Possible modulatory role of voltage-activated Ca2+ currents determining the membrane properties of isolated pyramidal neurones of the rat dorsal cochlear nucleus
C. Harasztosi et al., Possible modulatory role of voltage-activated Ca2+ currents determining the membrane properties of isolated pyramidal neurones of the rat dorsal cochlear nucleus, BRAIN RES, 839(1), 1999, pp. 109-119
Voltage-activated Ca2+ currents have been studied in pyramidal cells isolat
ed enzymatically from the dorsal cochlear nuclei of 6-11-day-old Wistar rat
s, using whole-cell voltage-clamp. From hyperpolarized membrane potentials,
the neurones exhibited a T-type Ca2+ current on depolarizations positive t
o - 90 mV (the maximum occurred at about -40 mV). The magnitude of the T-cu
rrent varied considerably from cell to cell (-56 to -852 pA) while its stea
dy-state inactivation was consistent (E-50= -88.2 +/- 1.7 mV, s = - 6.0 +/-
0.4 mV). The maximum of high-voltage activated (HVA) Ca2+ currents was obs
erved at about -15 mV. At a membrane potential of -10 mV the L-type Ca2+ ch
annel blocker nifedipine (10 mu M) inhibited approximately 60% of the HVA c
urrent, the N-type channel inhibitor omega-Conotoxin GVIA (2 mu M) reduced
the current by 25% while the P/Q-type channel blocker omega-Agatoxin IVA (2
00 nM) blocked a further 10%. The presence of the N- and P/Q-type Ca2+ chan
nels was confirmed by immunochemical methods. The metabotropic glutamate re
ceptor agonist(+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (200 mu
M) depressed the HVA current in every cell studied (a block of approximate
ly 7% on an average). The GABA(B) receptor agonist baclofen (100 mu M) reve
rsibly inhibited 25% of the HVA current. Simultaneous application of omega-
Conotoxin GVIA and baclofen suggested that this inhibition could be attribu
ted to the nearly complete blockade of the: N-type channels. Possible physi
ological functions of the voltage-activated Ca2+ currents reported in this
work are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.