Gebremedhin D, Bonnet P, Greene A S, England S K, Rusch N J, Lombard J H, Harder D R
Department of Physiology, Medical College of Wisconsin, Milwaukee 53226.
Pflugers Arch. 1994 Oct;428(5-6):621-30. doi: 10.1007/BF00374586.
The cellular mechanisms mediating hypoxia-induced dilation of cerebral arteries have remained unknown, but may involve modulation of membrane ionic channels. The present study was designed to determine the effect of reduced partial pressure of O2, PO2, on the predominant K+ channel type recorded in cat cerebral arterial muscle cells, and on the diameter of pressurized cat cerebral arteries. A K(+)-selective single-channel current with a unitary slope conductance of 215 pS was recorded from excised inside-out patches of cat cerebral arterial muscle cells using symmetrical KCl (145 mM) solution. The open state probability (NPo) of this channel displayed a strong voltage dependence, was not affected by varying intracellular ATP concentration [(ATP]i) between 0 and 100 microM, but was significantly increased upon elevation of intracellular free Ca2+ concentration ([Ca2+]i). Low concentrations of external tetraethylammonium (0.1-3 mM) produced a concentration-dependent reduction of the unitary current amplitude of this channel. In cell-attached patches, where the resting membrane potential was set to zero with a high KCl solution, reduction of O2 from 21% to < 2% reversibly increased the NPo, mean open time, and event frequency of the Ca(2+)-sensitive, high-conductance single-channel K+ current recorded at a patch potential of +20 mV. A similar reduction in PO2 also produced a transient increase in the activity of the 215-pS K+ channel measured in excised inside-out patches bathed in symmetrical 145 mM KCl, an effect which was diminished, or not seen, during a second application of hypoxic superfusion. Hypoxia had no effect on [Ca2+]i or intracellular pH (pHi) of cat cerebral arterial muscle cells, as measured using Ca(2+)- or pH-sensitive fluorescent probes. Reduced PO2 caused a significant dilation of pressurized cerebral arterial segments, which was attenuated by pretreatment with 1 mM tetraethylammonium. These results suggest that reduced PO2 increases the activity of a high-conductance, Ca(2+)-sensitive K+ channel in cat cerebral arterial muscle cells, and that these effects are mediated by cytosolic events independent of changes in [Ca2+]i and pHi.
介导缺氧诱导脑动脉扩张的细胞机制尚不清楚，但可能涉及膜离子通道的调节。本研究旨在确定氧分压（PO2）降低对猫脑动脉肌细胞中记录到的主要钾通道类型以及对加压猫脑动脉直径的影响。使用对称氯化钾（145 mM）溶液，从猫脑动脉肌细胞的内向外膜片上记录到一种单位斜率电导为215 pS的钾选择性单通道电流。该通道的开放概率（NPo）表现出强烈的电压依赖性，在细胞内ATP浓度（[ATP]i）在0至100 microM之间变化时不受影响，但在细胞内游离钙浓度（[Ca2+]i）升高时显著增加。低浓度的细胞外四乙铵（0.1 - 3 mM）导致该通道的单位电流幅度呈浓度依赖性降低。在细胞贴附膜片中，用高氯化钾溶液将静息膜电位设置为零时，将氧从21%降至<2%可使在+20 mV膜电位下记录到的钙敏感、高电导单通道钾电流的NPo、平均开放时间和事件频率可逆性增加。PO2的类似降低也使在对称145 mM氯化钾中浸泡的内向外膜片中测量的215 pS钾通道活性短暂增加，在第二次缺氧灌注时这种效应减弱或未出现。如使用钙或pH敏感荧光探针所测，缺氧对猫脑动脉肌细胞的[Ca2+]i或细胞内pH（pHi）无影响。降低的PO2导致加压脑动脉段显著扩张，用1 mM四乙铵预处理可减弱这种扩张。这些结果表明，降低的PO2增加了猫脑动脉肌细胞中高电导、钙敏感钾通道的活性，并且这些效应由独立于[Ca2+]i和pHi变化的胞质事件介导。
