b1 at more negative membrane potentials (Fig. 2C). The
voltage of half-maximal activation (V1=2) shifted towards more
hyperpolarised voltages with -
12.0 mV when 5 lM BTX was
applied ðn ¼ 6Þ and with -
14.8 mV in the presence of 10 lM
BTX ðn ¼ 4Þ (Table 1). As can be seen in part IV of Fig. 2A,
Nav1.8/b1 activates at )20 mV under the influence of BTX,
whereas in control conditions the channels are still closed. As a
result of the total loss of inactivation and the leftward shift of
the activation curve, the Naþ ion influx increases dramatically.
A clear marker to demonstrate this is the area under the I–V
curve (AUC) (Fig. 2B). Compared to the control situation, the
AUC increases with -
427% when 10 lM BTX is present
(n ¼ 4, Table 1). BTX also changes the ion selectivity as in-
dicated by the shift in the reversal potentials (Erev) (Fig. 2B).
An average hyperpolarising shift of 5.0 mV is present when 5
lM BTX is added ðn ¼ 6Þ and a shift of 11.1 mV was noted in
the presence of 10 lM BTX ðn ¼ 4Þ (Table 1). So both the
gating and selectivity of Nav1.8 are affected by BTX, with the
effect on inactivation being the most drastic. Lower concen-
trations were also tested and we observed that 1 lM of BTX,
measured after a 900 pulse train experiment at a frequency of 1
Hz, already starts to affect Nav1.8/b1. At this concentration, a
small initial block of the current is seen, which is soon followed
by an influx of Naþ ions caused by the inhibition of the in-
activation. In addition, the activation is clearly shifted to more
hyperpolarised voltages. In order to simulate neurons in living
organisms, which have a higher firing rate than 1 Hz (e.g., 20–
50 Hz), we also tested higher frequency pulse trains. At 10 Hz,
we noticed that lower concentrations (500 nM) cause effects
that are related to higher concentrations at 1 Hz (data not
shown). Hence, we believe that in vivo the effects of BTX may
be as catastrophic at even lower concentrations
b1 at more negative membrane potentials (Fig. 2C). Thevoltage of half-maximal activation (V1=2) shifted towards morehyperpolarised voltages with -12.0 mV when 5 lM BTX wasapplied ðn ¼ 6Þ and with -14.8 mV in the presence of 10 lMBTX ðn ¼ 4Þ (Table 1). As can be seen in part IV of Fig. 2A,Nav1.8/b1 activates at )20 mV under the influence of BTX,whereas in control conditions the channels are still closed. As aresult of the total loss of inactivation and the leftward shift ofthe activation curve, the Naþ ion influx increases dramatically.A clear marker to demonstrate this is the area under the I–Vcurve (AUC) (Fig. 2B). Compared to the control situation, theAUC increases with -427% when 10 lM BTX is present(n ¼ 4, Table 1). BTX also changes the ion selectivity as in-dicated by the shift in the reversal potentials (Erev) (Fig. 2B).An average hyperpolarising shift of 5.0 mV is present when 5lM BTX is added ðn ¼ 6Þ and a shift of 11.1 mV was noted inthe presence of 10 lM BTX ðn ¼ 4Þ (Table 1). So both thegating and selectivity of Nav1.8 are affected by BTX, with theeffect on inactivation being the most drastic. Lower concen-trations were also tested and we observed that 1 lM of BTX,measured after a 900 pulse train experiment at a frequency of 1Hz, already starts to affect Nav1.8/b1. At this concentration, asmall initial block of the current is seen, which is soon followedby an influx of Naþ ions caused by the inhibition of the in-activation. In addition, the activation is clearly shifted to morehyperpolarised voltages. In order to simulate neurons in livingorganisms, which have a higher firing rate than 1 Hz (e.g., 20–50 Hz), we also tested higher frequency pulse trains. At 10 Hz,we noticed that lower concentrations (500 nM) cause effectsthat are related to higher concentrations at 1 Hz (data notshown). Hence, we believe that in vivo the effects of BTX maybe as catastrophic at even lower concentrations
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