TNF- dilates cerebral arteries via NAD(P)H oxidase-dependent Ca spark activation

Cheranov, Sergey Y., and Jonathan H. Jaggar. TNFdilates cerebral arteries via NAD(P)H oxidase-dependent Ca spark activation. Am J Physiol Cell Physiol 290: C964–C971, 2006. First published November 2, 2005; doi:10.1152/ajpcell.00499.2005.—Expression of TNF, a pleiotropic cytokine, is elevated during stroke and cerebral ischemia. TNFregulates arterial diameter, although mechanisms mediating this effect are unclear. In the present study, we tested the hypothesis that TNFregulates the diameter of resistancesized ( 150m diameter) cerebral arteries by modulating local and global intracellular Ca signals in smooth muscle cells. Laserscanning confocal imaging revealed that TNFincreased Ca spark and Ca wave frequency but reduced global intracellular Ca concentration ([Ca ]i) in smooth muscle cells of intact arteries. TNFelevated reactive oxygen species (ROS) in smooth muscle cells of intact arteries, and this increase was prevented by apocynin or diphenyleneiodonium (DPI), both of which are NAD(P)H oxidase blockers, but was unaffected by inhibitors of other ROS-generating enzymes. In voltage-clamped ( 40 mV) cells, TNFincreased the frequency and amplitude of Ca spark-induced, large-conductance, Ca -activated K (KCa) channel transients 1.7and 1.4-fold, respectively. TNF-induced transient KCa current activation was reversed by apocynin or by Mn(III)tetrakis(1-methyl-4-pyridyl)porphyrin (MnTMPyP), a membrane-permeant antioxidant, and was prevented by intracellular dialysis of catalase. TNFinduced reversible and similar amplitude dilations in either endothelium-intact or endothelium-denuded pressurized (60 mmHg) cerebral arteries. MnTMPyP, thapsigargin, a sarcoplasmic reticulum Ca -ATPase blocker that inhibits Ca sparks, and iberiotoxin, a KCa channel blocker, reduced TNF-induced vasodilations to between 15 and 33% of control. In summary, our data indicate that TNFactivates NAD(P)H oxidase, resulting in an increase in intracellular H2O2 that stimulates Ca sparks and transient KCa currents, leading to a reduction in global [Ca ]i, and vasodilation. cerebrovascular circulation; ryanodine-sensitive Ca release channel; Ca -activated K channel; reactive oxygen species; vasodilation