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The Journal of Neurophysiology Vol. 81 No. 3 March 1999, pp. 1123-1134
Copyright ©1999 by the American Physiological Society
1Department of Oral Physiology and
Institute of Oral Biology,
Kim, Hyung-Chan and
Man-Kyo Chung.
Voltage-dependent sodium and calcium currents in acutely isolated
adult rat trigeminal root ganglion neurons. Voltage-dependent sodium (INa) and calcium
(ICa) currents in small (<30 µM) neurons from
adult rat trigeminal root ganglia were characterized with a standard
whole cell patch-clamp technique. Two types of
INa showing different sensitivity to
tetrodotoxin (TTX) were recorded, which showed marked differences in
their activating and inactivating time courses. The activation and the
steady-state inactivation kinetics of TTX-resistant
INa were more depolarized by about +20 and +30
mV, respectively, than those of TTX-sensitive
INa. Voltage-dependent ICa was recorded under the condition that
suppressed sodium and potassium currents with 10 mM Ca2+ as
a charge carrier. Depolarizing step pulses from a holding potential of
80 mV evoked two distinct inward ICa,
low-voltage activated (LVA) and high-voltage activated (HVA)
ICa. LVA ICa was first
observed at 60 to 50 mV and reached a peak at about 30 mV.
Amiloride (0.5 mM) suppressed ~60% of the LVA
ICa, whereas ~10% of HVA
ICa was inhibited by the same concentration of
the amiloride. LVA ICa was far less affected by
the presence of external Cd2+ or the replacement of
Ca2+ by 10 Ba2+ than HVA
ICa. The 
-conotoxin GVIA (-CgTx), an
N-type ICa blocker, suppressed ~65% of the
whole cell HVA ICa at the concentration of 1 µM. The -CgTx-resistant HVA ICa was
sensitive to nifedipine (10 µM), a dihydropyridine (DHP) calcium
channel antagonist, which produced an additional blockade by ~25% of
the drug-free control (~70% of the -CgTx-resistant
ICa). The combination of 10 µM nifedipine and
1 µM -CgTx left ~13% of the drug-free control
ICa unblocked. The DHP agonist S()-BayK8644 (5 µM) shifted the activation of the HVA ICa to
more negative potentials and increased its maximal amplitude.
Additionally, S()-BayK8644 caused the appearance of a slowed
component of the tail current. These results clearly demonstrate that
the presence of two types of sodium channels, TTX sensitive and
resistant, and three types of calcium channels, T, L, and N type, in
the small-sized adult rat trigeminal ganglion neurons.
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