Oxyhemoglobin-induced suppression of voltage-dependent K+ channels in cerebral arteries by enhanced tyrosine kinase activity

Abstract

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-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 (Kv) currents by ≈30% in myocytes isolated from rabbit cerebral arteries but did not directly alter the activity of voltage-dependent Ca channels or large conductance Ca-activated (BK) channels. A combination of tyrosine kinase inhibitors (tyrphostin AG1478, tyrphostin A23, tyrphostin A25, genistein) abolished both oxyhb-induced suppression of Kv channel currents and oxyhb-induced constriction of isolated cerebral arteries. The Kv channel blocker 4-aminopyridine also inhibited oxyhb-induced cerebral artery constriction. The observed oxyhb-induced decrease in Kv channel activity could represent either channel block, or a decrease in Kv channel density on the plasma membrane. To explore whether oxyhb altered trafficking of Kv channels to the plasma membrane, we used an antibody generated against an extracellular epitope of Kv1.5 channels. In the presence of oxyhb, staining of Kv1.5 on the plasma membrane surface was markedly reduced. Furthermore, oxyhb caused a loss of spatial distinction between staining with Kv1.5 and the general anti-phosphotyrosine antibody PY-102. We propose that oxyhb-induced suppression of Kv 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. © 2006 American Heart Association, Inc.