Kim Donghee, Cavanaugh Eric J, Kim Insook, Carroll John L
Department of Physiology and Biophysics, Rosalind Franklin University of Medicine and Science, The Chicago Medical School, 3333 Green Bay Road, North Chicago, IL 60064, USA.
J Physiol. 2009 Jun 15;587(Pt 12):2963-75. doi: 10.1113/jphysiol.2009.171181. Epub 2009 Apr 29.
Carotid body (CB) glomus cells from rat express a TASK-like background K+ channel that is believed to play a critical role in the regulation of excitability and hypoxia-induced increase in respiration. Here we studied the kinetic behaviour of single channel openings from rat CB cells to determine the molecular identity of the 'TASK-like' K+ channels. In outside-out patches, the TASK-like background K+ channel in CB cells was inhibited >90% by a reduction of pH(o) from 7.3 to 5.8. In cell-attached patches with 140 mM KCl and 1 mM Mg2+ in the bath and pipette solutions, two main open levels with conductance levels of approximately 14 pS and approximately 32 pS were recorded at a membrane potential of -60 mV. The K+ channels showed kinetic properties similar to TASK-1 (approximately 14 pS), TASK-3 (approximately 32 pS) and TASK-1/3 heteromer (approximately 32 pS). The presence of three TASK isoforms was tested by reducing Mg2+ to approximately 0 mM, which had no effect on the conductance of TASK-1, but increased those of TASK-1/3 and TASK-3 to 42 pS and 74 pS, respectively. In CB cells, the reduction of Mg2+ to approximately 0 mM also caused the appearance of approximately 42 pS (TASK-1/3-like) and approximately 74 pS (TASK-3-like) channels, in addition to the approximately 14 pS (TASK-1-like) channel. The 42 pS channel was the most abundant, contributing approximately 75% of the current produced by TASK-like channels. Ruthenium red (5 microM) had no effect on TASK-1 and TASK-1/3, but inhibited TASK-3 by 87%. In CB cells, ruthenium red caused approximately 12% inhibition of TASK-like activity. Methanandamide reduced the activity of all three TASKs by 80-90%, and that of TASK-like channels in CB cell also by approximately 80%. In CB cells, hypoxia caused inhibition of TASK-like channels, including TASK-1/3-like channels. These results show that TASK-1, TASK-1/3 and TASK-3 are all functionally expressed in isolated CB cells, and that the TASK-1/3 heteromer provides the major part of the oxygen-sensitive TASK-like background K+ conductance.
大鼠的颈动脉体（CB）球细胞表达一种类似TASK的背景钾通道，据信该通道在兴奋性调节和低氧诱导的呼吸增强中起关键作用。在此，我们研究了大鼠CB细胞单通道开放的动力学行为，以确定“类似TASK”钾通道的分子身份。在外侧向外膜片中，将细胞外pH值从7.3降至5.8可使CB细胞中类似TASK的背景钾通道受到>90%的抑制。在浴液和微管溶液中含有140 mM KCl和1 mM Mg2+的细胞贴附膜片中，在膜电位为-60 mV时记录到两个主要的开放水平，电导水平分别约为14 pS和约32 pS。这些钾通道表现出与TASK-1（约14 pS）、TASK-3（约32 pS）和TASK-1/3异源二聚体（约32 pS）相似的动力学特性。通过将细胞外镁离子浓度Mg2+降至约0 mM来测试三种TASK亚型的存在情况，这对TASK-1的电导没有影响，但分别将TASK-1/3和TASK-3的电导增加到42 pS和74 pS。在CB细胞中，将Mg2+降至约0 mM还导致除了约14 pS（类似TASK-1）通道外，出现了约42 pS（类似TASK-1/3）和约74 pS（类似TASK-3）的通道。42 pS的通道最为丰富，占类似TASK通道产生电流的约75%。钌红（5 microM）对TASK-1和TASK-1/3没有影响，但可使TASK-3受到87%的抑制。在CB细胞中，钌红使类似TASK的活性受到约12%的抑制。甲硫酰胺使所有三种TASK的活性降低80-90%，也使CB细胞中类似TASK通道的活性降低约80%。在CB细胞中，低氧会抑制类似TASK的通道，包括类似TASK-1/3的通道。这些结果表明，TASK-1、TASK-1/3和TASK-3在分离的CB细胞中均有功能表达，并且TASK-1/3异源二聚体提供了对氧敏感的类似TASK背景钾电导的主要部分。
