Shuba M F, Smirnov S V
J Physiol. 1986 Nov;380:1-16. doi: 10.1113/jphysiol.1986.sp016268.
A single glass micropipette voltage-clamp technique was used to study a potential-dependent calcium inward current in isolated smooth muscle cells of the guinea-pig taenia caeci. Experiments were performed at 22-24 degrees C. With potassium as the main cation in the pipette solution, a transient inward current appeared in response to a depolarizing pulse, followed by an outward current. The replacement of potassium ions by caesium ions and TEA (tetraethyl-ammonium) in the pipette solution resulted in an effective suppression of potassium outward current permitting a study of the calcium current solely. The calcium inward current was blocked by 5 mM-cobalt and 5 X 10(-6) M-verapamil. Activation of the calcium current occurred at a membrane potential of between -35 and -25 mV. The calcium current was maximal in the potential range +10 to +20 mV and did not reverse even at +60 mV. Inactivation of the calcium current had a complex nature. It did not inactivate completely even during depolarizations lasting many seconds. During the first 400 ms the decay of the calcium current followed a time course described by two exponentials. The fast time constant of decay was in the range of 40 to 53 ms (n = 3) and the slow time constant was approximately 10-fold greater (at 0 mV). The fast time constant did not depend on the membrane potential while the slow time constant decreased with depolarization. Availability of the calcium current was estimated in double-pulse experiments. It had a U-shaped dependence on the conditioning potential; maximal inactivation was observed at potentials corresponding to the maximal calcium current. It was suggested that a component of inactivation was dependent on the calcium current which flowed. Calculations of calcium entry at various depolarizations showed that large amounts of calcium ions enter the cell. Also, it was suggested that calcium ions are effectively bound within the smooth muscle cell.
采用单玻璃微电极电压钳技术，研究豚鼠盲肠带孤立平滑肌细胞中电压依赖性钙内向电流。实验在22 - 24℃下进行。以钾作为微电极溶液中的主要阳离子时，去极化脉冲会引发一个短暂的内向电流，随后是外向电流。用铯离子和TEA（四乙铵）替代微电极溶液中的钾离子，可有效抑制钾外向电流，从而仅对钙电流进行研究。5 mM - 钴和5×10⁻⁶ M - 维拉帕米可阻断钙内向电流。钙电流在膜电位为 - 35至 - 25 mV之间激活。钙电流在 + 10至 + 20 mV的电位范围内最大，甚至在 + 60 mV时也不反转。钙电流的失活具有复杂的性质。即使在持续数秒的去极化过程中，它也不会完全失活。在最初的400 ms内，钙电流的衰减遵循由两个指数描述的时间进程。快速衰减时间常数在40至53 ms范围内（n = 3），缓慢时间常数大约大10倍（在0 mV时）。快速时间常数不依赖于膜电位，而缓慢时间常数随去极化而减小。在双脉冲实验中估计了钙电流的可用性。它对条件电位具有U形依赖性；在对应于最大钙电流的电位下观察到最大失活。有人认为失活的一个成分依赖于所流动的钙电流。对不同去极化程度下钙内流的计算表明，大量钙离子进入细胞。此外，有人认为钙离子在平滑肌细胞内被有效结合。
