The passive and active electrical properties of freshly dispersed single cells of the guinea-pig ureter were investigated using standard patch-clamp techniques. 2. Action potentials, having a rapid rising phase and a prolonged plateau, were recorded on passing depolarizing currents through the patch pipette when 'near-normal' physiological gradients were established across the cell membrane (5.9 mM-K+, 1.5 mM-Ca2+ in the bath; 126 mM-K+ in the pipette). 3. Under voltage clamp, depolarization to potentials positive of -50 mV (from a holding potential of -70 or -80 mV) triggered a net inward current which reached a peak in 5-10 ms and then slowly inactivated. 4. The averaged membrane current to depolarization to potentials between -30 and 0 mV showed two distinct patterns after the peak of the inward current; the membrane current either moved slowly outward over 400 ms or there was one or more transient outward currents superimposed on the slowly decreasing inward current. Both outward currents were blocked when 5 mM-tetraethylammonium (TEA) was added to the bathing solution, resulting in an increased inward current at all potentials. 5. Replacing the extracellular Ca2+ with Co2+ (1.5-5 mM) blocked the inward current and the outward currents to reveal another transient outward current (voltage activated) which activated rapidly to reach a peak within 5 ms and which inactivated exponentially with a time constant of 10 ms. This voltage-activated outward current was inactivated if the membrane was held at -50 mV, but could be reactivated by short hyperpolarizing pre-pulses. The amplitude of this transient current in response to a fixed depolarization (to 0 mV) was half-maximum when the hyperpolarizing pre-pulse was to -66 mV. The voltage-activated outward current was reduced in amplitude when the extracellular potassium was raised to 46 mM or upon exposure to 1 mM-4-aminopyridine (4-AP), but was not affected by 5 mM-TEA. 6. Replacing K+ in the pipette and bathing solution with caesium (Cs) blocked all outward currents, revealing the time course and voltage dependence of the inward current, which could be carried by Ca2+ or Ba2+ with little effect on its rate of inactivation. 7. It was concluded that the inward current recorded in single ureter cells was due to the flow of current through voltage-activated Ca2+ channels. The TEA-sensitive outward currents, whether transient or slowly activating, are presumably K+ channels activated by Ca2+.(ABSTRACT TRUNCATED AT 400 WORDS)
摘要
运用标准的膜片钳技术研究了豚鼠输尿管新鲜分离的单个细胞的被动和主动电特性。2. 当在细胞膜上建立“接近正常”的生理梯度时（浴液中含5.9 mM - K⁺、1.5 mM - Ca²⁺；微电极内液含126 mM - K⁺），通过膜片微电极通入去极化电流时，记录到具有快速上升相和延长平台期的动作电位。3. 在电压钳制下，从 - 70或 - 80 mV的钳制电位去极化到 - 50 mV以上的电位时，会触发一个内向净电流，该电流在5 - 10 ms内达到峰值，然后缓慢失活。4. 内向电流峰值后，平均膜电流对 - 30至0 mV电位的去极化表现出两种不同模式；膜电流要么在400 ms内缓慢外向移动，要么在缓慢下降的内向电流上叠加一个或多个瞬时外向电流。当向浴液中加入5 mM - 四乙铵（TEA）时，两种外向电流均被阻断，导致所有电位下内向电流增加。5. 用Co²⁺（1.5 - 5 mM）替代细胞外Ca²⁺可阻断内向电流和外向电流，从而揭示另一种瞬时外向电流（电压激活），该电流在5 ms内迅速激活达到峰值，并以10 ms的时间常数指数失活。如果将膜电位钳制在 - 50 mV，这种电压激活的外向电流会失活，但可通过短暂的超极化预脉冲重新激活。当超极化预脉冲为 - 66 mV时，该瞬时电流对固定去极化（至0 mV）的响应幅度为最大值的一半。当细胞外钾离子浓度升至46 mM或暴露于1 mM - 4 - 氨基吡啶（4 - AP）时，电压激活的外向电流幅度减小，但不受5 mM - TEA影响。6. 用铯（Cs）替代微电极内液和浴液中的K⁺可阻断所有外向电流，揭示内向电流的时间进程和电压依赖性，内向电流可由Ca²⁺或Ba²⁺携带，对其失活速率影响较小。7. 得出结论，单个输尿管细胞中记录到的内向电流是由于电流通过电压激活的Ca²⁺通道流动所致。TEA敏感的外向电流，无论是瞬时的还是缓慢激活的，推测是由Ca²⁺激活的K⁺通道。（摘要截短至400字）
