Ishiguro Masanori, Morielli Anthony D, Zvarova Katarina, Tranmer Bruce I, Penar Paul L, Wellman George C
Department of Pharmacology, Division of Neurological Surgery, University of Vermont College of Medicine, Burlington 05405-0068, USA.
Circ Res. 2006 Nov 24;99(11):1252-60. doi: 10.1161/01.RES.0000250821.32324.e1. Epub 2006 Oct 26.
Cerebral vasospasm following aneurysmal subarachnoid hemorrhage (SAH) has devastating consequences. Oxyhemoglobin (oxyhb) has been implicated in SAH-induced cerebral vasospasm as it causes cerebral artery constriction and increases tyrosine kinase activity. Voltage-dependent, Ca(2+)-selective and K(+)-selective ion channels play an important role in the regulation of cerebral artery diameter and represent potential targets of oxyhb. Here we provide novel evidence that oxyhb selectively decreases 4-aminopyridine sensitive, voltage-dependent K(+) channel (K(v)) currents by approximately 30% in myocytes isolated from rabbit cerebral arteries but did not directly alter the activity of voltage-dependent Ca(2+) channels or large conductance Ca(2+)-activated (BK) channels. A combination of tyrosine kinase inhibitors (tyrphostin AG1478, tyrphostin A23, tyrphostin A25, genistein) abolished both oxyhb-induced suppression of K(v) channel currents and oxyhb-induced constriction of isolated cerebral arteries. The K(v) channel blocker 4-aminopyridine also inhibited oxyhb-induced cerebral artery constriction. The observed oxyhb-induced decrease in K(v) channel activity could represent either channel block, or a decrease in K(v) channel density on the plasma membrane. To explore whether oxyhb altered trafficking of K(v) channels to the plasma membrane, we used an antibody generated against an extracellular epitope of K(v)1.5 channels. In the presence of oxyhb, staining of K(v)1.5 on the plasma membrane surface was markedly reduced. Furthermore, oxyhb caused a loss of spatial distinction between staining with K(v)1.5 and the general anti-phosphotyrosine antibody PY-102. We propose that oxyhb-induced suppression of K(v) currents occurs via a mechanism involving enhanced tyrosine kinase activity and channel endocytosis. This novel mechanism may contribute to oxyhb-induced cerebral artery constriction following SAH.
动脉瘤性蛛网膜下腔出血（SAH）后的脑血管痉挛具有毁灭性后果。氧合血红蛋白（oxyhb）与SAH诱导的脑血管痉挛有关，因为它会导致脑动脉收缩并增加酪氨酸激酶活性。电压依赖性、Ca(2+)选择性和K(+)选择性离子通道在脑动脉直径的调节中起重要作用，并且是oxyhb的潜在靶点。在此，我们提供了新的证据，即oxyhb可使从兔脑动脉分离的心肌细胞中4-氨基吡啶敏感的电压依赖性K(+)通道（K(v)）电流选择性降低约30%，但不会直接改变电压依赖性Ca(2+)通道或大电导Ca(2+)-激活（BK）通道的活性。酪氨酸激酶抑制剂（ tyrphostin AG1478、tyrphostin A23、tyrphostin A25、染料木黄酮）的组合消除了oxyhb诱导的K(v)通道电流抑制和oxyhb诱导的离体脑动脉收缩。K(v)通道阻滞剂4-氨基吡啶也抑制了oxyhb诱导的脑动脉收缩。观察到的oxyhb诱导的K(v)通道活性降低可能代表通道阻滞，或质膜上K(v)通道密度的降低。为了探究oxyhb是否改变了K(v)通道向质膜的转运，我们使用了针对K(v)1.5通道细胞外表位产生的抗体。在oxyhb存在的情况下，质膜表面K(v)1.5的染色明显减少。此外，oxyhb导致K(v)1.5染色与一般抗磷酸酪氨酸抗体PY-102之间的空间区分丧失。我们提出，oxyhb诱导的K(v)电流抑制是通过一种涉及增强酪氨酸激酶活性和通道内吞作用的机制发生的。这种新机制可能导致SAH后oxyhb诱导的脑动脉收缩。
