Ca2+ sensitization during sustained hypoxic pulmonary vasoconstriction is endothelium dependent

Area of Science:

• Physiology
• Cardiovascular Research
• Pulmonary Circulation

Background:

• Hypoxic pulmonary vasoconstriction (HPV) is a critical physiological response regulating ventilation-perfusion matching in the lungs.
• The precise mechanisms, particularly the role of the endothelium and intracellular calcium dynamics, in sustained HPV remain incompletely understood.

Purpose of the Study:

• To investigate the impact of endothelium removal on tension and intracellular calcium ([Ca(2+)](i)) during HPV in rat intrapulmonary arteries (IPA).
• To differentiate the role of endothelin-1 from other potential endothelium-derived constrictor factors in HPV.

Main Methods:

• Rat intrapulmonary arteries (IPA) and mesenteric arteries (MA) were isolated and mounted on myographs.
• Arteries were loaded with the calcium-sensitive fluorophore fura PE-3 to measure intracellular calcium ([Ca(2+)](i)).
• Hypoxia-induced changes in tension and [Ca(2+)](i) were assessed before and after endothelial denudation, and in the presence of endothelin-1 antagonists.

Main Results:

• HPV in IPA exhibited a transient and a sustained phase; endothelial denudation abolished only the sustained phase.
• Endothelium removal did not alter [Ca(2+)](i) levels during any phase of HPV in IPA.
• Endothelin-1 antagonists did not affect HPV, though they blocked endothelin-1-induced constriction.
• Mesenteric arteries (MA) showed a transient constriction followed by vasodilation during hypoxia.

Conclusions:

• Sustained HPV in rat IPA is mediated by an endothelium-derived constrictor factor distinct from endothelin-1.
• This factor likely induces vasoconstriction through calcium sensitization rather than by increasing intracellular calcium ([Ca(2+)](i)).
• The endothelium plays a crucial role in the sustained phase of HPV, independent of direct calcium level modulation.