Pharmacologic properties of voltage-sensitive sodium channels in chick muscle fibers developing in vitro

Mad honey intoxication: A systematic review on the 1199 cases

Mad honey, produced by honeybees from the nectars of Rhododendron genus (R. ponticum and R. luteum) flowers, is widely used in indigenous medicine, especially in the treatment of hypertension and sexual dysfunction. However, the consumption of this honey can result in intoxication soon after. The diagnosis of honey poisoning and a full understanding of its treatment is important for both effective and immediate treatment, and also for the prevention of unnecessary costs. Upon the evaluation of approximately 34 years of case reports between 1981 and 2014, it was found that the cases of poisoning were more frequently reported in males (75.17%) and between the ages 41 to 65. The most common complaints related to honey poisoning were dizziness, nausea, presyncope and the ECG findings were: sinus bradycardia (79.58%), complete atrioventricular block (45.83%), atrioventricular block (30.91%), ST-segment elevation (22.63%), and nodal rhythm (11.27%), As a result of the evaluation of 1199 cases, it was found that no deaths were reported. The patients were most frequently treated with 0.5 mg atropine (37.79%), 1 mg atropine (49.73%), salin (iv fluid) (65.35%), and generally the patients were discharged within 24 h after recovery.

Evolutionary history of a complex adaptation: tetrodotoxin resistance in salamanders

Understanding the processes that generate novel adaptive phenotypes is central to evolutionary biology. We used comparative analyses to reveal the history of tetrodotoxin (TTX) resistance in TTX-bearing salamanders. Resistance to TTX is a critical component of the ability to use TTX defensively but the origin of the TTX-bearing phenotype is unclear. Skeletal muscle of TTX-bearing salamanders (modern newts, family: Salamandridae) is unaffected by TTX at doses far in excess of those that block action potentials in muscle and nerve of other vertebrates. Skeletal muscle of non-TTX-bearing salamandrids is also resistant to TTX but at lower levels. Skeletal muscle TTX resistance in the Salamandridae results from the expression of TTX-resistant variants of the voltage-gated sodium channel NaV 1.4 (SCN4a). We identified four substitutions in the coding region of salSCN4a that are likely responsible for the TTX resistance measured in TTX-bearing salamanders and variation at one of these sites likely explains variation in TTX resistance among other lineages. Our results suggest that exaptation has played a role in the evolution of the TTX-bearing phenotype and provide empirical evidence that complex physiological adaptations can arise through the accumulation of beneficial mutations in the coding region of conserved proteins.

Cultured myotubes from skeletal muscle of adult rats. Characterization and action of Anemonia sulcata toxin II

Mononucleated myogenic cells (satellite cells) were isolated from skeletal muscle of adult rats and grown in culture. These cells replicated and, beginning with the 6th day in culture, they fused and differentiated into multinucleated myotubes, which accumulated creatine kinase and developed cross striation and spontaneous contractions. The differentiation of the excitable membrane and the action of sea anemone toxin ATX II were investigated with microelectrode techniques. Mature myotubes reached a stable membrane potential of -47.3 mV (+/- 6.5 mV) with the 11th day in culture. Action potentials could be generated in all myotubes. During maturation they became faster (increasing rate of rise) and shorter in duration. In spontaneously contracting myotubes spontaneous action potentials were recorded, which were often associated with subthreshold oscillations of membrane potential. ATX II reduced the membrane potential and prolonged the action potential duration with the lowest effective concentrations being 1 nmol/l and 0.5 nmol/l, respectively. Furthermore, ATX II induced electrical activity in quiescent myotubes. After fusion the development of the membrane electrical properties of satellite cell derived muscle cells followed essentially the same pattern as in primary cultures of embryonic myotubes. Electrophysiologically and with respect to their sensitivity to ATX II the mature myotubes resemble denervated muscle fibres.

