Analysis of Caribbean ciguatoxin-1 effects on frog myelinated axons and the neuromuscular junction.
ABSTRACT Caribbean ciguatoxin-1 (C-CTX-1) induced, after about 1h exposure, muscle membrane depolarisation and repetitive post-synaptic action potentials (APs) in frog neuromuscular preparations. This depolarising effect was also observed in a Ca(2+)-free medium with a strong enhancement of spontaneous quantal transmitter release, compared with control conditions. The ciguatoxin-induced increase in release could be accelerated when Ca(2+) was present in the extracellular medium. C-CTX-1 also enhanced nerve-evoked quantal acetylcholine (ACh) release. At normal neuromuscular junctions loaded with the fluorescent dye FM1-43, C-CTX-1 induced swelling of nerve terminals, an effect that was reversed by hyperosmotic d-mannitol. In myelinated axons, C-CTX-1 increased nodal membrane excitability, inducing spontaneous and repetitive APs. Also, the toxin enlarged the repolarising phase of APs in control and tetraethylammonium-treated axons. Overall, our data suggest that C-CTX-1 affects nerve excitability and neurotransmitter release at nerve terminals. We conclude that C-CTX-1-induced up-regulation of Na(+) channels and the inhibition of K(+) channels, at low nanomolar concentrations, produce a variety of functional dysfunctions that are in part responsible for the human muscle skeletal symptoms observed in ciguatera. All these dysfunctions seem to result from the subtle balance between ionic currents, intracellular Na(+) and Ca(2+) concentrations, and engaged second messengers.
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ABSTRACT: Ciguatoxins, mainly produced by benthic dinoflagellate Gambierdiscus species, are responsible for a complex human poisoning known as ciguatera. Previous pharmacological studies revealed that these toxins activate voltage-gated Na(+) channels. In frog nodes of Ranvier, ciguatoxins induce spontaneous and repetitive action potentials (APs) and increase axonal volume that may explain alterations of nerve functioning in intoxicated humans. The present study aimed determining the ionic mechanisms involved in Pacific ciguatoxin-1B (P-CTX-1B)-induced membrane hyperexcitability and subsequent volume increase in frog nodes of Ranvier, using electrophysiology and confocal microscopy. The results reveal that P-CTX-1B action is not dependent on external Cl(-) ions since it was not affected by substituting Cl(-) by methylsulfate ions. In contrast, substitution of external Na(+) by Li(+) ions suppressed spontaneous APs and prevented nodal swelling. This suggests that P-CTX-1B-modified Na(+) channels are not selective to Li(+) ions and/or are blocked by these ions, and that Na(+) influx through Na(+) channels opened during spontaneous APs is required for axonal swelling. The fact that the K(+) channel blocker tetraethylammonium modified, but did not suppress, spontaneous APs and greatly reduced nodal swelling induced by P-CTX-1B indicates that K(+) efflux might also be involved. This is supported by the fact that P-CTX-1B, when tested in the presence of both tetraethylammonium and the K(+) ionophore valinomycin, produced the characteristic nodal swelling. It is concluded that, during the action of P-CTX-1B, water movements responsible for axonal swelling depend on both Na(+) influx and K(+) efflux. These results pave the way for further studies regarding ciguatera treatment.Neuropharmacology 06/2014; 85:417-426. DOI:10.1016/j.neuropharm.2014.06.001 · 4.82 Impact Factor
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ABSTRACT: The prevalence of poisoning events due to harmful algal blooms (HABs) has declined during the last two decades through monitoring programs and legislation, implemented mainly for bivalves. However, new toxin vectors and emergent toxins pose a challenge to public health. Several locations on the Portuguese coast were surveyed between 2009 and 2010 for three distinct biotoxin groups [saxitoxin (PST), spirolide (SPX) and okadaic acid (OA)], in 14 benthic species of mollusks and echinoderms. Our main goals were to detect new vectors and unravel the seasonal and geographical patterns of these toxins. PSTs were analyzed by the Lawrence method, SPXs by LC-MS/MS, and OA by LC-MS/MS and UPLC-MS/MS. We report 16 new vectors for these toxins in the North Atlantic. There were differences in toxin contents among species, but no significant geographical or seasonal patterns were found. Our results suggest that legislation should be adjusted to extend the monitoring of marine toxins to a wider range of species besides edible bivalves.Marine Drugs 06/2013; 11(6):1936-60. DOI:10.3390/md11061936 · 3.51 Impact Factor
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ABSTRACT: Ciguatera is a disease transmitted, particularly by fish consumption. Fishes that come from tropical and subtropical waters where reefs and corals abound, have more probability of being contaminated with the different forms of ciguatoxin and only humans are poisoned when they consume contaminated fishes. The symptomatology appear generally in the first 24 hours, in a fast way, and they are characterized for gastrointestinal, neurological and cardiovascular symptoms. In some cases also chronic neurological, urinary and psychiatric symptoms can be presented. A possible transmission by human milk is mentioned. Epidemiological and clinical criteria are very important to do a suitable clinical impression and through instances of public health to promote the mechanisms for the definitive diagnosis of the disease by means of the microbiological exam of the species of consumed fish. The treatment is symptomatic and it requires subsequent controls for the chronic complications. The authorities of public and environmental health must look for means and methods to prevent the consumption of fishes with high risk of being contaminated. Rev.Cienc.Biomed. 2013;4(1):174-185