Dhungel Kshitiz Upadhyay, Kim Tae Woon, Sharma Naveen, Bhattarai Janardhan Prasad, Park Seon Ah, Han Seong Kyu, Kim Chul Jin
Research Institute of Clinical Medicine, Chonbuk National University Medical School & Hospital, Jeonju, Korea.
Neurol Res. 2012 Jan;34(1):11-6. doi: 10.1179/1743132811Y.0000000049.
Magnesium has been known for treating vasospasm following subarachnoid hemorrhage. However, its action mechanism in cerebral vascular relaxation is not clear. Potassium channels play a pivotal role in the relaxation of smooth muscle cells. To investigate their role in magnesium-induced relaxation of basilar smooth muscle cells, we examined the effect of magnesium on potassium channels using the patch clamp technique on acutely isolated smooth muscle cells from rabbit basilar artery.
Fresh smooth muscle cells were isolated from the basilar artery by enzyme treatment. To identify which potassium channels are involved in the magnesium-induced currents, we used the potassium channel blockers tetraethylammonium (TEA), glibenclamide, apamin and iberiotoxin (IBX).
Magnesium (5 mM) increased the step pulse-induced outward K+ currents by 46% over control level (P < 0.01). The outward K+ current was decreased to 22% (P < 0.01) by TEA (10 mM), a non-specific K+ channel blocker, and to 60% of control level (P < 0.01) by IBX (0.1 μM,), a large-conductance Ca2+-activated K+ (BK) channel blocker, but was not inhibited by apamin (1 nM), a small-conductance Ca2+ -activated potassium (SK) channel blocker, or glibenclamide (3 mM), an adenosine triphosphate (ATP)-sensitive K+) channel blocker. Caffeine (3 mM) enhanced outward K+ currents. Magnesium-induced increase of outward K+ currents persisted in the presence of apamin. However, magnesium failed to increase the outward K+ currents in the presence of IBX.
These results demonstrate that BK channels are functionally expressed in rabbit basilar smooth muscle cells and suggest that BK channels may play a pivotal role in magnesium-induced relaxation.
镁已被用于治疗蛛网膜下腔出血后的血管痉挛。然而，其脑血管舒张的作用机制尚不清楚。钾通道在平滑肌细胞舒张中起关键作用。为研究它们在镁诱导的基底动脉平滑肌细胞舒张中的作用，我们采用膜片钳技术，对急性分离的兔基底动脉平滑肌细胞，研究了镁对钾通道的影响。
通过酶处理从基底动脉分离新鲜平滑肌细胞。为确定哪些钾通道参与镁诱导的电流，我们使用了钾通道阻滞剂四乙铵（TEA）、格列本脲、蜂毒明肽和iberiotoxin（IBX）。
镁（5 mM）使阶跃脉冲诱导的外向K+电流比对照水平增加46%（P < 0.01）。非特异性K+通道阻滞剂TEA（10 mM）使外向K+电流降至22%（P < 0.01），大电导Ca2+激活K+（BK）通道阻滞剂IBX（0.1 μM）使其降至对照水平的60%（P < 0.01），但小电导Ca2+激活钾（SK）通道阻滞剂蜂毒明肽（1 nM）或三磷酸腺苷（ATP）敏感性K+通道阻滞剂格列本脲（3 mM）对其无抑制作用。咖啡因（3 mM）增强外向K+电流。在存在蜂毒明肽的情况下，镁诱导的外向K+电流增加持续存在。然而，在存在IBX的情况下，镁未能增加外向K+电流。
这些结果表明BK通道在兔基底动脉平滑肌细胞中功能性表达，并提示BK通道可能在镁诱导的舒张中起关键作用。
