Contractile effect of alpha,beta-methylene ATP on the guinea-pig isolated trachea

Purinergic signaling in the airways

Evidence for a significant role and impact of purinergic signaling in normal and diseased airways is now beyond dispute. The present review intends to provide the current state of knowledge of the involvement of purinergic pathways in the upper and lower airways and lungs, thereby differentiating the involvement of different tissues, such as the epithelial lining, immune cells, airway smooth muscle, vasculature, peripheral and central innervation, and neuroendocrine system. In addition to the vast number of well illustrated functions for purinergic signaling in the healthy respiratory tract, increasing data pointing to enhanced levels of ATP and/or adenosine in airway secretions of patients with airway damage and respiratory diseases corroborates the emerging view that purines act as clinically important mediators resulting in either proinflammatory or protective responses. Purinergic signaling has been implicated in lung injury and in the pathogenesis of a wide range of respiratory disorders and diseases, including asthma, chronic obstructive pulmonary disease, inflammation, cystic fibrosis, lung cancer, and pulmonary hypertension. These ostensibly enigmatic actions are based on widely different mechanisms, which are influenced by the cellular microenvironment, but especially the subtypes of purine receptors involved and the activity of distinct members of the ectonucleotidase family, the latter being potential protein targets for therapeutic implementation.

Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems

This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.

Effects of purinoceptor agonists on cytosolic Ca2+ concentration in swine tracheal smooth muscle cells in culture

1. The effects of various purinoceptor agonists on intracellular Ca2+ concentration ([Ca2+]i) in swine tracheal smooth muscle cells in primary culture were examined to investigate the subtype of purinoceptors in these cells. 2. ATP (1 microM to 1 mM) concentration-dependently increased [Ca2+]i which was measured by monitoring the fluorescence signal of fura2. 3. alpha, beta-Me ATP at concentrations higher than 10 microM increased [ca2+]i in the presence of extracellular Ca2+. Responses to the drug were 12 +/- 5 and 61 +/- 4% of responses to ATP (100 microM) at 100 microM and 1 mM, respectively (n = 7). The response to 100 microM ATP was inhibited by 62% in the presence of 1 mM alpha, beta-Me ATP (n = 8), though the drug at concentrations lower than that did not affect the response to ATP. 4. ATP increased [Ca2+]i in the absence of extracellular Ca2+. The response to ATP in this condition was 40% of that in the presence of extracellular Ca2+ (n = 8). 5. Neither cibacron blue 3GA (10 microM) (n = 8) nor suramin (10 and 100 microM) (n = 10) affected the response to ATP (1 microM to 100 microM). 6. The rank order of potency in the absence of extracellular Ca2+ was UTP > ATP > adenosine 5'-o-(3-thiotriphosphate) > > ADP = alpha, beta-methylene adenosine 5'-triphosphate > 2-(methylthio)-adenosine 5'-(tetrahydrogen triphosphate). 7. UTP (1 microM to 100 microM) concentration-dependently increased inositol 1,4,5-triphosphate (IP3) production. 8. These results suggest that the increase in [Ca2+]i induced by purinoceptor agonists is mediated mainly via a nucleotide receptor in swine tracheal smooth muscle cells in primary culture.

Demonstration of an ectoATP-diphosphohydrolase (E.C.3.6.1.5.) in non-vascular smooth muscles of the bovine trachea

An ectoATP-diphosphohydrolase (ATPDase) is put in evidence in non-vascular smooth muscles of the bovine trachea. The enzyme has an optimum pH of 7.0 and catalyzes the hydrolysis of the gamma- and beta-phosphate residues from extracellular triphospho- and diphosphonucleosides. It requires either Ca2+ or Mg2+ and is insensitive to ouabain, oligomycin and Ap5A. Sodium azide (20 mM), mercuric chloride (10 microM) and gossypol (35 microM) inhibit the enzyme activity by more than 45%. Polyacrylamide gel electrophoresis under non-denaturing conditions and kinetic properties, namely pH dependency profiles, heat inactivation and 60Co gamma-irradiation-inactivation curves, support the view that the same catalytic site is responsible for the hydrolysis of ATP and ADP to AMP. Accordingly, when both ATP and ADP were combined, reaction rates were not additive. With ATP, Km,app and Vmax,app were estimated at 15 +/- 2 microM and 1.9 +/- 0.1 mumol inorganic phosphate/min per mg of protein, respectively. From 60Co gamma-irradiation-inactivation curves, the molecular mass of the enzyme was estimated at 71 +/- 5 kDa. Enzyme markers indicate that the ATPDase is associated with the plasma membrane. Enzyme assays on trachea smooth muscle cells in suspension confirm that the catalytic site of this ATPDase is localized on the outer surface of the plasma membrane. Analysis of the biochemical properties shows many points of similarity between the tracheal ATPDase and the ATPDase recently described in the bovine lung.