Cellular mechanisms controlling EDRF/NO formation in endothelial cells.

Area of Science:

• Endothelial cell biology
• Molecular mechanisms of nitric oxide synthesis
• Calcium signaling

Background:

• Endothelial nitric oxide (NO) synthesis is crucial for vascular function.
• The precise molecular mechanisms linking intracellular calcium (Ca2+) to NO production require further elucidation.
• Calmodulin's role in mediating Ca2+-dependent NO synthesis in endothelial cells is a key area of investigation.

Purpose of the Study:

• To investigate how Ca2+ enters endothelial cells and regulates NO synthesis.
• To determine the role of Ca2+-calmodulin complex in activating endothelial NO synthase (eNOS).
• To explore the influence of endothelial cell membrane potential on Ca2+ influx and subsequent NO production.

Main Methods:

• Quantification of L-arginine-dependent NO synthesis via soluble guanylate cyclase activation.
• Assessment of Ca2+-dependent activation and inhibition by calmodulin antagonists (mastoparan, melittin, calcineurin).
• Experimental manipulation of intracellular Ca2+ levels using K+-induced depolarization and K+ channel activators (Hoe 234).

Main Results:

• Free Ca2+ concentration-dependently enhanced NO synthesis with an EC50 of 0.3 microM.
• Ca2+-dependent activation was inhibited by calmodulin antagonists in a reversible manner.
• Removal and re-addition of calmodulin demonstrated its essential role in Ca2+-dependency of eNOS.
• Endothelial cell depolarization inhibited sustained Ca2+ response to bradykinin, while hyperpolarization augmented it.
• Changes in Ca2+ signaling correlated with agonist-induced endothelial-derived relaxing factor/NO release.

Conclusions:

• Ca2+-calmodulin directly activates endothelial NO synthase, linking agonist-induced Ca2+ increases to NO formation.
• Endothelial cell membrane potential significantly influences agonist-induced Ca2+ influx.
• Modulation of membrane potential impacts Ca2+ influx and consequently regulates endothelial NO synthesis.