A volume-sensitive, IP3-insensitive Ca2+ store in vascular endothelial cells

Area of Science:

• Cell Biology
• Physiology
• Biochemistry

Background:

• The mechanisms linking physical forces, such as cell swelling, to intracellular calcium concentration ([Ca2+]i) increases are not well understood.
• Vascular endothelial cells respond to mechanical stimuli, but the precise pathways involved in calcium signaling remain elusive.

Purpose of the Study:

• To investigate the mechanism of intracellular calcium release induced by hypotonic cell swelling in vascular endothelial cells.
• To identify the source and characteristics of the calcium store involved in this volume-sensitive calcium release.

Main Methods:

• Hypotonic swelling was induced in vascular endothelial cells.
• Measurements of intracellular calcium ([Ca2+]i) were performed.
• Experiments utilized thapsigargin, La3+, Gd3+, ruthenium red, and inositol 1,4,5-trisphosphate (IP3) to probe calcium release pathways.
• Radiolabeled 45Ca2+ flux was measured in permeabilized cells.

Main Results:

• Hypotonic swelling increased [Ca2+]i independently of external calcium and membrane potential.
• Calcium release was prevented by thapsigargin and occurred from agonist-insensitive stores.
• Volume-sensitive calcium release was observed from a thapsigargin-sensitive intracellular site.
• This release was specifically due to swelling, not osmolarity or ion changes.
• The calcium store involved is distinct from mitochondria and IP3/ryanodine-sensitive stores.

Conclusions:

• A novel, stretch-activated intracellular calcium store exists in endothelial cells.
• This volume-sensitive calcium release mechanism may contribute to endothelial cell mechanosensitivity.
• The findings reveal a new pathway for physical forces to modulate intracellular calcium signaling.