Amberg Gregory C, Baker Salah A, Koh Sang Don, Hatton William J, Murray Keith J, Horowitz Burton, Sanders Kenton M
Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV 89557, USA.
J Physiol. 2002 Oct 15;544(2):417-28. doi: 10.1113/jphysiol.2002.025171.
A-type currents are rapidly inactivating potassium currents that operate at subthreshold potentials. A-type currents have not been reported to occur in the phasic muscles of the stomach. We used conventional voltage-clamp techniques to identify and characterize A-type currents in myocytes isolated from the murine antrum. A-type currents were robust in these cells, with peak current densities averaging 30 pA pF(-1) at 0 mV. These currents underwent rapid inactivation with a time constant of 83 ms at 0 mV. Recovery from inactivation at -80 mV was rapid, with a time constant of 252 ms. The A-type current was blocked by 4-aminopyridine (4-AP) and was inhibited by flecainide, with an IC(50) of 35 microM. The voltage for half-activation was -26 mV, while the voltage of half-inactivation was -65 mV. There was significant activation and incomplete inactivation at potentials positive to -60 mV, which is suggestive of sustained current availability in this voltage range. Under current-clamp conditions, exposure to 4-AP or flecainide depolarized the membrane potential by 7-10 mV. In intact antral tissue preparations, flecainide depolarized the membrane potential between slow waves by 5 mV; changes in slow waves were not evident. The effect of flecainide was not abolished by inhibiting enteric neurotransmission or by blocking delayed rectifier and ATP-sensitive K(+) currents. Transcripts encoding Kv4 channels were detected in isolated antral myocytes by RT-PCR. Immunocytochemistry revealed intense Kv4.2- and Kv4.3-like immunoreactivity in antral myocytes. These data suggest that the A-type current in murine antral smooth muscle cells is likely to be due to Kv4 channels. This current contributes to the maintenance of negative resting membrane potentials.
A 型电流是在阈下电位起作用的快速失活钾电流。尚未有报道称 A 型电流出现在胃的相性肌中。我们使用传统电压钳技术来鉴定和表征从小鼠胃窦分离的心肌细胞中的 A 型电流。这些细胞中 A 型电流很强劲，在 0 mV 时峰值电流密度平均为 30 pA pF⁻¹。这些电流在 0 mV 时以 83 ms 的时间常数快速失活。在 -80 mV 时从失活状态恢复很快，时间常数为 252 ms。A 型电流被 4 - 氨基吡啶（4 - AP）阻断，并被氟卡尼抑制，半数抑制浓度（IC₅₀）为 35 μM。半激活电压为 -26 mV，而半失活电压为 -65 mV。在高于 -60 mV 的电位时存在显著激活和不完全失活，这表明在该电压范围内有持续的电流可用性。在电流钳条件下，暴露于 4 - AP 或氟卡尼会使膜电位去极化 7 - 10 mV。在完整的胃窦组织标本中，氟卡尼使慢波之间的膜电位去极化 5 mV；慢波变化不明显。抑制肠神经传递或阻断延迟整流钾电流和 ATP 敏感性钾电流并不能消除氟卡尼的作用。通过逆转录聚合酶链反应（RT - PCR）在分离的胃窦心肌细胞中检测到编码 Kv4 通道的转录本。免疫细胞化学显示胃窦心肌细胞中有强烈的 Kv4.2 和 Kv4.3 样免疫反应性。这些数据表明，小鼠胃窦平滑肌细胞中的 A 型电流可能归因于 Kv4 通道。这种电流有助于维持负的静息膜电位。
