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

摘要

Palytoxin (PITX) 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 PITX 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). PITX 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 mu M (n = 5) and IC50 of 370.0 +/- 18.00 mu M (incubation 24.5 h). Finally, when the two compounds were combined - e.g. pre-incubation of the nerve fibre in 250.0 mu M ouabain for 1 h and then exposure to 1.0 nM PITX - ouabain offered minor a neuroprotection of 9.1-17.6% against PITX-induced neurotoxicity. Higher concentrations of ouabain (500.0 mu M) 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 PITX or PlTX-like compounds, since it appears to have the same sensitivity as the haemolysis of erythrocytes assay - the standard ex vivo test for PITX toxicity. (c) 2012 Elsevier Ltd. All rights reserved.