Voltage-dependent facilitation of calcium channels in rat neostriatal neurons.
1. Voltage-dependent facilitation of Ca2+ channels was studied in acutely isolated adult rat neostriatal neurons. Particular attention was paid to the facilitation of L-type channels. 2. In the absence of neuromodulators, the current-voltage relationship for whole cell Ba2+ currents was enhanced by a prepulse to +100 mV. The median enhancement at -20 mV was nearly 60%. The voltage dependence and kinetics of the processes underlying the facilitation were similar to those reported in other neurons. N-, P-, Q-, and L-type currents contributed to the observed facilitation. 3. Voltage-dependent facilitation of L-type currents was studied by subtracting nifedipine-insensitive currents from control currents. Although the kinetics were similar to those of the whole cell currents, the half-activation voltage for facilitation of L-type currents [half-activation voltage (Vh) = -0.6 mV, slope factors (Vc) = 11.8 mV, [n = 5] was significantly less depolarized than that of the pooled currents (Vh = 47.3 mV, Vc = 12.3 mV, n = 7). 4. Repetitive depolarization with spikelike waveforms was also able to induce facilitation of L-type currents, suggesting that facilitation was not simply a consequence of a modal shift in gating like that induced by Bay K 8644. 6. Combined whole cell recording and single-cell reverse transcription-polymerase chain reaction amplification revealed that neostriatal medium spiny neurons expressed detectable levels of either class C or class D L-type channel alpha 1, subunit mRNA. Both neurons expressing class C L-type channels and neurons expressing class D L-type channels exhibited voltage-dependent facilitation.
Song
W J
WJ
Department of Anatomy and Neurobiology, College of Medicine, University of Tennessee, Memphis, USA.
Surmeier
D J
DJ
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000502:physiology*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D015640:Ion Channel Gating; D007473:Ion Channels / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000502:physiology; D017072:Neostriatum / Q000166:cytology / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D017711:Nonlinear Dynamics; D018408:Patch-Clamp Techniques; D016133:Polymerase Chain Reaction / Q000379:methods; D051381:Rats; D014158:Transcription, Genetic
D002120:Calcium Channel Agonists; D015220:Calcium Channels; D007473:Ion Channels; D001464:Barium; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester