视网膜小动脉平滑肌细胞中的A型钾电流。
A-type potassium current in retinal arteriolar smooth muscle cells.
作者信息
McGahon Mary K, Dawicki Jennine M, Scholfield C Norman, McGeown J Graham, Curtis Tim M
机构信息
Centre of Vision Sciences, The Queen's University of Belfast, Institute of Clinical Sciences, The Royal Victoria Hospital, Grosvenor Road, Belfast BT12 6BA, Northern Ireland.
出版信息
Invest Ophthalmol Vis Sci. 2005 Sep;46(9):3281-7. doi: 10.1167/iovs.04-1465.
PURPOSE
By their control of membrane potential and intracellular free Ca(2+) (Ca(2+)), K(+) currents are pivotal in the regulation of arterial smooth muscle tone. The goal of the present study was to identify and characterize the A-type K(+) current in retinal microvascular smooth muscle (MVSM) and to examine its role in modulating membrane potential and cellular contractility.
METHODS
Whole-cell perforated patch-clamp recordings were made from MVSM cells within intact isolated arteriolar segments. Before patch-clamping, retinal arterioles were anchored in the physiological recording bath and perfused with an enzyme cocktail to remove surface basal lamina and to uncouple electrically the endothelial cells from the overlying MVSM cells.
RESULTS
K(+) currents were activated by depolarizing steps from -80 to +100 mV in 20-mV increments. A dominant, noninactivating current was elicited by depolarization to potentials positive of -50 mV. Inhibition of this current by 100 nM of the Ca(2+)-activated K(+) channel blocker, Penitrem A, revealed a rapidly inactivating K(+) current that resembled an A-type current. The A-type current was insensitive to tetraethylammonium (TEA) at 1 mM, but was partially suppressed by higher concentrations (10 mM). 4-Aminopyridine (10 mM; 4-AP) completely blocked the A-type current. The 4-AP-sensitive transient current was activated at a potential of -60 mV with peak current densities averaging 29.7 +/- 5.68 pA/pF at +60 mV. The voltage of half-inactivation was -28.3 +/- 1.9 mV, and the time constant for recovery from inactivation at +60 mV was 118.7 +/- 7.9 ms. Under current-clamp conditions 4-AP depolarized the membrane potential by approximately 3 to 4 mV and triggered small contractions and relaxations of individual MVSM cells within the walls of the arterioles.
CONCLUSIONS
A-type current is the major voltage-dependent K(+) current in retinal MVSM and appears to play a physiological role in suppressing cell excitability and contractility.
目的
钾离子电流通过控制膜电位和细胞内游离钙离子（[Ca²⁺]i），在调节动脉平滑肌张力中起关键作用。本研究的目的是鉴定和表征视网膜微血管平滑肌（MVSM）中的A型钾离子电流，并研究其在调节膜电位和细胞收缩性中的作用。
方法
采用全细胞膜片钳穿孔膜片钳记录完整分离的小动脉段内的MVSM细胞。在进行膜片钳记录之前，将视网膜小动脉固定在生理记录浴槽中，并用酶混合液灌注以去除表面基膜，并使内皮细胞与上方的MVSM细胞电分离。
结果
钾离子电流通过以20 mV步长从 -80 mV去极化到 +100 mV来激活。去极化到 -50 mV以上的电位会引发一种占主导地位的、非失活电流。用100 nM的钙激活钾离子通道阻滞剂Penitrem A抑制该电流，揭示出一种快速失活的钾离子电流，类似于A型电流。A型电流对1 mM的四乙铵（TEA）不敏感，但在较高浓度（10 mM）时会部分受到抑制。4-氨基吡啶（10 mM；4-AP）完全阻断A型电流。4-AP敏感的瞬态电流在 -60 mV的电位下被激活，在 +60 mV时的峰值电流密度平均为29.7±5.68 pA/pF。半失活电压为 -28.3±1.9 mV，在 +60 mV时从失活恢复的时间常数为118.7±7.9 ms。在电流钳条件下，4-AP使膜电位去极化约3至4 mV，并引发小动脉壁内单个MVSM细胞的小收缩和舒张。
结论
A型电流是视网膜MVSM中主要的电压依赖性钾离子电流，似乎在抑制细胞兴奋性和收缩性中发挥生理作用。
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