FIGURE 2. Nerve response of toxin-free, individual clams to STX in vitro.
From the following article:
Sodium channel mutation leading to saxitoxin resistance in clams increases risk of PSP
V. Monica Bricelj, Laurie Connell, Keiichi Konoki, Scott P. MacQuarrie, Todd Scheuer, William A. Catterall and Vera L. Trainer
Nature 434, 763-767(7 April 2005)
doi:10.1038/nature03415
a, Percentage decrease in the compound action potential in isolated nerve preparations exposed to increasing STX concentrations relative to the pre-exposure condition. Values are amplitudes of the action potential of three representative sensitive (open circles) and three resistant (filled circles) clams (means 
s.e.m.). The response measured when the reduction was maximized (
5 min except for the 100% block, which occurs within seconds). b, Percentage of clams tested from each population exhibiting full action potential block in relation to STX concentration (the maximum tested was 334 
M; n = 11 BF clams (filled columns) and 13 LE clams (open columns)).
