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GASTROINTESTINAL, HEPATIC, PULMONARY, AND RENAL

Prostaglandin E₂ Enhances Acetylcholine-Induced, Ca²⁺-Dependent Ionic Currents in Swine Tracheal Mucous Gland Cells

Department of Pharmacology & Toxicology, University of Mississippi Medical Center, Jackson, Mississippi

Airway submucosal gland cell (SMGC) secretions are under the control of various neurotransmitters and hormones. Interactions between different pathways, such as those mediated by cAMP and Ca²⁺, in controlling mucus or electrolyte secretions are not well understood. Prostaglandin E₂ (PGE₂) or forskolin has been shown to enhance acetylcholine (ACh)-induced short circuit current (I_SC) in SMGC mucous cell monolayers. We show that PGE₂, by activating cAMP-dependent protein kinase A (PKA), enhanced ACh-induced, Ca²⁺-mediated current and changes in [Ca²⁺]_i in mucous cells. PGE₂ pretreatment sensitized ACh-induced I_SC (I_SC) by activating endoprostanoid (EP₂) receptors. PKA inhibitors 14-22 amide PKI (PKI) and Rp-diastereomer (Rp) of cAMPs prevented the effect of PGE₂. Removing external Ca²⁺ or pretreatment with the Ca²⁺ entry blocker, SKF96365 [1-[-(3-(4-methoxyphenyl) propoxy)-4-methoxyphenethyl]-1H-imidazole hydrochloride1-[2-(4-methoxyphenyl)-2-[3-(4-methoxyphenyl) propoxy] ethyl] imidazole], shifted the concentration-response relationships for ACh to the right but did not abolish PGE₂-induced sensitization of the ACh response. An inositol 1,4,5-trisphosphate (IP₃) receptor antagonist and Ca²⁺ entry blocker, 2-aminoethoxydiphenyl borate, abolished the ACh-induced response. Charybdotoxin, but not iberiotoxin (IbTX), inhibited the ACh-induced I_SC. Clotrimazole, but not IbTX, inhibited the ACh-induced serosal K⁺ current. Under whole-cell patch clamp, ACh-induced K⁺ and Cl^– currents were coincident with increases in [Ca²⁺]_i in single mucous cells. PGE₂ or forskolin pretreatment did not induce current or [Ca²⁺]_i changes but enhanced ACh-induced currents, membrane hyperpolarization, and [Ca²⁺]_i changes. Intra-cellular dialysis with the PKA-catalytic subunit enhanced ACh-induced whole-cell current as well. These findings demonstrate that PGE₂, via EP₂ receptors and the cAMP/PKA pathway, activates Ca²⁺ entry-independent mechanisms, possibly by increasing IP₃-mediated Ca²⁺ release, resulting in the sensitization of ACh-induced currents.

Address correspondence to: Dr. Jerry M. Farley Sr., Department of Pharmacology and Toxicology, University of Mississippi Medical Center, 2500 North State Street, Jackson, MS 39216-4624. E-mail: jfarley{at}pharmacology.umsmed.edu