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Inhibitory effects of Metergoline on Nav1.2 voltage-
dependent sodium channel
Sanung Eom , Jaeeun Lee , Chaelin Kim , Shinhui Lee and Jun-Ho Lee *
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1 Department of Biotechnology, Chonnam National University, Gwangju, Korea
ABSTRACT RESULTS
Metergoline is an ergot-derived psychoactive drug that acts as a Figure 1. Effects of metergoline on neuronal Nav1.2 channel Figure 4. Use-dependent blockade of the Nav1.2 channel current
ligand for serotonin and dopamine receptors. In the present study, currents and the current-voltage relationship by metergoline.
we investigated the effects of metergoline on neuronal Nav1.2
voltage-dependent sodium channel activity. The two-microelectrode
voltage clamp technique was used to study the regulation of
metergoline on Na+ current in Xenopus oocytes expressing cRNA-
encoding Nav1.2 α and β1 subunits in the rat brain. In oocytes that
expressed neuronal Na+ channels, metergoline induced inhibitory
effects on the peak of Na+ currents. The metergoline-induced tonic
inhibitions of peak Na+ currents were voltage- and concentration-
dependent and reversible. The half maximal inhibitory concentration
(IC50) in peak currents of rat brain Na1.2 channels was 4.6 ± 1.3
M. Metergoline treatment produced a 3.6 ± 0.4 mV depolarizing
shift in the activation voltage but did not alter the steady-state
inactivation voltage. In addition, metergoline produced a use-
dependent blockade of the Na+ channel after high-frequency
stimulation, indicating that metergoline could exert an inhibitory
effect on the open state of the Na+ channel. Taken together, these
results indicate that metergoline might regulate neuronal Nav1.2
voltage-dependent channels that are expressed in Xenopus oocytes.
Our study further suggests that metergoline can be an important Figure 2. Tonic inhibition of Nav1.2 channel currents by
pharmacological target as a potent inhibitor of neuronal Nav1.2 metergoline and lidocaine.
channels
MATERIALS AND METHODS
Materials
Rat brain Na+ channel Nav1.2 α and β.1 subunits (University of
California, Irvine, CA, USA). ). Metergoline (Tocris bioscience, MS,
USA) The cDNA encoding the Nav1.2 α and β.1 subunits
(University of California, Irvine, CA, USA)
Cell preparation
Xenopus laevis (Xenopus I, Ann Arbor, MI, USA)
SUMMARY AND CONCLUSION
In vitro transcription and expression
In vitro transcription kit (mMessage mMachine; Ambion) In this study, we characterized the effects of metergoline on
cDNA were transcribed cRNA as protocols brain Na+ channels expressed in Xenopus oocytes, and
cRNA (10-40ng/40nl), Automatic Oocyte injector (Drummond found four major results. First, metergoline induced tonic
Scientific), Incubation (18℃, 2-3 day) inhibition of peak Na+ currents via interactions with the
Figure 3. The effect of metergoline on steady-state activation resting state of the Na+ channel, and inhibition of Na+
Data recording and inactivation of Nav1.2 channel current. currents by metergoline was dose-dependent and reversible
Oocyte Clamp (OC-725C; Warner Instruments, Hamden, CT, USA), (Fig. 2). Second, metergoline showed reversible current-
and stimulation and data acquisition were controlled using a pClamp and voltage-dependent reductions in peak Na+ currents.
10.2 (Axon Instruments, Union City, CA, USA). Third, metergoline affected the steady-state activation, but
not inactivation, voltages of the Na+ channel. Fourth,
Data analysis metergoline produced a use-dependent blockade of the Na+
Two-microelectrode voltage-clamp recording (Oocyte Clamp (OC- channel following high-frequency stimulation.
725C), Digidata 1200A) were conducted within 5-6 days. The pharmacological actions of metergoline on Na+
Origin software (Origin, Northampton, MA, USA) channels are indeed very similar to those of antidepressants,
y/ymax = [A]nH/([A]nH + [IC50]n) which elicit strong usage-dependent blockage of Nav1.2
The conductance (gNa) channel currents and have the highest affinities toward the
gNa = INa/(Vg – Vr), open state of Na+ channels. In this respect, metergoline acts
where INa is the peak amplitude of the Na+ current, more like an open Na+ channel blocker such as ranolazine
Vg is the test potential, or duloxetine.
Vr is the reversal potential for Na+. In conclusion, we used neural Na+ channels expressed in a
The conductance-voltage curves were drawn according to the Xenopus oocyte model system to investigate whether
equation: metergoline blocks the resting and open states of neuronal
gNa/maxgNa = 1/{1+ exp [(Vg0.5 – Vg)/kg]}, Na1.2 channels. A detailed study of the interactions
where maxgNa is the maximum value for gNa, between metergoline and the Nav1.2 channel suggests that
Vg0.5 is the potential at which gNa is 0.5 maxgNa, metergoline is a potent open-channel blocker for Nav1.2 in
kg is the slope factor (potential required for an e-fold change). a concentration-, voltage-, and use-dependent manner.
The steady-state inactivation curves were drawn according to the These results provide important insights into brain Na+
equation: channel regulation induced by metergoline and suggest a
INa/maxINa = 1/{1 + exp [(Vh – Vh0.5)/kh]}, possible molecular basis for the analgesic and
where Vh is pre-pulse potential, neuroprotective effects of metergoline.
Vh0.5 is the potential at which INa is 0.5 maxINa,
kh is the slope factor. a
