Coulombe A, Lefèvre I A, Baro I, Coraboeuf E
Laboratoire de Physiologie Comparée, Laboratoire des Biomembranes, des Ensembles Neuronaux (CNRS URA 1121), Université Paris-XI, Orsay.
J Membr Biol. 1989 Oct;111(1):57-67. doi: 10.1007/BF01869209.
Ca2+- and Ba2+-permeable channel activity from adult rat ventricular myocytes, spontaneously appeared in the three single-channel recording configurations: cell-attached, and excised inside-out or outside-out membrane patches. Single-channel activity was recorded at steady-state applied membrane potentials including the entire range of physiologic values, and displayed no "rundown" in excised patches. This activity occurred in irregular bursts separated by quiescent periods of 5 to 20 min in cell-attached membrane patches, whereas in excised patch experiments, this period was reduced to 2 to 10 min. During activity, a variety of kinetic behaviors could be observed with more or less complex gating patterns. Three conductance levels: 22, 45 and 78 pS were routinely observed in the same excised membrane patch, sometimes combining to give a larger level. These channels were significantly permeable to divalent cations and showed little or no permeability to potassium or sodium ions. The inorganic blockers of voltage-gated Ca channels, cobalt (2 mM), cadmium (0.5 mM) or nickel (3 mM), had no apparent effect on these spontaneous unitary currents carried by barium ions. Under 10(5) M Bay K 8644 or nitrendipine, the activity was clearly increased in about half of the tested excised inside-out membrane patches. Both dihydropyridines enhanced openings of the larger conductance level, which was only very occasionally seen under control conditions. When the single-channel activity became sustained under 5 x 10(-6) M Bay K 8644, it was possible to calculate the mean unitary current at different membrane potentials and show that the mean current value increased with membrane potential.
成年大鼠心室肌细胞的钙离子和钡离子通透通道活性，自发地出现在三种单通道记录模式中：细胞贴附式、内面向外或外面向外的膜片钳模式。在包括整个生理值范围的稳态施加膜电位下记录单通道活性，并且在切除的膜片中未显示“衰减”。这种活性在细胞贴附膜片中以不规则的爆发形式出现，爆发之间有5至20分钟的静止期，而在切除膜片实验中，这个时期缩短至2至10分钟。在活性期间，可以观察到各种动力学行为，门控模式或多或少复杂。在同一切除的膜片中通常观察到三种电导水平：22、45和78 pS，有时合并给出更大的水平。这些通道对二价阳离子具有显著通透性，对钾离子或钠离子几乎没有或没有通透性。电压门控钙通道的无机阻滞剂钴（2 mM）、镉（0.5 mM）或镍（3 mM），对这些由钡离子携带的自发单通道电流没有明显影响。在10^5 M Bay K 8644或尼群地平作用下，约一半测试的内面向外切除膜片中活性明显增加。两种二氢吡啶都增强了较大电导水平的开放，这在对照条件下很少见。当单通道活性在5×10^-6 M Bay K 8644作用下持续时，可以计算不同膜电位下的平均单通道电流，并表明平均电流值随膜电位增加。
