Flow-dependent increase of ICAM-1 on saphenous vein endothelium is sensitive to apamin

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Abstract
The potassium channel blocker tetraethylammonium blocks the flow-induced increase in endothelial ICAM-1. We have investigated the subtype of potassium channel that modulates flow-induced increased expression of ICAM-1 on saphenous vein endothelium. Cultured human saphenous vein endothelial cells (HSVECs) or intact saphenous veins were perfused at fixed low and high flows in a laminar shear chamber or flow rig, respectively, in the presence or absence of potassium channel blockers. Expression of K+ channels and endothelial ICAM-1 was measured by real-time polymerase chain reaction and/or immunoassays. In HSVECs, the application of 0.8 N/m2 (8 dyn/cm2) shear stress resulted in a two- to fourfold increase in cellular ICAM-1 within 6 h ( P < 0.001). In intact vein a similar shear stress, with pulsatile arterial pressure, resulted in a twofold increase in endothelial ICAM-1/CD31 staining area within 1.5 h ( P < 0.001). Both increases in ICAM-1 were blocked by inclusion of 100 nM apamin in the vein perfusate, whereas other K+ channel blockers were less effective. Two subtypes of small conductance Ca2+-activated K+ channel (selectively blocked by apamin) were expressed in HSVECs and vein endothelium (SK3>SK2). Apamin blocked the upregulation of ICAM-1 on saphenous vein endothelium in response to increased flow to implicate small conductance Ca2+-activated K+ channels in shear stress/flow-mediated signaling pathways.