Flow-induced calcium transients in single endothelial cells: spatial and temporal analysis

Area of Science:

• Cellular biology
• Physiology
• Biophysics

Background:

• Endothelial cells (EC) are crucial for responding to hemodynamic forces.
• Flow-mediated release of endothelial-derived relaxing factors is linked to intracellular calcium ([Ca2+]i) increases in EC.

Purpose of the Study:

• To investigate the effects of fluid shear stress on endothelial cell intracellular calcium ([Ca2+]i).
• To understand the dynamic changes and spatial distribution of [Ca2+]i in response to flow.

Main Methods:

• Endothelial cells were subjected to controlled fluid shear stress using parallel-plate flow chambers and glass capillary tubes.
• Single-cell intracellular calcium ([Ca2+]i) was measured using the fura-2 fluorescent indicator.
• Comparisons were made with rat aortic smooth muscle cells.

Main Results:

• Initiation of flow (30 dyn/cm2 shear stress) caused a rapid increase in [Ca2+]i within 30 seconds, peaking at ~4x basal levels.
• [Ca2+]i then stabilized at a plateau (~2x basal) for over 5 minutes, with higher concentrations observed in nuclear and peri-membrane regions compared to the cytosol.
• The [Ca2+]i response was repeatable upon re-initiation of flow and was not abolished by removing extracellular calcium, indicating intracellular calcium stores are involved.

Conclusions:

• Endothelial cells exhibit a complex, nonhomogeneous intracellular calcium response to fluid shear stress.
• This response is mediated by multiple mechanisms, potentially involving both intracellular calcium release and influx.
• The dynamic [Ca2+]i changes in EC likely play a role in both immediate and long-term adaptations to hemodynamic forces.