerve and muscle membranes. Rat brain mRNA was fractionated into 4 fractions by sucrose gradient centrifugation. Each fraction and various combinations of them were examined for the efficiency in inducing functional sodium channels in Xenopus oocytes. A fraction corresponding to mRNA of approximately 30S to 46S was found to contain all mRNA necessary for the expression of the channels, indicating that mRNA of smaller sizes expected to code for smaller polypeptides may not be required.

Carbofuran triggers flight motor output in pyrethroid-blocked reflex pathways of the house fly

The initiation of flight from loss of tarsal contact (flight reflex responses) and the tergotrochanteral muscle (TTM) responses evoked by brain stimulation were analyzed during carbofuran, permethrin, deltamethrin, and DDT poisoning in the house fly. Blockage of the flight reflex by LD 50 doses of permethrin or deltamethrin was rapid, but the effects of DDT on the flight reflex took hours to develop. In addition, carbofuran treatment induced spontaneous flight in blocked preparations by an action in the central nervous system. This result suggests that pyrethroid blockage of the flight reflex was due to an action on sensory nerves, since the central flight program and its associated efferent systems were functionally intact. The relevance of this finding in terms of pyrethroid knockdown is discussed. The TTM response was unaffected by permethrin or deltamethrin both early and late in the poisoning process, possibly because the evoked TTM response does not involve peripheral sensory nerves, which seem to be important sites of pyrethroid action early in poisoning. Carbofuran induced repetitive firing and blockage of the TTM response within 1 hr, but normal responses were observed late in poisoning, which is consistent with the reversibility of carbamate inhibition of acetylcholinesterase. DDT caused no change in the evoked TTM response until bursts were recorded about 15 hr after treatment; this was another example of a slowly developing DDT effect. The protracted development of various DDT actions was concordant with a hypothesis of reduced efficacy at a proposed target site, viz., the sodium channels of nerve membranes.

Mouse brain synaptosomal sodium channels: Activation by aconitine, batrachotoxin, and veratridine, and inhibition by tetrodotoxin

1. 1. Batrachotoxin, veratridine and aconitine, activators of the voltage-dependent sodium channel in excitable cell membranes, increase the rate of 22Na + uptake by mouse brain synaptosomes. 2. 2. Batrachotoxin was both the most potent ( K 0.5, 0.49 μM) and most effective activator of specific 22Na + uptake. Veratridine ( K 0.5, 34.5 μM) and aconitine ( K 0.5, 19.6 μM) produced maximal stimulations of 22Na + uptake that were 73% and 46%, respectively, of that produced by batrachotoxin. 3. 3. Activation of 22Na + uptake by veratridine was completely inhibited by tetrodotoxin ( I 50, 6 nM), a specific blocker of nerve membrane sodium channels. 4. 4. These results identify appropriate conditions for measuring sodium channel-dependent 22Na + flux in mouse brain synaptosomes. The pharmacological properties of mouse brain synaptosomal sodium channels described here are distinct from those previously described for sodium channels in rat brain synaptosomes and mouse neuroblastoma cells.

Ion selectivity of the nerve membrane sodium channel incorporated into liposomes

Tetrodotoxin-sensitive sodium channels of lobster nerve membranes were incorporated into soybean liposomes by the freeze-thaw-sonication procedure and their ionic selectivity was studied. Veratridine and grayanotoxin-I were used to activate the sodium channels and the increment of the ionic flux through them was specifically abolished by tetrodotoxin. The drug-sensitive 22Na +, 42K +, 86Rb + and 137Cs + influxes were measured. The permeability ratios calculated directly from ion fluxes showed that the channels preferably allow the passage of Na +. No anion influx ([ 32P]phosphate, [ 35S]sulfate, 36Cl) sensitive to the drugs was observed. The data reveal that the sodium channels incorporated into liposomes remain cation-selective and discriminate among different cations.

Modification of nerve membrane sodium channels by the insecticide pyrethroids

1. The synthetic pyrethroids exert potent and selective actions on nerve membrane sodium channels. (+)- trans tetramethrin and (+)- trans allethrin cause repetitive discharges to be produced in the isolated crayfish and squid giant axons in response to a single stimulus as a result of an increase in depolarizing after-potential. 2. The latter effect is due to slowing of the sodium channel kinetics which causes a prolonged sodium current following the normal peak sodium current. 3. A kinetic model is proposed to account for the action of the pyrethroids in which the pyrethroid molecule binds to the sodium channels at both closed and open states to produce a modified open state. 4. (−)- trans and (−)- cis isomers of tetramethrin are ineffective in causing the effects, but prevent the active (+)- trans and (+)- cis isomers from exerting the effects. This stereospecificity provides us with an excellent opportunity for the study of binding sites of pyrethroids and other sodium channel modulators.

Sodium channels in nerve and muscle membrane.

Nerve cells are able to transmit and store information in the form of action potentials (APs) because highly specialized membrane properties allow rapid and reversible changes in membrane 'permeability to 'specific ions. Nerve cells use metabolic work to generate concentration gradients across their membranes. Membrane permeability changes release this en­ ergy as transient changes in membrane potential, i.e. nerve impulses. Studies of excitable membranes in the last decade have focused on the molecular structures responsible for membrane permeability changes, the ion They are the most important class of membrane protein for nerve function. Different types of channels provide neuron structures with the membrane properties needed for AP propagation along axons, impulse transmission across synapses, and integrative responses of nerve cell bodies to multiple inputs. Current study of channels seeks the key to individual nerve cell properties and the more complex cell-cell interrela­ tions necessary for nervous system function. Such research has begun to provide a molecular description of nervous system function. Nervous system development and plasticity must also depend on mem­ brane properties and hence are ultimately determined by channels. Neurons undergo morphological differentiation, as well as adaptation of membrane functional properties to meet certain tasks. Control mechanisms must exist to regulate expression of excitability, to meet different physiologi­ cal needs. These mechanisms allow a neuron to (a) specify synthesis of channels with different structural characteristics, suited to particular mem­ brane functions, and (b) regulate the distribution and density of different types of channels in different portions of its membrane.

Radioactive labeling of toxin II from Anemonia sulcata

Anemone toxins are useful tools for the investigation of sodium channels in nerve membranes. For this application radioactive derivatives are necessary and are described in this report. Toxin II from Anemonia sulcata (ATX II) has been tritiated by reductive alkylation via the Schiff base formed by pyridoxal phosphate and amino groups of the peptide toxin. From the mixture of reaction products two monosubstituted toxins have been isolated by ion-exchange chromatography. The site of modification has been identified as the N-terminal amino group in the one toxin and the ϵ-amino group of lysine 35 in the other. The modified toxins prolonged action potentials similar to those of the native toxins. The threshold concentration to obtain this effect was approximately three times higher for the tritiated derivatives.