Sheets M F, Scanley B E, Hanck D A, Makielski J C, Fozzard H A
Biophys J. 1987 Jul;52(1):13-22. doi: 10.1016/S0006-3495(87)83183-1.
Open channel properties of canine cardiac Purkinje cell Na+ channels were studied with single channel cell-attached recording and with whole cell macroscopic current recording in internally perfused cells. Single channel currents and membrane currents increased with an increase in Na+ concentration, but showed evidence of saturation. Assuming first-order binding, the Km for Na+ was 370 mM. PCs/PNa was 0.020 and PK/PNa was 0.094. The current-voltage relationship for single channels showed prominent flattening in the hyperpolarizing direction. This flattening was accentuated by 10 mM Ca2+ and was greatly reduced in O mM Ca2+, indicating that the rectification was a consequence of Ca2+ block of the Na+ channels. A similar instantaneous current-voltage relationship was seen for the whole cell membrane currents. These results demonstrate that the cardiac channel shows substantial Ca2+ block, although it is relatively insensitive to tetrodotoxin. The Na+ and Ca2+ binding properties could be modeled by the four-barrier Eyring rate theory model, with similar values to those reported for the neuroblastoma Na+ channel (Yamamoto, D.,J.Z. Yeh, and T. Narahashi, 1984, Biophys J., 45:337-344).
利用单通道细胞贴附记录法以及对内部灌流细胞进行全细胞膜片宏观电流记录，研究了犬心脏浦肯野细胞钠离子通道的开放通道特性。单通道电流和膜电流随钠离子浓度升高而增加，但表现出饱和迹象。假设为一级结合，钠离子的米氏常数（Km）为370 mM。 PCs/PNa为0.020，PK/PNa为0.094。单通道的电流-电压关系在超极化方向上呈现出明显的平缓。这种平缓在10 mM Ca2+存在时加剧，而在0 mM Ca2+时大大减弱，表明这种整流是钠离子通道被Ca2+阻断的结果。全细胞膜电流也呈现出类似的瞬时电流-电压关系。这些结果表明，心脏通道表现出显著的Ca2+阻断，尽管它对河豚毒素相对不敏感。钠离子和钙离子的结合特性可以用四屏障艾林速率理论模型来模拟，其值与报道的神经母细胞瘤钠离子通道的值相似（山本，D.，J.Z.叶，和T. Narahashi，1984，《生物物理杂志》，45:337 - 344）。
