Functional characterisation of phosphodiesterase isoforms in murine airway smooth muscle

Sujeen Chandramoorthy, James Moffatt. Division of Biomedical Sciences, St George's, University of London, SW17 0RE London, United Kingdom.

Phosphodiesterase (PDE) inhibitors are potential drugs for the treatment of respiratory diseases such as asthma and chronic obstructive pulmonary disease. Although mice are frequently used in respiratory drug discovery programmes, the PDE isoform(s) present in airway smooth muscle does not appear to have been previously characterised. This study examined the effects of several isoform-selective PDE inhibitors on the contractility of the isolated mouse trachea.

Tracheal segments (2 per animal; BALB/c 6-8 weeks old) were suspended on stainless steel hooks in conventional tissue baths for isometric recording of airway smooth muscle contractility. Each preparation was exposed to 100 uM methacholine to determine maximal force production (FMAX). After washing, preparations were contracted to 40-50% of FMAX with methacholine and PDE inhibitors were added in cumulative concentrations. pEC50 (-log molar concentration causing 50% response) values for each inhibitor were estimated by non-linear regression of the concentration-effect curves using GraphPad Prism (Table 1).

Table 1

Milrinone, MY-5445 and zaprinast caused relaxations only at concentrations greater than 10 μM, and were not different to vehicle (DMSO) controls. The effects of the PDE4 selective inhibitors RO 20-1724 and rolipram suggest that this isoform predominates in this preparation. The apparent lack of effect of milrinone suggests that, unlike human airway smooth muscle, PDE3 does not make a significant contribution to the regulation of murine airway smooth muscle tone.