Dependence of endothelin-1 secretion on Ca2+

Area of Science:

• Endothelial cell biology
• Molecular signaling
• Cardiovascular research

Background:

• Endothelin-1 (ET-1) is a potent vasoconstrictor peptide implicated in cardiovascular diseases.
• The intracellular mechanisms regulating ET-1 release, particularly the roles of calcium (Ca2+) and protein kinase C (PKC), are not fully elucidated.

Purpose of the Study:

• To investigate the influence of intracellular free Ca2+ concentration ([Ca2+]i) and PKC activity on ET-1 secretion from cultured porcine aortic endothelial cells.

Main Methods:

• Cultured porcine aortic endothelial cells were treated with various agents to modulate [Ca2+]i (e.g., Ca2+ entry blockers, chelators, ionophores) and PKC activity (inhibitors, activators).
• ET-1 accumulation within cells and secretion into the conditioned medium were quantified over time.
• Cyclic guanosine-3',5'-monophosphate (cGMP) levels were also measured.

Main Results:

• Both reduction and elevation of [Ca2+]i significantly decreased ET-1 secretion and intracellular levels, demonstrating a bell-shaped concentration-response curve.
• PKC inhibitors markedly reduced basal ET-1 secretion, while a PKC activator (phorbol 12-myristate 13-acetate) increased secretion, an effect abolished by EGTA.
• Basal ET-1 secretion showed a poor correlation with cGMP levels.

Conclusions:

• ET-1 release exhibits a bell-shaped relationship with [Ca2+]i, with maximal release at resting concentrations and reduced release at both lower and higher levels.
• Ca2+-dependent PKC activity is a critical determinant of basal ET-1 release from endothelial cells.