Acetylcholine receptors and sodium channels in denervated and botulinum-toxin-treated adult rat muscle

1. The number of acetylcholine (ACh) receptors and Na channels was measured in adult rat hind-limb muscles after denervation or injection of botulinum toxin type A (BoTX), using specific binding of radiolabelled neurotoxins. 2. Denervation by sciatic nerve section increased the number of [125I]iodo-alpha-bungarotoxin ([125I]BTX) binding sites from low, unmeasurable levels to 39 +/- 3 fmol of toxin bound per milligram muscle protein at 21 days. 3. Subcutaneous injection of BoTX produced complete neuromuscular blockade for 11-14 days over which time the number of [125I]BTX binding sites increased with the same time course and to the same extent as following denervation. 4. Neither denervation nor BoTX treatment significantly altered the number of tritiated saxitoxin ([3H]STX) binding sites from normal values of 7.8 fmol/mg muscle weight or 57 +/- 3 fmol/mg homogenate protein. This may, however, correspond to a lower density of [3H]STX sites in the muscle membrane. 5. It was concluded that neuromuscular blockade with BoTX is equivalent to denervation in its effects on synthesis of ACh receptors. Numbers of Na channels are more stable than ACh receptors but may also be modulated by neuromuscular activity.

High-affinity binding of alpha-scorpion toxin: a neuronal property

alpha-Scorpion toxin binding to its receptor--one component of the voltage-sensitive sodium channel--was studied in an attempt to define its phenotypic specificity. To this end we investigated the ability of neuronal, glial myogenic and fibroblastic cell lines to bind alpha-toxin II, purified from venom of the scorpion Androctonus australis Hector. A single class of saturable high-affinity (Kd congruent to 1 nM) binding sites, was present only in cell lines exhibiting some of the characteristics of normal neuronal cells, such as the N18, NIE-115, NS20, BN10-10, NG108-15 and T28 cell lines. NIA-103, which is an electrically non-excitable neuronal cell, gave negative results. In glial (G26-20, TR6B, C6) myogenic (T984) or fibroblastic (L) cell lines, we were unable to detect high-affinity binding sites for alpha-scorpion toxin. Primary cultures of rat skeletal muscle cells were also negative. Thus specific binding in the nanomolar range seems to be selectively associated with the neuronal phenotype. alpha-Scorpion toxin binding was tested before and after induction of neurites: in N18, NIE-115, NS20 cell lines, the differentiation brought on an increase in the number of binding sites but had little effect on the dissociation constant; in the hybrids NG108-15 and T28 high affinity saturable binding sites were detectable after but not prior to morphological differentiation.

Inhibition of contraction of cultured muscle fibers results in increased turnover of myofibrillar proteins but not of intermediate-filament proteins

Muscle fibers are maintained in culture in a fully contractile state and are relaxed by the addition of 10(-7) M tetrodotoxin (TTX). This toxin binds to muscle membrane Na+- channels, abolishes spontaneous contractions and causes failure of the fiber to accumulate myosin heavy chains. These effects are reversible on removal of TTX. Synthesis and accumulation kinetics have been obtained for myofibrillar and for cytoplasmic filament proteins in normal, active muscle and in TTX-relaxed muscle fibers in culture. In relaxed fibers the synthesis of most proteins remained normal or slightly elevated. However, the accumulation of all myofibrillar proteins examined was markedly inhibited in TTX-treated cultures, whereas the accumulation of cytoplasmic filament proteins was normal or slightly elevated. Myofibrillar proteins examined were alpha-actin, troponin-C, myosin fast light chain 1, myosin fast light chain 2, alpha, beta-tropomyosins and the phosphorylated forms of tropomyosin and fast light chain 2. Cytoplasmic filament proteins studied were vimentin, alpha, beta-desmin and beta, alpha-actin. We also examined the synthesis and accumulation of six unidentified muscle-specific proteins and nine unidentified nonmuscle-specific proteins. Most of these proteins showed a normal accumulation pattern in TTX-relaxed fibers. We concluded that muscle fibers made inactive by TTX display an increased instability of all myofibrillar proteins while cytoplasmic filament proteins and cytoplasmic proteins in general are relatively unaffected. We suggest that TTX interferes, in a manner as yet unidentified, with assembly and normal stability of myofibrils. Decreased assembly and/or increased instability of myofibrils would lead to increased rates of myofibrillar protein degradation.

