PGE2 enhances Ca2+‐dependent ionic currents in the airway mucus gland cells

Abstract

Airway submucosal gland cell (SMGC) secretions are under the control of various secretagogues. Mechanisms of interactions between PGE2 and ACh in activating mucus cell ion current responses are examined in this study. PGE2 pretreatment sensitized ACh-induced short-circuit current (ISC) that were mediated by EP2 receptors and mimicked by forskolin. PKA inhibitors, 14–22 amide PKI (PKI) and Rp-cAMPs, prevented the effect of PGE2. Treatment with 0 [Ca2+]o or Ca2+ entry blocker, SKF96365, shifted the ACh concentration-response relationships to the right, but did not abolish PGE2-induced sensitization of the ACh response. An IP3 receptor antagonist and the Ca2+ entry blocker, 2-APB, abolished the ACh-induced response. Under whole-cell patch clamp, IP3, dialyzed in the cytosol via patch pipette upon whole-cell formation, induced immediate increases in both KCa and CaCC currents that were prolonged by simultaneous inclusion of cAMP in the internal solution. The plateau phases of both currents were related to Ca2+ entry, abolishable by treatments with 0 [Ca2+]o, Gd3+, 2-APB, or SKF96365, and were also enhanced by membrane hyperpolarization. Abundant mRNA expressions for TRPC channels (TRPC-1>>3≈6>4) were detected in the mucus cells using real-time RT-PCR. Thus, PGE2, via EP2 receptors and the cAMP/PKA pathway, enhances ACh-induced, Ca2+-mediated ionic currents in mucus cells through activating Ca2+-entry independent mechanisms that are primarily responsible for sensitization of the ACh response. ACh-induced Ca2+ entry via non-selective cation channels was also enhanced by cAMP treatment, important for sustaining the ACh-induced response [Supported by a grant from the American Heart Association to J.M.F.].