Wu R L, Barish M E
Division of Neurosciences, Beckman Research Institute of the City of Hope, Duarte, California 91010.
J Neurosci. 1992 Jun;12(6):2235-46. doi: 10.1523/JNEUROSCI.12-06-02235.1992.
Transient potassium currents in mammalian central neurons influence both the repolarization of single action potentials and the timing of repetitive action potential generation. How these currents are integrated into neuronal function will depend on their specific properties: channel availability at the resting potential, activation threshold, inactivation rate, and current density. We here report on the voltage-gated transient potassium currents in embryonic mouse hippocampal neurons dissected at embryonic days 15-16 and grown in dissociated cell culture for up to 3 d. Two transient potassium currents, A-current and D-current, were isolated based on steady state inactivation and sensitivity to 4-aminopyridine (4-AP) and dendrotoxin (DTx). A-current had an activation threshold of approximately -50 mV and was half-inactivated at approximately -81 mV. A-current relaxations at voltages between -40 and +40 mV could be fit by single exponential functions with time constants of 20-25 msec; these time constants showed little sensitivity to voltage. In contrast, D-current had an activation threshold of between -40 and -30 mV and was half-inactivated at approximately -22 mV. D-current inactivation was voltage dependent; time constants of fitted exponential functions ranged from approximately 7 sec at -40 mV to 200 msec at +40 mV. A slower component of inactivation was also evident. D-current was preferentially blocked by 4-AP (100 microM) and DTx (1 microM). Operationally, A- and D-currents could be cleanly separated based on conditioning pulse potential and 4-AP sensitivity. Total transient potassium current amplitude increased during the time that neurons were in culture (recordings were made between 2 hr after dissociation and 3 d in culture). When normalized for cell capacitance (an index of membrane area), A-current density (pA/pF) decreased and D-current density increased, even during a period between days 1 and 3 when total transient current density remained constant. This observation suggests that A- and D-currents may be reciprocally modulated. Since blockade of D-current (with 100 microM 4-AP) increased both action potential duration and repetitive firing in response to constant current stimulation, long-term modulation of the A-current:D-current ratio may affect the excitability of hippocampal neurons.
哺乳动物中枢神经元中的瞬时钾电流既影响单个动作电位的复极化，也影响重复动作电位产生的时间。这些电流如何整合到神经元功能中，将取决于它们的特定属性：静息电位时的通道可用性、激活阈值、失活速率和电流密度。我们在此报告在胚胎第15 - 16天解剖并在解离细胞培养中生长长达3天的胚胎小鼠海马神经元中的电压门控瞬时钾电流。基于稳态失活以及对4 - 氨基吡啶（4 - AP）和树突毒素（DTx）的敏感性，分离出两种瞬时钾电流，即A电流和D电流。A电流的激活阈值约为 - 50 mV，在约 - 81 mV时半失活。在 - 40至 + 40 mV之间电压下的A电流松弛可用时间常数为20 - 25毫秒的单指数函数拟合；这些时间常数对电压的敏感性很小。相比之下，D电流的激活阈值在 - 40至 - 30 mV之间，在约 - 22 mV时半失活。D电流失活依赖于电压；拟合指数函数的时间常数范围从 - 40 mV时的约7秒到 + 40 mV时的200毫秒。失活的较慢成分也很明显。D电流优先被100微摩尔的4 - AP和1微摩尔的DTx阻断。在操作上，基于预处理脉冲电位和4 - AP敏感性，可以清晰地分离A电流和D电流。在神经元培养期间（在解离后2小时至培养3天之间进行记录），总瞬时钾电流幅度增加。当以细胞电容（膜面积的指标）进行归一化时，即使在第1天至第3天期间总瞬时电流密度保持恒定时，A电流密度（皮安/皮法）下降而D电流密度增加。这一观察结果表明A电流和D电流可能相互调节。由于用100微摩尔的4 - AP阻断D电流会增加动作电位持续时间以及对恒定电流刺激的重复放电，A电流与D电流比值的长期调节可能会影响海马神经元的兴奋性。
