Assessing the neurotoxic effects of palytoxin and ouabain, both Na⁺/K⁺-ATPase inhibitors, on the myelinated sciatic nerve fibres of the mouse: an ex vivo electrophysiological study.
Palytoxin (PlTX) is a marine toxin originally isolated from the zoantharians of the genus Palythoa. It is considered to be one of the most lethal marine toxins that block the Na⁺/K⁺-ATPase. This study was designed to investigate the acute effects of PlTX and ouabain, also an Na⁺/K⁺-ATPase blocker, on the mammalian peripheral nervous system using an ex vivo electrophysiological preparation: the isolated mouse sciatic nerve. Amplitude of the evoked nerve compound action potential (nCAP) was used to measure the proper functioning of the sciatic nerve fibres. The half-vitality time of the nerve fibres (the time required to inhibit the nCAP to 50% of its initial value: IT₅₀) incubated in normal saline was 24.5 ± 0.40 h (n = 5). Nerves incubated continuously in 50.0, 10.0, 1.0, 0.5, 0.250 and 0.125 nM of PlTX had an IT₅₀ of 0.06 ± 0.00, 0.51 ± 0.00, 2.1 ± 0.10, 8.9 ± 0.30, 15.1 ± 0.30 h, and 19.5 ± 0.20 h, respectively (n = 5, 3, 4, 4, 10). PlTX was extremely toxic to the sciatic nerve fibres, with a minimum effective concentration (mEC) of 0.125 nM (n = 5) and inhibitory concentration to 50% (IC₅₀) of 0.32 ± 0.08 nM (incubation time 24 h). Ouabain was far less toxic, with a mEC of 250.0 μM (n = 5) and IC₅₀ of 370.0 ± 18.00 μM (incubation 24.5 h). Finally, when the two compounds were combined--e.g. pre-incubation of the nerve fibre in 250.0 μM ouabain for 1 h and then exposure to 1.0 nM PlTX--ouabain offered minor a neuroprotection of 9.1-17.6% against PlTX-induced neurotoxicity. Higher concentrations of ouabain (500.0 μM) offered no protection. The mouse sciatic nerve preparation is a simple and low-cost bioassay that can be used to assess and quantify the neurotoxic effects of standard PlTX or PlTX-like compounds, since it appears to have the same sensitivity as the haemolysis of erythrocytes assay--the standard ex vivo test for PlTX toxicity.
Laboratory of Animal Physiology, Department of Zoology, School of Biology, Aristotle University of Thessaloniki, University Campus, Thessaloniki 54124, Greece.
Alexia
A
Kagiava
Katerina
K
Aligizaki
Panagiota
P
Katikou
Georgios
G
Nikolaidis
George
G
Theophilidis
D000178:Acrylamides / Q000633:toxicity*; D000818:Animals; D037421:Anthozoa / Q000737:chemistry; D001681:Biological Assay / Q000379:methods; D003064:Cnidarian Venoms; D055724:Electrophysiological Phenomena; D005071:Evoked Potentials / Q000187:drug effects; D066298:In Vitro Techniques; D020128:Inhibitory Concentration 50; D008297:Male; D051379:Mice; D009413:Nerve Fibers, Myelinated / Q000187:drug effects; D020258:Neurotoxicity Syndromes / Q000473:pathology; D010042:Ouabain / Q000633:toxicity*; D012584:Sciatic Nerve / Q000187:drug effects* / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000095702:Polyether Toxins
D000178:Acrylamides; D003064:Cnidarian Venoms; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; C010272:palytoxin; D000095702:Polyether Toxins