Received for publication May 18, 2005.
Revised August 9, 2005.
Accepted for publication August 10, 2005.

THE EFFECTS OF EXTRACELLULAR PURINES AND PYRIMIDINES ON HUMAN AIRWAY SMOOTH MUSCLE CELLS

Abstract

Extracellular ATP and UTP modulate the function of many cell types through the stimulation of specific P2 receptors and the inhalation of UTP has been proposed as a therapeutic means of increasing mucociliary clearance in cystic fibrosis patients. The aim of this study was to determine whether P2 receptors are present and functional in human airway smooth muscle (HASM) cells. Experiments were conducted on primary cultures of HASM cells. RT-PCR and Western blot analysis showed that P2Y₁, P2Y₂, P2Y₄ and P2Y₆ receptor subtypes are expressed. Exposure to extracellular ATP, UTP, ADP and UDP at concentrations ranging from 10^-6 to 10^-4 M, produced significant increases in intracellular Ca²⁺ which peaked to 491±51 nM (p<0.001) with ATP 10^-5M.and to 321±30 nM with UTP 10^-4M. ATP and UTP also induced HASM cell contraction, decreasing cell length by 9.9±4.3% and 5.6±2.0% respectively. Pretreatment of the cells with UTP for short periods of time (10 and 30 minutes) enhanced the peak Ca⁺² release to UTP while repeated and prolonged pretreatment with UTP decreased it. These results indicate that several subtypes of P2Y receptors are present and functional in HASM cells. They also show that the response of the receptors is increased following short periods of exposure to UTP and decreased following prolonged and repeated exposure. Considering that ATP and UTP are endogenous mediators and that analogs of UTP could be used as a therapeutic modality, the role of extracellular triphosphate nucleotides in physiological and pathphysiological processes in the airways warrants further investigation.

Key words: ATP, P2 receptors, UTP, calcium release, contraction, signaling

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