Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027819 (neuroblastoma)
 27,800 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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. Batrachotoxin was both the most potent (K0.5, 0.49 microM) and most effective activator of specific 22Na+ uptake. Veratridine (K0.5, 34.5 microM) and aconitine (K0.5, 19.6 microM) produced maximal stimulations of 22Na+ uptake that were 73% and 46%, respectively, of that produced by batrachotoxin. Activation of 22Na+ uptake by veratridine was completely inhibited by tetrodotoxin (I50, 6 nM ), a specific blocker of nerve membrane sodium channels. 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.
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PMID:Mouse brain synaptosomal sodium channels: activation by aconitine, batrachotoxin, and veratridine, and inhibition by tetrodotoxin. 614 26

Anthopleurin A, a polypeptide toxin from the Pacific sea anemone Anthopleura xanthogrammica, enhances persistent activation of voltage-sensitive sodium channels by the alkaloid toxins veratridine and batrachotoxin with K0.5 = 20 nM. This effect is inhibited by depolarization. There is a close correlation between enhancement of sodium channel activation and block of [125I]scorpion toxin binding by unlabeled scorpion toxin, sea anemone toxin II from Anemonia sulcata, and Anthopleurin A, indicating that these three polypeptide toxins interact with a common receptor site in modifying sodium channel function. Photo-activable derivatives of scorpion toxin label a single Mr approximately 250,000 polypeptide chain at the polypeptide toxin receptor site. Labeling is blocked by unlabeled scorpion toxin or depolarization and is not observed in variant neuroblastoma clones, which lack sodium channels. These results identify a protein component of the polypeptide toxin receptor site of voltage-sensitive sodium channels.
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PMID:Interaction of polypeptide neurotoxins with a receptor site associated with voltage-sensitive sodium channels. 626 Oct 42

The use of sea anemone toxin, veratridine and scorpion toxin which specifically interact with the gating system of the sodium channel and maintain the channel in an open conformation has permitted a study of the mechanism of transport of monovalent cations through the selectivity filter of this channel. The initial rate of 22Na+ influx through the tetrodotoxin-sensitive Na+ channels of excitable cells is dependent upon the external concentrations of Na+ and Na+-substitutes with the following properties. (a) It is saturable at high Na+ concentrations and increases with the external Na+ concentration in a cooperative manner (nH = 1.6). (b) At low external Na+ concentrations (1 mM), it is activated and then inhibited by increasing external concentrations of monovalent cations such as Li+, guanidinium, hydrazinium, hydroxylamine and K+. The activating effect of these cations disappears at higher external Na+ concentrations (10 mM). The experimental data are consistent with a model involving at least two allosteric cation-binding sites per Na+ channel. The binding of monovalent cations to Na+ sites is characterized by a high positive homotropic cooperativity. Most of the work describes the properties of the Na+ channel in neuroblastoma cells. The mechanism has also been shown to be valid for excitable cells of other types and origins.
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PMID:Properties of the interaction of the sodium channel with permeant monovalent cations. 628 Oct

Sodium channels in cultured neural cells were localized by light microscopic autoradiography of specifically bound 125I-scorpion toxin. Ninety percent of the cell-bound 125I-scorpion toxin was associated specifically with sodium channels as assessed by the blocking of autoradiographic labeling by unlabeled scorpion toxin and by depolarization. Sodium channels were distributed uniformly in the surface membrane of neurites and cell bodies of both morphologically differentiated and undifferentiated cells of clone N18 of mouse neuroblastoma C1300. Sodium channels were distributed nonuniformly in many cultured spinal cord neurons. Visual observation indicated that 37 +/- 5% of cultured spinal cord neurons had a higher sodium channel density on the initial segment of one or more neurites than on the cell body. For these neurons, the density on one neurite initial segment averaged 7.4 +/- 1.9-fold greater than on the adjacent cell body. This increased sodium channel density may be the basis of the lower threshold for action potential generation at the axon initial segment of motor neurons and some spinal interneurons in vivo.
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PMID:Localization of sodium channels in cultured neural cells. 628 1

