Prostanoid receptors of the EP3 subtype mediate inhibition of evoked [3H]acetylcholine release from isolated human bronchi

Abstract

1. The release of neuronal [3H]acetylcholine (ACh) from isolated human bronchi after labelling with [3H]choline was measured to investigate the effects of prostanoids. 2. A first period of electrical field stimulation (S1) caused a [3H]ACh release of 320+/-70 and 200+/-40 Becquerel (Bq) g(-1) in epithelium-denuded and epithelium-containing bronchi respectively (P>0.05). Subsequent periods of electrical stimulation (Sn, n=2, 3, and 4) released less [3H]ACh, i.e. decreasing Sn/ S1 values were obtained (0.76+/-0.09, 0.68+/-0.07 and 0.40+/-0.04, respectively). 3. Cumulative concentrations (1-1000 nM) of EP-receptor agonists like prostaglandin E2, nocloprost, and sulprostone (EP1 and EP3 selective) inhibited evoked [3H]ACh release in a concentration dependent manner with IC50 values between 4- 14 nM and maximal inhibition of about 70%. 4. The inhibition of evoked [3H]ACh release by prostaglandin E2, nocloprost and sulprostone was not affected by the DP-, EP1- and EP2-receptor antagonist AH6809 at a concentration of 3 microM, i.e. a 3-30 times greater concentration than its affinity (pA2 values) at the respective receptors. 5. Circaprost (IP-receptor agonist; 1-100 nM), iloprost (IP- and EP1-receptor agonist; 10-1000 nM) and U-46619 (TP-receptor agonist; 100-1000 nM) did not significantly affect [3H]ACh release. 6. Blockade of cyclooxygenase by 3 microM indomethacin did not significantly modulate evoked [3H]ACh release in epithelium-containing and epithelium-denuded bronchi. Likewise, the combined cyclo- and lipoxygenase inhibitor BW-755C (20 microM) did not affect evoked [3H]ACh release. 7. In conclusion, applied prostanoids appear to inhibit [3H]ACh release in epithelium-denuded human bronchi under the present in vitro conditions, most likely via prejunctional prostanoid receptors of the EP3 subtype.