Acute and chronic hypoxic regulation of ion channels is involved in both cell physiology and pathology. Voltage-dependent Na+ channels play a dominant role in the upstroke of the action potential in excitable cells, while non-inactivating (persistent or sustained) Na+ currents contribute to action potential shape and duration. In cardiac myocytes, hypoxic augmentation of persistent Na+ currents has been proposed to underlie cardiac arrhythmias via prolonging action potential duration. Here, we demonstrate that acute hypoxia (PO2 20 mmHg) augmented persistent Na+ currents in HEK293 cells stably expressing human Na(v)1.5 alpha subunits. Hypoxia also inhibited peak Na+ currents in a voltage-dependent manner, and the kinetics of activation and inactivation of Na+ currents were significantly slowed during hypoxia. We further demonstrate that exposure to chronic hypoxia (6% O-2 for 24 h) augmented peak Na+ channel current, which given the exogenous promoter driving expression of the channel occurs most probably via a post-transcriptional mechanism. These effects of acute and chronic hypoxia likely play an arrhythmogenic role during both short- and long-term hypoxic/ischaemic episodes. The HEK293 expression system provides a useful paradigm in which to examine the mechanisms of O-2 sensing by the Na+ channel. (C) 2004 Elsevier Inc. All rights reserved.