Interplay between the NO pathway and elevated [Ca2+]i enhances ciliary activity in rabbit trachea.

Area of Science:

• Cell Biology
• Respiratory Physiology

Background:

• Purinergic stimulation by extracellular nucleotides like ATP is known to affect airway function.
• The precise molecular mechanisms linking purinergic signaling to ciliary activity remain incompletely understood.

Purpose of the Study:

• To investigate the role of intracellular calcium concentration ([Ca2+]i) and protein kinases in purinergic stimulation of ciliary beat frequency (CBF) in rabbit airway ciliated cells.

Main Methods:

• Simultaneous measurement of [Ca2+]i and CBF in rabbit airway ciliated cells.
• Pharmacological manipulation using inhibitors (U-73122, suramin, GF 109203X, chelerythrine chloride, Rp-cAMPS) and activators (phorbol 12-myristate 13-acetate, forskolin, dibutyryl-cAMP, dibutyryl-cGMP) of various signaling pathways.
• Stimulation with extracellular ATP, UTP, and ionomycin.

Main Results:

• Extracellular ATP and UTP induced rapid increases in both [Ca2+]i and CBF, dependent on phospholipase C and P2 receptors.
• Inhibition of protein kinase C (PKC) or protein kinase A (PKA) did not affect ATP-induced responses.
• Activation of protein kinase G (PKG) by dibutyryl-cGMP significantly elevated CBF when [Ca2+]i was raised, suggesting a role in calcium-dependent ciliary activation.

Conclusions:

• Extracellular ATP-induced calcium influx activates the nitric oxide (NO) pathway, leading to PKG activation.
• PKG plays a critical role in enhancing CBF and maintaining elevated [Ca2+]i through a positive feedback mechanism.
• PKG is a key mediator in purinergic stimulation of airway ciliary activity.