Potentiation by crotamine of the depolarizing effects of batrachotoxin, protoveratrine A and grayanotoxin I on the rat diaphragm

The interactions between crotamine and tetrodotoxin and group II sodium channel toxins, including batrachotoxin, protoveratrine A and grayanotoxin I, were studied on the rat diaphragm muscle. When the diaphragm was pretreated with 0.1 micrograms crotamine/ml for 45 min (a condition known to depolarize the muscle by less than 3 mV, which is only 20% of the maximal depolarization induced by a saturating concentration of crotamine), the rate of depolarization by group II toxins was markedly enhanced and the time to reach the steady state depolarization was greatly shortened. The maximal depolarizations induced by each of the group II toxins, however, were not increased. Pretreatment with saturating concentrations of crotamine also caused no change of the steady state depolarization induced by batrachotoxin or grayanotoxin I. Moreover, pretreatment of the diaphragm with a high concentration of grayanotoxin I, whose effect is reversible, did not impede the depolarizing effect of crotamine. Tetrodotoxin restored the membrane potential, depolarized by crotamine, with 50% restoration at a concentration of 16 ng/ml, no matter whether a high (20 micrograms/ml) or a low (2 micrograms/ml) concentration of crotamine were used. The above results indicate that there is no competition between crotamine and group II toxins or between crotamine and tetrodotoxin. However, crotamine may affect the binding of group II toxins allosterically, increasing their affinity although the intrinsic activity may not be changed.

Tunicamycin inhibits the expression of surface Na+ channels in cultured muscle cells

We have investigated the effect of tunicamycin (TM), an inhibitor of protein glycosylation, on surface Na+ channels in cultured chick skeletal muscle cells. The expression of Na+ channels, estimated by the measurement of batrachotoxin (BTX)-activated 22Na+ uptake, was found to be significantly diminished after exposure of muscle cells to TM. This effect is partially reversed by the protease inhibitor leupeptin and is associated with a markedly enhanced rate of disappearance of Na+ channels from the surface of TM-treated cells. Our findings suggest that protein glycosylation contributes to the metabolic stability of voltage-sensitive Na+ channels.

Neurotoxins as probes in the study of neuronal development

We have investigated the expression of surface membrane binding sites for tetanus toxin and alpha-scorpion toxin (AaHII) on cells of the in vivo developing mouse nervous system. There is a close temporal correlation in the pattern of emergence and accumulation of tetanus toxin binding cells (TBC) and that of post-mitotic neurons. In different nervous system areas, the fluctuations in relative TBC abundance reflect regional changes in the dynamics of neuronal subpopulations. The results indicate that the acquisition of membrane tetanus toxin binding sites may represent one of the earliest detectable characteristics of nascent neurons. The Na+ channel-associated scorpion toxin become detectable in fetal mouse brain two days after the appearance of TBC. Their density increases with fetal age without change in receptor properties. At all stages, scorpion toxin binds to a single class of noninteracting sites with a KD = 0.1 - 0.5 nM. The affinity of binding is voltage-dependent. Studies on brain cells and various cell lines grown in vitro suggest a selective association of the high affinity scorpion toxin receptors with neuronal phenotype. In culture, as in vivo, there is a time dependent increase in receptor density. These results indicate that both tetanus toxin and scorpion toxin can be used as qualitative markers of neuronal differentiation; moreover, estimates of the density of scorpion toxin binding sites provide a quantitative index of neuronal maturation.

Regulation of myosin accumulation by muscle activity in cell culture

Tetrodotoxin (TTX), at concentrations that do not interfere with normal myogenesis or with myosin synthesis, causes of cultured muscle fibres to accumulate myosin heavy chain peptides. This effect is now shown to be reversible. On removal of TTX, muscle fibres begin to reaccumulate myosin heavy chains and it appears that the myosin heavy chains display a 230% increase in stability when cells are shifted from TTX to a normal medium without TTX. Total protein stability or turnover is not affected by TTX. The ability of TTX to induce failure of accumulation of myosin heavy-chain in cultured muscle fibres does not extend to cultured chick fibroblasts. TTX also does not perturb normal uptake of [3H] leucine during a 1 h pulse and the leucine-specific activity within TTX-treated cells is essentially equivalent to that within normal cells. Finally, limited proteolysis of myosin heavy chain isolated from TTX-treated and normal muscle fibres and display of cleavage products on SDS-polyacrylamide gels does not reveal any significant difference between the two myosins. We conclude that failure of TTX muscle to accumulate myosin heavy chain is not related to impaired synthesis, to changes in myosin heavy-chain primary structure, or to overall changes in muscle fibre proteolytic activity. We speculate that the increase in degradation and resulting failure to accumulate myosin heavy chain in TTX cells is related to an inability of TTX-related muscle fibres to assemble newly synthesized fibrillar proteins into structures such as filaments or fibrils. Failure of assembly would lead to increased exposure to base-line levels of muscle proteolysis and to the observed lack of accumulation of myosin heavy chain.