# Physiological oxygen levels reset K+ channel activity in human vascular endothelial cells

## TL;DR

This study shows that human vascular endothelial cells respond differently to normal oxygen levels compared to high oxygen levels, affecting potassium channel activity and nitric oxide responses.

## Contribution

The first study to show how physiological oxygen levels modulate potassium channel activity and nitric oxide responsiveness in human vascular endothelial cells.

## Key findings

- Human umbilical vein EC show larger outward and smaller inward K+ currents under 5 kPa O2.
- NO modulates K+ currents differently under physiological and hyperoxic conditions.
- Physiological O2 tension alters the electrophysiological phenotype of human EC via K+ channel modulation.

## Abstract

Human endothelial cells (EC) play a critical role in vascular homeostasis and their function is influenced by oxygen tension. This study investigates for the first time the effects of long-term adaptation (5 days) of two major EC types to physiological oxygen tension (5 kPa) on basal and nitric oxide (NO)-modulated K+ channel activities. Whole-cell patch clamp experiments demonstrate that human umbilical vein EC (HUVEC) exhibit larger basal K+ outward and smaller inward currents under 5 kPa O2 compared to standard hyperoxic (18 kPa) culture conditions. Outward currents were potentiated by NO only under hyperoxia. Human cerebral microvascular EC (hCMEC/D3) showed larger outward currents under 5 kPa O2 which were further potentiated by NO. Pharmacological isolation of different K+ currents using tetraethylammonium, TRAM-34 and apamin revealed differential effects in EC adapted to 5 kPa or 18 kPa O2. Under 5 kPa O2, both cell types show greater contributions of TEA-sensitive currents and in addition hCMEC/D3 cells exhibit higher proportions of TRAM-34 and apamin-sensitive currents under 5 kPa O2. 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. Notably, expression of KCa3.1, KCa1.1, KCa2.3 and Kir6.1 channels was unaffected by O2, suggesting that changes in whole-cell currents in both EC types were due to channel modulation. Thus, our findings reveal that physiological O2 tension shapes the electrophysiological phenotype of human EC by modulating K+ channel function and NO responsiveness. The novel insights into the modulation of EC K+ channels by O2 has implications for the regulation of vascular tone and design and use of experimental models in vitro for high throughput drug discovery and clinical translation.

Image 1

•Adaptation to 5 kPa O2 enhances basal whole-cell currents in HUVEC and hCMEC/D3.•NO augments currents in HUVEC and hCMEC/D3 only in hyperoxia and physioxia, respectively.•BK, SK and IK channels contribute differentially to whole-cell currents.•Critical importance of physioxia in vitro studies to inform vascular modeling and drug screening.

Adaptation to 5 kPa O2 enhances basal whole-cell currents in HUVEC and hCMEC/D3.

NO augments currents in HUVEC and hCMEC/D3 only in hyperoxia and physioxia, respectively.

BK, SK and IK channels contribute differentially to whole-cell currents.

Critical importance of physioxia in vitro studies to inform vascular modeling and drug screening.