Aims: A sustained, single stretch of a cardiomyocyte activates a transient production of reactive oxygen species by membrane-located NADPH oxidase 2 (Nox2). This NoX2-dependent ROS (X-ROS) tunes cardiac Ca(2+) signalling by reversibly sensitizing sarcoplasmic reticulum Ca(2+) release channels. In contrast to static length changes, working heart cells are cyclically stretched and shortened in the living animal. Additionally, this stretch cycle is constantly varied by changes in the pre-load and heart rate. Thus, the objective of this study was (i) to characterize X-ROS signalling during stretch-shortening cycles and (ii) to evaluate how the amplitude (pre-load) and frequency (heart rate) of cell stretch affects X-ROS and Ca(2+) signalling.
Methods and results: Single adult rat cardiomyocytes were attached to MyoTak™-coated micro-rods and stretched, while ROS production and Ca(2+) signals were monitored optically. Although a sustained stretch led to only a transient burst of ROS, cyclic stretch-shortening cycles led to a steady-state elevation of ROS production. Importantly, this new redox state was graded by both the amplitude of stretch (3-15%) and cycle frequency (1-4 Hz). Elevated ROS production enhanced Ca(2+) signalling sensitivity as measured by the Ca(2+) spark rate.
Conclusion: The steady-state level of ROS production in a cardiomyocyte is graded by the amplitude and frequency of cell stretch. Thus, mechanical changes that depend on the pre-load and heart rate regulate a dynamic redox balance that tunes cellular Ca(2+) signalling.