Variant neuroblastoma cell clones were selected for resistance to the cytotoxic effects of neurotoxins that cause persistent activation of sodium channels. Three classes of variant clones were obtained: sodium channel-deficient clones, which have markedly reduced numbers of functional sodium channels; scorpion toxin-resistant clones, which have sodium channels with an altered interaction with scorpion toxin; and parental-type clones, which have functional sodium channels similar to the ones from N18 cells but have other heritable alterations that confer toxin resistance. The frequency of conversion to all three variant phenotypes was enhanced by treatment with the missense mutagen N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), suggesting that all three variant phenotypes are the result of mutational events. Incorporation of [35S]methionine into the alpha-subunit of the sodium channel (Mr = 270,000; pI = 5.8 +/- 0.2) was studied in normal and variant clones by affinity chromatography on wheat germ agglutinin/Sepharose followed by analysis of labeled polypeptides by 1- and 2-dimensional gel electrophoresis. Sodium channel-deficient clones do not synthesize the alpha-subunit of the sodium channel, suggesting that mutations in these clones block expression of the gene for this protein subunit. The scorpion toxin-resistant clone LV10 synthesizes an alpha-subunit which has a molecular weight and pI similar to those of the parental clones within the resolution of the methods used.
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PMID:Characterization of variant neuroblastoma clones with missing or altered sodium channels. 628 70

Experimental conditions were established under which tunicamycin inhibits glycosylation by 80-90% but reduces protein biosynthesis by only 10-20% in cultured neuroblastoma cells. Growth in the presence of tunicamycin (1 micrograms/ml) reduces the number of sodium channels, as measured by high affinity saxitoxin (STX) binding to 20-28% of control values over a 60-h period without affect on the KD for STX. Neurotoxin-activated 22Na+ influx mediated by the sodium channel was similarly reduced without affect on the KD for batrachotoxin. Comparison of STX binding by intact cells or homogenates showed that tunicamycin reduces cell surface STX receptors without accumulation of an intracellular pool of binding sites. Tunicamycin caused a similar reduction in cell surface STX receptors in the presence of the lysosomal inhibitor chloroquine, suggesting that its action is not entirely due to acceleration of sodium channel degradation. The action of tunicamycin is at least partially reversible. After washout, STX receptors appear at an initial rate of approximately 1900/cell/h. Protein synthesis is required for the appearance of new sodium channels. After inhibition of sodium channel biosynthesis by either cycloheximide or tunicamycin, the number of high affinity STX receptor sites is reduced with a half-time of 26 h. Thus, at steady state, neuroblastoma cells which contain 50,000 +/- 15,000 STX receptors degrade and replace 1330 +/- 400 STX receptor sites/h. Our results show that glycosylation is an essential process in the maintenance of the normal steady state of biosynthesis and degradation of sodium channels.
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PMID:Glycosylation is required for maintenance of functional sodium channels in neuroblastoma cells. 630 Jan 16

The effect of cycloheximide (an inhibitor of protein synthesis) on the ionic currents through sodium and potassium channels was investigated in dialysed voltage-clamped N18 A-1 neuroblastoma cells. The cycloheximide concentration needed for half-inhibition of sodium peak conductance was about 0.5 micrograms/ml for 24 h of incubation. Half-inhibition time of the sodium peak conductance in cells incubated with 15.0 micrograms/ml of cycloheximide was about 9 h. Sodium against potassium ion selectivity, the activation and inactivation parameters were shown to be not affected by cycloheximide. Potassium conductance in similarly treated cells exhibited no consistent changes. The main conclusion is that the decay in peak sodium conductance is caused by diminishing the sodium channel density in the membrane (from 25 to 2.2 channels per micron2). The inhibition effect was evidently mediated by block of protein synthesis and was not the result of direct drug-channel interaction. The half-decay time of sodium peak conductance is interpreted as a possible life-time characteristic of sodium channels in the neuroblastoma cell membrane.
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PMID:Effect of cycloheximide on ionic channels in neuroblastoma cell membrane. 631 70

