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

ATP induced a biphasic increase in the intracellular Ca2+ concentration([Ca 2+](i)), an initial spike, and a subsequent plateau in A549 cells. Erythrom ycin (EM) suppressed the ATP-induced [Ca2+](i) spike but only in the presen ce of extracellular calcium (Ca-o(2+)). It was ineffective against ATP- and UTP-induced inositol 1,4,5-trisphosphate [Ins(1,4,5)P-3] formation and UTP -induced [Ca2+](i) spike, implying that EM perturbs Ca2+ influx from the ex tracellular space rather than Ca2+ release from intracellular Ca2+ stores v ia the G protein-phospholipase C-Ins(1,4,5)P-3 pathway. A verapamil-sensiti ve, 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 complete ly abolished by EM pretreatment. RT-PCR analyses revealed that P2X(4) as we ll as P2Y(2), P2Y(4), and P2Y(6) are coexpressed in this cell line. These r esults suggest that in A549 cells 1) the coexpressed P2X(4) and P2Y(2)/P2Y( 4) subtypes contribute to the ATP-induced [Ca2+](i) spike and 2) EM selecti vely inhibits Ca2+ influx through the P2X channel. This action of EM may un derlie its clinical efficacy in the treatment of airway inflammation.