H 2 O 2 Is the Transferrable Factor Mediating Flow-Induced Dilation in Human Coronary Arterioles

Abstract

Rationale:: Endothelial derived hydrogen peroxide (H ₂ O ₂ ) is a necessary component of the pathway regulating flow-mediated dilation (FMD) in human coronary arterioles (HCAs). However, H ₂ O ₂ has never been shown to be the endothelium-dependent transferrable hyperpolarization factor (EDHF) in response to shear stress. Objective:: We examined the hypothesis that H ₂ O ₂ serves as the EDHF in HCAs to shear stress. Methods and Results:: Two HCAs were cannulated in series (a donor intact vessel upstream and endothelium-denuded detector vessel downstream). Diameter changes to flow were examined in the absence and presence of polyethylene glycol catalase (PEG-CAT). The open state probability of large conductance Ca ²⁺ -activated K ⁺ (BK _Ca ) channels in smooth muscle cells downstream from the perfusate from an endothelium-intact arteriole was examined by patch clamping. In some experiments, a cyanogen bromide–activated resin column bound with CAT was used to remove H ₂ O ₂ from the donor vessel. When flow proceeds from donor to detector, both vessels dilate (donor:68±7%; detector: 45±11%). With flow in the opposite direction, only the donor vessel dilates. PEG-CAT contacting only the detector vessel blocked FMD in that vessel (6±4%) but not in donor vessel (61±13%). Paxilline inhibited dilation of endothelium-denuded HCAs to H ₂ O ₂ . Effluent from donor vessels elicited K ⁺ channel opening in an iberiotoxin- or PEG-CAT–sensitive fashion in cell-attached patches but had little effect on channel opening on inside-out patches. Vasodilation of detector vessels was diminished when exposed to effluent from CAT-column. Conclusions:: Flow induced endothelial production of H ₂ O ₂ , which acts as the transferrable EDHF activating BK _Ca channels on the smooth muscle cells.