Faculty Collaboration Database

Imidazobenzodiazepine PI320 Relaxes Mouse Peripheral Airways by Inhibiting Calcium Mobilization. Am J Respir Cell Mol Biol 2022 Oct;67(4):482-490

Date

07/02/2022

Pubmed ID

35776523

Pubmed Central ID

PMC9564932

DOI

10.1165/rcmb.2022-0084OC

Scopus ID

2-s2.0-85139536374 (requires institutional sign-in at Scopus site)   1 Citation

Abstract

Asthma is a common respiratory disease characterized, in part, by excessive airway smooth muscle (ASM) contraction (airway hyperresponsiveness). Various GABA_AR (γ-aminobutyric acid type A receptor) activators, including benzodiazepines, relax ASM. The GABA_AR is a ligand-operated Cl^- channel best known for its role in inhibitory neurotransmission in the central nervous system. Although ASM cells express GABA_ARs, affording a seemingly logical site of action, the mechanism(s) by which GABA_AR ligands relax ASM remains unclear. PI320, a novel imidazobenzodiazepine designed for tissue selectivity, is a promising asthma drug candidate. Here, we show that PI320 alleviates methacholine (MCh)-induced bronchoconstriction in vivo and relaxes peripheral airways preconstricted with MCh ex vivo using the forced oscillation technique and precision-cut lung slice experiments, respectively. Surprisingly, the peripheral airway relaxation demonstrated in precision-cut lung slices does not appear to be GABA_AR-dependent, as it is not inhibited by the GABA_AR antagonist picrotoxin or the benzodiazepine antagonist flumazenil. Furthermore, we demonstrate here that PI320 inhibits MCh-induced airway constriction in the absence of external Ca², suggesting that PI320-mediated relaxation is not mediated by inhibition of Ca²⁺ influx in ASM. However, PI320 does inhibit MCh-induced intracellular Ca²⁺ oscillations in peripheral ASM, a key mediator of contraction that is dependent on sarcoplasmic reticulum Ca²⁺ mobilization. Furthermore, PI320 inhibits peripheral airway constriction induced by experimentally increasing the intracellular concentration of inositol triphosphate (IP₃). These novel data suggest that PI320 relaxes murine peripheral airways by inhibiting intracellular Ca²⁺ mobilization in ASM, likely by inhibiting Ca²⁺ release through IP₃Rs (IP₃ receptors).

Author List

Perez-Zoghbi JF, Sajorda DR, Webb DA, Arnold LA, Emala CW, Yocum GT

Author

Alexander (Leggy) Arnold PhD Professor in the Chemistry & Biochemistry department at University of Wisconsin - Milwaukee

MESH terms used to index this publication - Major topics in bold

Animals
Asthma
Calcium
Calcium Signaling
Flumazenil
Inositol
Ligands
Lung
Methacholine Chloride
Mice
Muscle Contraction
Muscle, Smooth
Picrotoxin
gamma-Aminobutyric Acid