Platelet-activating factor effects on bovine pulmonary artery endothelial cells

Area of Science:

• Endothelial cell biology
• Cell signaling
• Pharmacology

Background:

• Endothelial cells (ECs) form a cobblestone monolayer in culture.
• Platelet-activating factor (PAF) is a signaling molecule known to affect various cell types.
• Phorbol-12-myristate-13-acetate (PMA) is a potent activator of protein kinase C.

Purpose of the Study:

• To investigate the effects of PAF on endothelial cell morphology and function.
• To elucidate the signaling pathways involved in PAF's action on ECs.
• To assess the impact of PAF on beta-adrenergic receptor activity in ECs.

Main Methods:

• Isolation and culture of bovine pulmonary artery ECs.
• Stimulation of ECs with PAF and PMA.
• Measurement of phosphoinositide turnover and inositol phosphate release.
• Assay of beta-adrenergic receptor-coupled adenylate cyclase activity.
• Analysis of prostacyclin and thromboxane release.

Main Results:

• PAF induced significant changes in EC shape from polygonal to spindle-like.
• PAF stimulated phosphoinositide turnover in ECs with a half-maximal activation at 10(-9) M.
• Preincubation with PAF or PMA decreased adenylate cyclase activity by 70% and 90%, respectively.
• Both PAF and PMA exposure lowered the affinity for isoproterenol threefold.

Conclusions:

• PAF triggers intracellular signaling cascades in ECs, involving Ca2+ and protein kinase C.
• PAF interaction with ECs leads to apparent beta-adrenergic receptor desensitization.
• This desensitization mechanism likely involves C kinase-mediated phosphorylation.