CASR and idiopathic pulmonary fibrosis: CaSR is also activated by various endogenous polycations (e.g., eosinophil cationic protein, major basic protein), polyamines (e.g., putrescine, spermine, and spermidine), glutathione, and basic amino acids (e.g., L-arginine and L-ornithine), which are particularly abundant in the lung [28,30] and whose expression is increased in IPF [18].