Introduction & Aims: The calcium sensing receptor (CaSR) detects changes in extracellular calcium (Ca2+o) to maintain Ca2+o homeostasis. The CaSR is upregulated in asthma, and allosteric CaSR agonists, such as polyamines, induce bronchoconstriction. Negative allosteric modulators (NAMs; e.g. NPS2143) reduce airway inflammation, remodelling and hyperresponsiveness in a mouse chronic asthma model (Yarova et al, 2015) but whether NAMs oppose acute bronchoconstriction is unknown. This study aims to investigate the contribution of the CaSR to airway reactivity, by comparing contraction to polyamines (CaSR agonists) and methacholine (MCh), and the potential dilator effects of NAMs and salbutamol, currently used in the treatment of asthma.
Methods: Calcium mobilisation assays in CaSR-HEK293 cells were used for quantifying the potency, affinity and efficacy of polyamines (spermine, spermidine, agmatine and putrescine) at the wild type CaSR. Precision cut lung slices prepared from C57Bl/6 mice were used to assess contraction to polyamines and MCh, and relaxation to salbutamol and NAMs.
Results: In calcium mobilisation assays, spermine has the highest potency, affinity and efficacy (pEC50: 4.51±0.02; pKB: 3.64±0.04;