Effect of erythromycin on ATP-induced intracellular calcium response in A549 cells

ATP induced a biphasic increase in the intracellular Ca²⁺ concentration ([Ca²⁺](i)), an initial spike, and a subsequent plateau in A549 cells. Erythromycin (EM) suppressed the ATP-induced [Ca²⁺](i) spike but only in the presence of extracellular calcium (Ca(o)/²⁺). It was ineffective against ATP- and UTP-induced inositol 1,4,5-trisphosphate [Ins(1,4,5)P₃] formation and UTP-induced [Ca²⁺](i) spike, implying that EM perturbs Ca²⁺ influx from the extracellular space rather than Ca²⁺release from intracellular Ca²⁺ stores via the G protein-phospholipase C- Ins(1,4,5)P₃ pathway. Averapamil-sensitive, KCl-induced increase in [Ca²⁺](i) and the Ca²⁺ influx activated by Ca²⁺ store depletion were insensitive to EM. 3'-O-(4-benzoylbenzoyl)-ATP evoked an Ca(o)/²⁺-dependent [Ca²⁺](i) response even in the presence of verapamil or the absence of extracellular Na⁺, and this response was almost completely abolished by EM pretreatment. RT-PCR analyses revealed that P2X₄ as well as P2Y₂, P2Y₄, and P2Y₆ are coexpressed in this cell line. These results suggest that in A549 cells 1) the coexpressed P2X₄ and P2Y₂/P2Y₄ subtypes contribute to the ATP-induced [Ca²⁺](i) spike and 2) EM selectively inhibits Ca²⁺ influx through the P2X channel. This action of EM may underlie its clinical efficacy in the treatment of airway inflammation.