Activation of Store‐Operated Calcium Entry Channels Stably Increases Membrane‐Localized Calcium

Abstract

Inflammatory agonists deplete calcium from the endoplasmic reticulum and activate calcium entry in a process referred to as store‐operated calcium (SOC) entry. Calcium that permeates through SOC channels is sufficient to increase permeability although it is not clear why calcium entry, and not calcium release, is necessary to increase permeability. In our present studies, we tested the hypothesis that calcium entry is necessary to produce a sustained increase in intracellular calcium that is localized at the cell membrane. To test this hypothesis, pulmonary artery endothelial cells were loaded with either a cytosol‐localized calcium fluorophore (Fura‐2AM) or a membrane‐localized fluorophore (FFP‐18). Membrane and cytosolic calcium concentrations were calculated using the Grynkiewicz equation. Baseline membrane calcium concentrations were higher than cytosolic calcium concentrations, indicating a calcium gradient from the plasma membrane to the bulk cytosol. Upon thapsigargin‐induced SOC entry, both cytosolic and membrane calcium increased. However, cytosolic calcium decayed over time whereas membrane calcium was sustained. Collectively, these observations indicate that calcium entry through SOC channels is necessary to stably increase membrane‐associated calcium, likely necessary to induce the inter‐endothelial cell gaps that precede edema formation. Supported by HL60024.