Adaptation of Human Endothelial Cells to Physiological Oxygen Levels Alters Basal and Nitric Oxide-Stimulated K + Channel Activity

Endothelial cells (EC) play a critical role in vascular homeostasis, and their function is influenced by oxygen tension. This study investigates long-term effects of EC culture under physiological oxygen tension on their basal and nitric oxide (NO)-modulated K⁺ channel activities. Electrophysiological experiments demonstrated for the first time that human umbilical vein EC (HUVEC) exhibit larger basal K⁺ outward and smaller inward currents under normoxic (5kPa) compared to hyperoxic (18kPa) O2 levels. Outward currents were only potentiated under hyperoxic conditions by NO. Human cerebral microvascular EC (hCMEC/D3) showed larger outward currents under normoxia which were further potentiated by NO. Protein expression of Kir6.1, KCa3.1, KCa1.1 and KCa2.3 channels was unaffected by ambient O2, suggesting that observed changes in K+ currents in both EC types were due to ion channel modulation. In HUVEC, changes in half-activation voltage and hyperpolarized membrane potentials were detected only under hyperoxic conditions following NO exposure, with both cell types exhibiting altered current activation kinetics of outward and inward currents between culture conditions. Together, we report novel insights into the modulation of K+ channels in EC, with implications for regulation of vascular tone and the design and use of experimental models in vitro for high throughput drug discovery and clinical translation.