Prostaglandin E2-EP3 Receptor Signalling Causes Depolarisation of the Isolated Vagus Nerve Via TRPV1 and TRPA1

Sarah Maher, Megan Grace, Mark Birrell, Maria Belvisi. Imperial College, London, United Kingdom.

Prostaglandin E2 (PGE2) confers both bronchodilator and anti-inflammatory activity in asthmatic subjects, however, inhaled PGE2 can cause irritancy of the upper airway resulting in a reflex cough. The cough reflex is under the control of sensory afferent nerve fibres that innervate the lungs via the vagus nerve. Having previously shown that PGE2 causes sensory nerve irritation and cough via the EP3 receptor, we wanted to determine how activation of this receptor leads to nerve depolarisation. The Transient Receptor Potential Vanilloid 1 (TRPV1) and Ankyrin 1 (TRPA1) are known to be expressed on sensory nerves. Specific agonists of these channels depolarise the nerve therefore we investigated the role of these ion channels in PGE2-induced depolarisation.

The effect of TRPV1 and TRPA1 antagonists on the depolarisation induced by PGE2 (10μM) was investigated in mouse (male C57bl/6j or receptor deficient mice, 18-20g) and guinea-pig (male Dunkin Hartley, 300-350g) isolated vagal nerve preparations. In guinea-pig, capsazepine (TRPV1, 10μM) and AP-18 (TRPA1, 10μM) significantly inhibited PGE2-induced depolarisation of the vagus nerve by 45.0 ± 3.1% and 48.5 ± 3.6% respectively (n=6, p<0.05, paired t-test), and in combination, by 88.2 ± 5.4% (n=6, p<0.05 paired t-test). The data in mice parallels that in guinea-pig; capsazepine (10μM) and AP-18 (30μM) inhibited PGE2-induced depolarisation by 49.2 ± 4.8% and 50.5 ± 3.1% respectively and in combination by 90.2 ± 5.5 % (n=4, p<0.05 paired t-test). Using Trpv1-/- and Trpa1-/- mice we illustrate that the response to PGE2 compared to wild type is significantly decreased (n=6, P<0.05, Kruskal-Wallis with Dunns post hoc test). Furthermore, we confirm that 10μM capsazepine in isolated nerves from Trpa1-/- mice and 30μM AP-18 in isolated nerves from Trpv1-/- mice significantly inhibit PGE2 (10μM) by 92.9 ± 5.8% and 94.5 ± 4.5% respectively (n=4, p<0.05 paired t-test).

In conclusion, we have described data that furthers our understanding of the mechanism of PGE2-induced sensory nerve activation and cough and have shown that depolarisation in response to PGE2 in isolated sensory nerves is mediated by both TRPV1 and TRPA1 channels.

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