Single sodium channel currents were studied in mouse neuroblastoma cells. Channel conductance (gamma) was 11.6 +/- 3.4 pS at 6-8 degrees C. Unitary current amplitudes and channel activity increased with increasing temperature. The Arrhenius plot of the conductance was linear between 5 and 35 degrees C with an activation enthalpy of 27.1 kJ/mole (Q10 = 1.28). Amplitude distributions were fitted by the sum of two Gaussian functions indicating the presence of two different single channel amplitudes: smaller i1 and larger i2. The relative probability of appearance of i1, which has a shorter mean open time, was higher during the early phase of depolarization (t less than 16 ms). The open time histograms, inactivating phase of macroscopic currents and delay time histograms were fitted by the sum of two exponentials. The distinct kinetic and steady-state parameters reflect two open states of sodium channels.
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PMID:Single Na channels in mouse neuroblastoma cell membrane. Indications for two open states. 632 86

The inhibitory action of a number of clinically effective anticonvulsants on neurotoxin-activated sodium channels in cultured neuroblastoma cells and rat brain synaptosomes has been examined. Diphenylhydantoin (KI = 35 microM) and carbamazepine (KI = 41 microM) inhibited batrachotoxin-activated 22Na+ influx in N18 cells. Similarly, batrachotoxin-activated 22Na+ influx in rat brain synaptosomes was also inhibited by diphenylhydantoin (KI = 38 microM) and carbamazepine (KI = 22 microM). Comparison of KI values with mean brain levels of these drugs achieved during prevention of electroshock seizures indicates that diphenylhydantoin and carbamazepine occupy 35% and 50%, respectively, of their receptor sites associated with sodium channels at mean therapeutic concentrations. Diazepam (KI = 51 to 63 microM) and phenobarbital (KI = 1.2 to 1.3 mM) inhibited batrachotoxin-activated 22Na+ flux in N18 cells and synaptosomes at concentrations in excess of mean therapeutic central nervous system levels. Carbamazepine, like diphenylhydantoin, acts as a competitive inhibitor of sodium channel activation by the full agonist batrachotoxin, but produces mixed inhibition of veratridine-activated channels. This finding is consistent with the conclusion that both carbamazepine and diphenylhydantoin act as allosteric inhibitors of neurotoxin-activated sodium channels. The dose-response relationships for carbamazepine and diphenylhydantoin inhibition of 22Na+ flux in N18 cells are shifted 1.5-fold to higher concentrations when 22Na+ flux measurements are made in the presence of physiological concentrations of sodium and calcium ions. These results suggest that anticonvulsant inhibition of neurotoxin-activated 22Na+ flux in our standard ion flux media, containing low concentrations of Na+ and no Ca2+, is likely to reflect an effect of these agents expected in vivo. The results of this study provide further evidence to support the hypothesis that diphenylhydantoin and carbamazepine, both of which possess similar therapeutic profiles in the treatment of grand mal and partial seizures, may exert their pharmacological effects by occupancy of receptor sites associated with the activation of voltage-sensitive sodium channels in the central nervous system.
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PMID:Inhibition of voltage-sensitive sodium channels in neuroblastoma cells and synaptosomes by the anticonvulsant drugs diphenylhydantoin and carbamazepine. 632 45

The mechanisms by which external Ca ions block sodium channels were studied by a gigaohm seal patch clamp method using membranes excised from N1E-115 neuroblastoma cells. Tetramethrin was used to prolong the open time of single channels so that the current-voltage relationship could be readily determined over a wide range of membrane potentials. Comparable experiments were performed in the absence of tetramethrin. Increasing external Ca ions from 0.18 to 9.0 mM reduced the single channel conductance without causing flickering. From the dose-response relation the dissociation constant for Ca block at 0 mV was estimated to be 32.4 +/- 1.05 mM. The block was intensified by hyperpolarization. The voltage dependence indicates that Ca ions bind to sodium channels at a site located 37 +/- 2% of the electrical distance from the outside. The current increased with increasing external Na concentrations but showed a saturation; the concentration for half-maximal saturation was estimated to be 185 mM at -50 mV and 204 mM at 0 mV. A model consisting of a one-ion pore with four barriers and three wells can account for the observations that deviate from the independence principle, namely, the saturation of current, block by Ca ions, and rectification in current-voltage relationship. The results suggest that the Ca-induced decrease of the macroscopic sodium current results from a reduced single sodium channel conductance.
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PMID:Voltage-dependent calcium block of normal and tetramethrin-modified single sodium channels. 632 13


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