Higashi H, Sugita S, Matsunari S, Nishi S
Department of Physiology, Kurume University School of Medicine, Japan.
Neuroscience. 1990;34(1):35-47. doi: 10.1016/0306-4522(90)90302-k.
Effects of organic Ca channel blockers, Ca channel activators and omega-conotoxin on guinea-pig hippocampal CA1 neurons in vitro preparations were studied with intracellular recording methods. Most of the Ca channel blockers, such as prenylamine, D 600, flunarizine, nifedipine, cinnarizine and nicardipine (0.2-4 microM), raised the threshold for Na-dependent spike generation and decreased the amplitude of the spike afterhyperpolarization. Verapamil (5 microM) and diltiazem (5 microM) did not significantly alter the threshold and amplitude of the Na spike. Action potentials elicited in the presence of either tetrodotoxin (0.5 microM) and tetraethylammonium (20 mM) or tetrodotoxin (0.5 microM) and Ba (1.25 mM) consisted of an initial spike component followed by a long depolarization. Both responses were abolished by addition of Co (2 mM) or Cd (0.25-0.5 mM), or by superfusion with a low Ca (0.25 mM)-high Mg(15 mM) medium, indicating that the potentials resulted from Ca entry. The Ca-dependent slow depolarization was preferentially blocked by most of the organic Ca channel blockers at approximately one-third the concentrations (0.1-2 microM) which were required to shorten the Ca spike. When the cell in a solution containing tetrodotoxin (0.5 microM), Co (2 mM) and 4-aminopyridine (2 mM) was hyperpolarized and then depolarized by passing current pulses across the membrane, a transient depolarizing hump occurred on the decay phase of the electrotonic potential. This transient depolarization was abolished by Co (2 mM), Ni (2 mM) or most of the organic Ca channel blockers (0.2-5 microM). Diltiazem (5 microM) did not significantly change these Ca-dependent potentials. The evoked excitatory postsynaptic potential was very resistant to the Ca channel blockers. Approximately 2-10 times higher concentrations (0.5-3 microM) were necessary to decrease the excitatory postsynaptic potential amplitude than to shorten the Ca spike. On the other hand, the minimal concentrations and order of potencies of the Ca channel blockers for depressing the evoked inhibitory postsynaptic potential and for elevating the threshold for Na spike generation were almost the same. Dihydropyridine Ca channel activators, such as Bay K 8644, CGP 28 392 and YC 170 at low concentrations (0.1-1 microM), decreased the Ca spike, the Ca-dependent slow depolarization and the evoked synaptic potentials, while the substances augmented the Ca-dependent transient depolarization. On the other hand, omega-conotoxin (5 microM) reversibly depressed the Ca spike and slow depolarization to the same degree, without affecting the transient depolarization and the evoked excitatory or inhibitory postsynaptic potentials.(ABSTRACT TRUNCATED AT 400 WORDS)
采用细胞内记录方法，研究了有机钙通道阻滞剂、钙通道激活剂和ω-芋螺毒素对豚鼠海马CA1神经元体外标本的作用。大多数钙通道阻滞剂，如普尼拉明、D 600、氟桂利嗪、硝苯地平、桂利嗪和尼卡地平（0.2 - 4微摩尔），提高了钠依赖性动作电位产生的阈值，并降低了动作电位超极化后的幅度。维拉帕米（5微摩尔）和地尔硫䓬（5微摩尔）对钠动作电位的阈值和幅度无明显影响。在存在河豚毒素（0.5微摩尔）和四乙铵（20毫摩尔）或河豚毒素（0.5微摩尔）和钡（1.25毫摩尔）时诱发的动作电位由一个初始动作电位成分和随后的长去极化组成。加入钴（2毫摩尔）或镉（0.25 - 0.5毫摩尔），或用低钙（0.25毫摩尔） - 高镁（15毫摩尔）培养基灌流，两种反应均被消除，表明这些电位是由钙内流引起的。大多数有机钙通道阻滞剂在约为缩短钙动作电位所需浓度（0.1 - 2微摩尔）的三分之一时，优先阻断钙依赖性慢去极化。当细胞处于含有河豚毒素（0.5微摩尔）、钴（2毫摩尔）和4 - 氨基吡啶（2毫摩尔）的溶液中，经膜通过电流脉冲使其超极化然后去极化时，在电紧张电位的衰减相出现一个短暂的去极化波峰。这种短暂去极化被钴（2毫摩尔）、镍（2毫摩尔）或大多数有机钙通道阻滞剂（0.2 - 5微摩尔）消除。地尔硫䓬（5微摩尔）对这些钙依赖性电位无明显影响。诱发的兴奋性突触后电位对钙通道阻滞剂非常耐受。降低兴奋性突触后电位幅度所需的浓度大约比缩短钙动作电位所需浓度高2 - 10倍。另一方面，钙通道阻滞剂抑制诱发的抑制性突触后电位和提高钠动作电位产生阈值的最小浓度和效能顺序几乎相同。二氢吡啶类钙通道激活剂，如低浓度（0.1 - 1微摩尔）的Bay K 8644、CGP 28 392和YC 170，降低了钙动作电位、钙依赖性慢去极化和诱发的突触电位，而这些物质增强了钙依赖性短暂去极化。另一方面，ω-芋螺毒素（5微摩尔）可逆地同等程度抑制钙动作电位和慢去极化，而不影响短暂去极化以及诱发的兴奋性或抑制性突触后电位。（摘要截短于400字）
