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 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 ≈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.