Shear stress increases expression of a KATP channel in rat and bovine pulmonary vascular endothelial cells

We have shown previously that acute ischemia leads to depolarization of pulmonary microvascular endothelial cells that is prevented with cromakalim, suggesting the presence of ATP-sensitive K+ (K-ATP) channels in these cells. Thus K-ATP channel expression and activity were evaluated in rat pulmonary microvascular endothelial cells (RPMVEC) by whole cell current measurements, dot blot (mRNA), and immunoblot (protein) for the inwardly rectifying K+ channel (KIR) 6.2 subunit and fluorescent ligand binding for the sulfonylurea receptor (SUR). Low-level expression of a K-ATP channel was detected in endothelial cells in routine (static) culture and led us to examine whether its expression is inducible when endothelial cells are adapted to flow. Channel expression (mRNA and both K(IR)6.2 and SUR proteins) and inwardly rectified membrane current by patch clamp increased significantly when RPMVEC were adapted to flow at 10 dyn/cm(2) for 24 h in either a parallel plate flow chamber or an artificial capillary system. Induction of the K-ATP channel with flow adaptation was also observed in bovine pulmonary artery endothelial cells. Flow-adapted but not static RPMVEC showed cellular plasma membrane depolarization upon stop of flow that was inhibited by a K-ATP channel opener and prevented by addition of cycloheximide to the medium during the flow adaptation period. These studies indicate the induction of K-ATP channels by flow adaptation in pulmonary endothelium and that the expression and activity of this channel are essential for the endothelial cell membrane depolarization response with acute decrease in shear stress.