Extracellular ATP‐dependent activation of plasma membrane Ca 2+ pump in HEK‐293 cells

It is well known that extracellular ATP (ATP o ) elevates the intracellular Ca 2+ concentration ([Ca 2+ ] i ) by inducing Ca 2+ influx or mobilizing Ca 2+ from internal stores via activation of purinoceptors in the plasma membrane. This study shows that ATP o also activates the plasma membrane Ca 2+ pumps (PMCPs) to bring the elevated [Ca 2+ ] i back to the resting level in human embryonic kidney‐293 (HEK‐293) cells. The duration of ATP o ‐induced intracellular Ca 2+ transients was significantly increased by PMCP blockers, La 3+ or orthovanadate. In contrast, replacement of extracellular Na + with NMDG + , a membrane‐impermeable cation, had no significant effect on duration, thus suggesting that Na + /Ca 2+ exchangers do not participate in the ATP o ‐induced Ca 2+ transient. A rapid and significant decrease in [Ca 2+ ] i , which was not dependent on extracellular Na + , was induced by ATP o in cells pretreated with thapsigargin (TG). This decrease was blocked by orthovanadate, indicating that it was caused by PMCPs rather than sarco/endoplasmic reticulum Ca 2+ pumps (SERCPs). UTP and ATPγS also caused a decrease in [Ca 2+ ] i in cells pretreated with TG, although they were less effective than ATP. The effect of UTP implies the involvement of both P2Y 1 and P2Y 2 receptors, while the effect of ATPγS implies no significant role of ectophosphorylation and agonist hydrolysis in the agonist‐induced [Ca 2+ ] i decreases. These results point to a role of PMCPs in shaping the Ca 2+ signal and in restoring the resting [Ca 2+ ] i level to maintain intracellular Ca 2+ homeostasis after agonist stimulation.British Journal of Pharmacology (2000) 131 , 370–374; doi: 10.1038/sj.bjp.0703563