Rho-mediated suppression of KDR current in cerebral arteries

Bibliography: p. 115-13

Rho-kinase-mediated suppression of KDR current in cerebral arteries requires an intact actin cytoskeleton

This study examined the role of the actin cytoskeleton in Rho-kinase-mediated suppression of the delayed-rectifier K+ (KDR) current in cerebral arteries. Myocytes from rat cerebral arteries were enzymatically isolated, and whole cell KDR currents were monitored using conventional patch-clamp electrophysiology. At +40 mV, the KDR current averaged 19.8 ± 1.6 pA/pF (mean ± SE) and was potently inhibited by UTP (3 × 10−5 M). This suppression was observed to depend on Rho signaling and was abolished by the Rho-kinase inhibitors H-1152 (3 × 10−7 M) and Y-27632 (3 × 10−5 M). Rho-kinase was also found to concomitantly facilitate actin polymerization in response to UTP. We therefore examined whether actin dynamics played a role in the ability of Rho-kinase to suppress KDR current and found that actin disruption using either cytochalasin D (1 × 10−5 M) or latrunculin A (1 × 10−8 M) prevented current modulation. Consistent with our electrophysiological observations, both Rho-kinase inhibition and actin disruption significantly attenuated UTP-induced depolarization and constriction of cerebral arteries. We propose that UTP initiates Rho-kinase-mediated remodeling of the actin cytoskeleton and consequently suppresses the KDR current, thereby facilitating the depolarization and constriction of cerebral arteries

KIR channels function as electrical amplifiers in rat vascular smooth muscle

Strong inward rectifying K+ (KIR) channels have been observed in vascular smooth muscle and can display negative slope conductance. In principle, this biophysical characteristic could enable KIR channels to ‘amplify’ responses initiated by other K+ conductances. To test this, we have characterized the diversity of smooth muscle KIR properties in resistance arteries, confirmed the presence of negative slope conductance and then determined whether KIR inhibition alters the responsiveness of middle cerebral, coronary septal and third-order mesenteric arteries to K+ channel activators. Our initial characterization revealed that smooth muscle KIR channels were highly expressed in cerebral and coronary, but not mesenteric arteries. These channels comprised KIR2.1 and 2.2 subunits and electrophysiological recordings demonstrated that they display negative slope conductance. Computational modelling predicted that a KIR-like current could amplify the hyperpolarization and dilatation initiated by a vascular K+ conductance. This prediction was consistent with experimental observations which showed that 30 μm Ba2+ attenuated the ability of K+ channel activators to dilate cerebral and coronary arteries. This attenuation was absent in mesenteric arteries where smooth muscle KIR channels were poorly expressed. In summary, smooth muscle KIR expression varies among resistance arteries and when channel are expressed, their negative slope conductance amplifies responses initiated by smooth muscle and endothelial K+ conductances. These findings highlight the fact that the subtle biophysical properties of KIR have a substantive, albeit indirect, role in enabling agonists to alter the electrical state of a multilayered artery