Ca(2+)-activated Cl- currents in pulmonary arterial myocytes

Area of Science:

• Cardiovascular Physiology
• Smooth Muscle Electrophysiology
• Ion Channel Function

Background:

• Pulmonary arterial smooth muscle cells (PASMCs) play a critical role in regulating pulmonary blood flow.
• Chloride currents (Cl-) are implicated in PASMC function, but their specific roles and regulation remain incompletely understood.
• Understanding ion channel activity in PASMCs is vital for addressing pulmonary vascular diseases.

Purpose of the Study:

• To electrophysiologically characterize calcium-activated chloride currents (ICl(Ca)) in rat pulmonary arterial smooth muscle cells.
• To investigate the distribution and activation properties of ICl(Ca) across different segments of the pulmonary arterial tree.
• To elucidate the role of intracellular calcium and ATP in the regulation of ICl(Ca).

Main Methods:

• Whole-cell patch-clamp technique applied to isolated rat PASMCs from main pulmonary artery and small vessels.
• Flash photolysis of caged calcium (Nitr-5) to rapidly increase cytosolic free calcium.
• Ion substitution and pharmacological agents used to identify ion species and signaling pathways.
• Caffeine application to assess calcium release-dependent activation.

Main Results:

• A calcium-activated chloride current, ICl(Ca), was identified in rat PASMCs.
• ICl(Ca) was present in 80% of cells from the main pulmonary artery but only 43% from small vessels (200-400 μm ID).
• ICl(Ca) activation was independent of photolytic by-products and functional without pipette ATP; caffeine also activated ICl(Ca).

Conclusions:

• This study provides the first electrophysiological evidence of ICl(Ca) in small pulmonary arterial vessels.
• The differential distribution and activation of ICl(Ca) suggest distinct calcium handling or channel regulation throughout the pulmonary circulation.
• Findings highlight potential differences in PASMC electrophysiology across the pulmonary vasculature, impacting vascular tone regulation.