Cf. Hsiao et Sk. Chandler, CHARACTERISTICS OF A FAST TRANSIENT OUTWARD CURRENT IN GUINEA-PIG TRIGEMINAL MOTONEURONS, Brain research, 695(2), 1995, pp. 217-226
A fast transient voltage dependent outward current (TOC) in trigeminal
motoneurons (TMNs) was studied in guinea pig brainstem slices by use
of sharp electrodes in combination with single electrode voltage clamp
techniques. In solutions containing TTX, low Ca2+/Mn2+ and 20 mM TEA
this current activated around -55 to -60 mV from holding potentials ne
gative to resting potential, obtained its peak amplitude within 5 ms a
nd decayed as a single exponential with a time constant of 6-8 ms. Hal
f maximal values for inactivation and activation were -72 and -37 mV,
respectively. Bath application of 5 mM 4-AP suppressed this current by
approximately 90% and eliminated the early depolarizing transient mem
brane rectification observed in response to a constant depolarizing cu
rrent pulse, prolonged the action potential duration, and reduced the
threshold voltage and delay to onset of the action potential. It is su
ggested that this current resembles the typical A-current observed in
many CNS neurons and, as a result of its voltage and time dependent pr
operties, could contribute to control of motoneuronal discharge and ti
ming of burst onset during rhythmical jaw movements. Therefore, any ce
llular models of masticatory activity should include the properties of
this current.