Heparin-binding EGF-like growth factor mediates oxyhemoglobin-induced suppression of voltage-dependent potassium channels in rabbit cerebral artery myocytes

Abstract

Koide M, Penar PL, Tranmer BI, Wellman GC. Heparinbinding EGF-like growth factor mediates oxyhemoglobin-induced suppression of voltage-dependent potassium channels in rabbit cerebral artery myocytes. Am J Physiol Heart Circ Physiol 293: H1750-H1759, 2007. First published June 8, 2007; doi:10.1152/ajpheart.00443.2007 can suppress voltage-dependent K ϩ channel (KV) currents through protein tyrosine kinase activation, which may contribute to cerebral vasospasm following subarachnoid hemorrhage. Here we have tested the hypothesis that shedding of heparin-binding EGF-like growth factor (HB-EGF) and the resulting activation of the tyrosine kinase EGF receptor (EGFR) underlie OxyHb-induced K V channel suppression in the cerebral vasculature. With the use of the conventional whole cell patch-clamp technique, two EGFR ligands, EGF and HB-EGF, were found to mimic OxyHb-induced KV suppression in rabbit cerebral artery myocytes. KV current suppression by OxyHb or EGF ligands was eliminated by a specific EGFR inhibitor, AG-1478, but was unaffected by PKC inhibition. that specifically interfere with HB-EGF signaling eliminated OxyHbinduced K V suppression, suggesting that HB-EGF is the EGFR ligand involved in this pathway. HB-EGF exists as a precursor protein that, when cleaved by matrix metalloproteases (MMPs), causes EGFR activation. MMP activation was detected in OxyHb-treated arteries by gelatin zymography. Furthermore, the MMP inhibitor (GM-6001) abolished OxyHb-induced KV current suppression. We also observed KV current suppression due to EGFR activation in human cerebral artery myocytes. In conclusion, these data demonstrate that OxyHb induces MMP activation, causing HB-EGF shedding and enhanced EGFR activity, ultimately leading to KV channel suppression. We propose that EGFR-mediated KV suppression contributes to vascular pathologies, such as cerebral vasospasm, and may play a more widespread role in the regulation of regional blood flow and peripheral resistance. vascular smooth muscle; growth factors; subarachnoid hemorrhage; tyrosine kinase VOLTAGE-DEPENDENT DELAYED rectifier K ϩ (K V ) channels play an important role in the maintenance of vascular smooth muscle membrane potential and the regulation of arterial diameter (13,35). A reduction in K V channel activity and/or a decrease in K V channel expression in vascular smooth muscle would promote membrane potential depolarization, increased Ca 2ϩ influx via voltage-dependent Ca 2ϩ channels, and vasoconstriction (27). Decreased K V currents have been linked to a number of endogenous and exogenous vasoconstrictors, and K V current suppression has been implicated in systemic and pulmonary hypertension, as well as cerebral vasospasm following aneurysmal subarachnoid hemorrhage (SAH) (22,24,42,49). A large body of evidence suggests that the blood component oxyhemoglobin (OxyHb) contributes to SAH-induced vasoconstriction (3), and our laboratory has recently reported that OxyHb suppresses K V currents in cerebral artery myocytes via a mechanism involving enhanced prote...

Fundamental increase in pressure-dependent constriction of brain parenchymal arterioles from subarachnoid hemorrhage model rats due to membrane depolarization

“…Numerous studies have suggested that substances within blood may lead to membrane potential depolarization of cerebral artery myocytes via suppression of K ϩ channel activity (13,20,55). For example, using rabbit pial arteries, our laboratory has shown (28,35) that acute exposure of vascular smooth muscle to the blood component oxyhemoglobin can cause internalization of K V 1.5 via a mechanism involving protein tyrosine kinase activation. Others have additionally demonstrated that mRNA and protein levels of K V 2.2 channels were decreased in basilar arteries from a canine SAH model (31).…”

Inversion of neurovascular coupling by subarachnoid blood depends on large-conductance Ca 2+ -activated K + (BK) channels

“…For example, pressurized parenchymal arterioles isolated from SAH animals exhibit depolarization of smooth muscle membrane potential and enhanced constriction in vitro (14). Direct vasoconstrictor effects of blood components such as oxyhemoglobin include suppression of smooth muscle K + channels (44)(45)(46), up-regulation of voltagedependent Ca 2+ channels (47) or transient receptor potential channels (48), and scavenging of nitric oxide (49).…”

“…Parenchymal arteriolar myocytes were isolated enzymatically using a previously described protocol (45). Cells used for patch-clamp studies were kept on ice for up to 6 h. Membrane K + currents were measured with conventional whole-cell patch-clamp electrophysiology using a holding potential of −70 mV.…”

Reduced Ca2+ Spark Activity after Subarachnoid Hemorrhage Disables BK Channel Control of Cerebral Artery Tone

“…Membrane potential depolarization caused by a decrease in Ca 2+ spark-induced transient BK currents would be predicted to cause an increase in the open-state probability of VDCCs and combined with enhanced VDCC expression would increase global cytosolic Ca 2+ leading to enhanced contraction of cerebral artery myocytes. Additional mechanisms such as decreased voltage-dependent potassium (K V ) channel expression (Jahromi et al, 2008a) and activity (Ishiguro et al, 2006;Koide et al, 2007;Quan and Sobey, 2000) and increased protein kinase C activity (Nishizawa et al, 2000) are also likely to contribute to enhanced cerebral artery constriction after SAH.…”

“…The threshold for current peak detection was set at two and half times the single-channel amplitude of BK channel (e.g., 5.0 pA at À40 mV) (Perez et al, 2001). Single-Channel BK Current Recordings: The BK singlechannel currents were recorded in excised inside-out membrane patches at RT (Perez et al, 2001 Whole-cell K + currents were measured using the conventional whole-cell configuration of the patch-clamp technique (Koide et al, 2007). The composition of bath solution was the same as the 6 mmol/L K + HEPES-PSS described above.…”