Miura M, Yoshioka M, Miyakawa H, Kato H, Ito K I
Department of Physiology, Yamagata University School of Medicine, Yamagata 990-23.
J Neurophysiol. 1997 Nov;78(5):2269-79. doi: 10.1152/jn.1997.78.5.2269.
Properties of calcium spikes revealed during GABAA receptor antagonism in hippocampal CA1 neurons from guinea pigs. J. Neurophysiol. 78: 2269-2279, 1997. Intracellular electrical responses and changes in intracellular calcium concentration ([Ca2+]i) in response to activation of synaptic inputs and to DC injections were recorded simultaneously from CA1 pyramidal neurons (n = 42) in guinea pig hippocampal slices. In the presence of the gamma-aminobutyric acid-A (GABAA) receptor antagonists, bicuculline (mu M) and picrotoxin (10 mu M, broad (>20 ms) all-or-none spikes were induced by activation of synaptic inputs (20 pulses, 30 Hz) and were accompanied by a simultaneous rapid and large rise in [Ca2+]i (34 of 34 cells). By contrast, direct depolarizing current (0.7 nA, 1 s) induced spikes having short duration, during which time the spike firing pattern was observed not to be significantly affected. When Na+ channels were blocked by QX-314 applied intracellularly through the recording microelectrode in the presence of GABAA receptor antagonists, broad spikes were frequently generated by activation of synaptic inputs (32 of 33 cells). These broad spikes were blocked by Cd2+ (200 mu M) or in Ca2+-free medium (6 of 6 cells) but were resistant to either tetrodotoxin (TTX; 1 micro M; 6 of 6 cells) or QX-314, whereas short-duration spikes were blocked by both TTX and QX-314. Based on these findings we conclude that broad and short-duration spikes are Ca2+ and Na+ spikes, respectively. To investigate the properties of the Ca2+ spikes, antagonists of a voltage-operated Ca2+ channel were applied to the evoked responses. Nifedipine (30 mu M), a L-type Ca2+ channel blocker, suppressed the generation of Ca2+ spikes, whereas Ni2+ (100 mu M), the T- and R-type Ca2+ channel blocker, and omega-agatoxin-IVA (omega-Aga-IVA, 60 nM), a P-type Ca2+ channel blocker, had little effect on the generation of Ca2+ spikes. Nifedipine suppressed the rise in [Ca2+]i induced by synaptic inputs up to 26% of the control in the soma and 18-32% in the dendrites (n = 5), respectively, whereas Ni2+ suppressed the rise by 12-27% (n = 5) in both soma and dendrites. omega-Aga-IVA showed little effect (less than a 10% change; n = 7). These results suggest that the GABAA inhibitory system tonically suppresses dendritic Ca2+ spikes, and the L-type Ca2+ channel plays a major role in the generation of Ca2+ spikes and in Ca2+ influx.
豚鼠海马CA1神经元中GABAA受体拮抗作用期间揭示的钙峰特性。《神经生理学杂志》78: 2269 - 2279, 1997年。同时记录了豚鼠海马脑片CA1锥体神经元（n = 42）对突触输入激活和直流注入的细胞内电反应以及细胞内钙浓度（[Ca2+]i）的变化。在γ-氨基丁酸-A（GABAA）受体拮抗剂荷包牡丹碱（μM）和印防己毒素（10 μM）存在的情况下，突触输入激活（20个脉冲，30 Hz）诱导出宽（>20 ms）的全或无峰，并伴随[Ca2+]i同时快速大幅升高（34个细胞中的34个）。相比之下，直接去极化电流（0.7 nA，1 s）诱导的峰持续时间短，在此期间观察到峰发放模式未受到显著影响。当在GABAA受体拮抗剂存在的情况下通过记录微电极细胞内施加QX - 314阻断Na+通道时，突触输入激活经常产生宽峰（33个细胞中的32个）。这些宽峰被Cd2+（200 μM）或在无钙培养基中阻断（6个细胞中的6个），但对河豚毒素（TTX；1 μM；6个细胞中的6个）或QX - 314有抗性，而短持续时间的峰被TTX和QX - 314两者阻断。基于这些发现我们得出结论，宽峰和短持续时间的峰分别是钙峰和钠峰。为了研究钙峰的特性，将电压门控钙通道拮抗剂应用于诱发反应。硝苯地平（30 μM），一种L型钙通道阻滞剂，抑制了钙峰的产生，而Ni2+（100 μM），T型和R型钙通道阻滞剂，以及ω-芋螺毒素-IVA（ω-Aga-IVA，60 nM），一种P型钙通道阻滞剂，对钙峰的产生影响很小。硝苯地平分别将突触输入诱导的[Ca2+]i在胞体中的升高抑制至对照的26%，在树突中的升高抑制至18 - 32%（n = 5），而Ni2+在胞体和树突中均将升高抑制12 - 27%（n = 5）。ω-芋螺毒素-IVA显示出很小的影响（变化小于10%；n = 7）。这些结果表明，GABAA抑制系统持续抑制树突钙峰，并且L型钙通道在钙峰的产生和钙内流中起主要作用。
