Calcium inward currents were recorded from relaxed enzymatically isolated smooth muscle cells from the rabbit epicardial left descending coronary artery using a single-pipette voltage-clamp technique. Outward K+ currents were blocked with CsCl-tetraethylammonium-filled pipette solutions. 2. Relaxed coronary smooth muscle cells had a maximum diameter of 8.6 +/- 0.6 microns and a cell length of 96.7 +/- 3.3 microns when bathed in 2.5 mM [Ca2+]o. The average resting membrane potential at room temperature was -32 +/- 10 mV. The mean cell capacitance was 18.5 +/- 1.7 pF and the input resistance was 3.79 +/- 0.58 G omega. 3. Depolarizing voltage-clamp steps from a holding potential of -80 mV elicited a single time- and voltage-dependent inward current which was dependent upon extracellular [Ca2+]. In 2.5 mM [Ca2+]o, the inward current was activated at a potential of -40 mV and peaked at +10 mV. This current was inhibited by 0.5 mM-CdCl2 and 1 microM-nifedipine and was enhanced with 1 microM-Bay K 8644. No detectable low-threshold, rapidly inactivating T-type calcium current was observed. 4. The apparent reversal potential of this inward current in 2.5 mM [Ca2+]o was +70 mV and shifted by 33.0 mV per tenfold increase in [Ca2+]o. This channel was also more permeable to barium and strontium ions than to calcium ions. 5. Single calcium channel recordings with 110 mM-Ba2+ as the charge carrier revealed a mean slope conductance of 20.7 +/- 0.8 pS. 6. This calcium current (ICa) exhibited a strong voltage-dependent inactivation process. However, the steady-state inactivation curve (f infinity) displayed a slight nonmonotonic, U-shaped dependence upon membrane potential. The potential at which half of the channels were inactivated was -27.9 mV with a slope factor of 6.9 mV. The steady-state activation curve (d infinity) was also well-described by a Boltzmann distribution with a half-activation potential at -4.4 mV and a slope factor of -63 mV. ICa was fully activated at approximately +20 mV. 7. The rate of inactivation was dependent upon the species of ion carrying the current. Both Sr2+ and Ba2+ decreased the rate as well as the degree of inactivation. The tau f (fitted time constant of inactivation) curve displayed a U-shaped relationship in 2.5 mM [Ca2+]o. The reactivation process was voltage dependent and could be described by a single exponential. 8. The current amplitude and the inactivation kinetics were temperature dependent.(ABSTRACT TRUNCATED AT 400 WORDS)
摘要
使用单电极电压钳技术，从兔心外膜左冠状动脉酶解分离的松弛平滑肌细胞中记录钙内向电流。向外的钾电流用充满氯化铯 - 四乙铵的电极溶液阻断。2. 当浸浴在2.5 mM [Ca2+]o中时，松弛的冠状动脉平滑肌细胞最大直径为8.6±0.6微米，细胞长度为96.7±3.3微米。室温下平均静息膜电位为 -32±10 mV。平均细胞电容为18.5±1.7 pF，输入电阻为3.79±0.58 GΩ。3. 从 -80 mV的钳制电位进行去极化电压钳步阶，引发单一的时间和电压依赖性内向电流，该电流依赖于细胞外[Ca2+]。在2.5 mM [Ca2+]o中，内向电流在 -40 mV电位时被激活，在 +10 mV时达到峰值。该电流被0.5 mM - CdCl2和1 μM硝苯地平抑制，并被1 μM Bay K 8644增强。未观察到可检测的低阈值、快速失活的T型钙电流。4. 在2.5 mM [Ca2+]o中，该内向电流的表观反转电位为 +70 mV，[Ca2+]o每增加10倍，反转电位偏移33.0 mV。该通道对钡离子和锶离子的通透性也高于钙离子。5. 以110 mM Ba2+作为载流子的单钙通道记录显示平均斜率电导为20.7±0.8 pS。6. 该钙电流（ICa）表现出强烈的电压依赖性失活过程。然而，稳态失活曲线（f无穷大）对膜电位呈现轻微的非单调U形依赖性。通道半数失活时的电位为 -27.9 mV，斜率因子为6.9 mV。稳态激活曲线（d无穷大）也可用玻尔兹曼分布很好地描述，半激活电位为 -4.4 mV，斜率因子为 -63 mV。ICa在约 +20 mV时完全激活。7. 失活速率取决于携带电流的离子种类。Sr2+和Ba2+都降低了失活速率以及失活程度。在2.5 mM [Ca2+]o中，tau f（拟合的失活时间常数）曲线呈现U形关系。再激活过程是电压依赖性的，可用单一指数描述。8. 电流幅度和失活动力学是温度依赖性的。（摘要截断于400字）
