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Free Radical Biology and Medicine


The plasma membrane calcium ATPase (PMCA) is a high affinity ion transporter that pumps Ca2+ out of cells to maintain optimal intracellular Ca2+ levels essential for cell function. Previous studies from our laboratory have shown the PMCA to be uniquely sensitive to oxidative stress. Exposure to reactive oxygen species (ROS) of physiological relevance caused dramatic inactivation, aggregation, and proteolytic degradation of the protein. Type 2 diabetes, an extremely prevalent metabolic pathophysiological condition is associated with oxidative stress. Cellular damage caused by ROS exacerbates diabetes and paves the way for the development of other pathological conditions such as cardiovascular disease and neurodegenerative disorders. There is a significant body of literature outlining mechanisms underlying the influx of Ca2+ through calcium channels, critical for insulin release by the pancreatic beta cells (PBCs). However, the mechanisms that remove excess intracellular Ca2+ and bring it back to baseline levels have not been well studied. The goal of the current research was to determine the effects of oxidative stress on the PMCA in PBCs. Cultured cells were treated with 1- 200 μM of H2O2 for 24 hours. PMCA activity was measured by monitoring Ca2+ - dependent ATP hydrolysis and PMCA protein levels were determined by immunoblotting. Exposure of cells to H2O2 caused a biphasic effect on PMCA activity with a significant stimulation observed at low concentrations of H2O2 and inactivation observed at high concentrations. Live cell Ca2+ imaging showed a significant increase in intracellular Ca2+ levels upon exposure to H2O2. Immunoblot analyses showed evidence of PMCA aggregation and fragmentation suggesting structural changes in PMCA. These results indicate a significant impact of oxidative stress on the Ca2+ clearance machinery of PBCs establishing a direct link between PMCA and the pathogenesis of diabetes, which can be targeted for therapeutic interventions in the future.

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