Calcium sensing receptor in developing human airway smooth muscle

Airway smooth muscle (ASM) regulation of airway structure and contractility is critical in fetal/neonatal physiology in health and disease. Fetal lungs experience higher Ca²⁺ environment that may impact extracellular Ca²⁺ (Ca²⁺]_o) sensing receptor (CaSR). Well-known in the parathyroid gland, CaSR is also expressed in late embryonic lung mesenchyme. Using cells from 18-22 week human fetal lungs, we tested the hypothesis that CaSR regulates intracellular Ca²⁺ (Ca²⁺]_i) in fetal ASM (fASM). Compared with adult ASM, CaSR expression was higher in fASM, while fluorescence Ca²⁺ imaging showed that Ca²⁺]_i was more sensitive to altered Ca²⁺]_o. The fASM Ca²⁺]_i responses to histamine were also more sensitive to Ca²⁺]_o (0–2 mM) compared with an adult, enhanced by calcimimetic R568 but blunted by calcilytic NPS2143. Ca²⁺]_i was enhanced by endogenous CaSR agonist spermine (again higher sensitivity compared with adult). Inhibition of phospholipase C (U73122; siRNA) or inositol 1,4,5-triphosphate receptor (Xestospongin C) blunted Ca²⁺]_o sensitivity and R568 effects. NPS2143 potentiated U73122 effects. Store-operated Ca²⁺ entry was potentiated by R568. Traction force microscopy showed responsiveness of fASM cellular contractility to Ca²⁺]_o and NPS2143. Separately, fASM proliferation showed sensitivity to Ca²⁺]_o and NPS2143. These results demonstrate functional CaSR in developing ASM that modulates airway contractility and proliferation.