Extracellular ATP is a potent surfactant secretagogue but its origin in the alveolus, its mechanism(s) of release and its regulatory pathways remain unknown. Previously, we showed that hypotonic swelling of alveolar A549 cells induces Ca²⁺‐dependent secretion of several adenosine and uridine nucleotides, implicating regulated exocytosis. In this study, we examined sources of Ca²⁺ for the elevation of intracellular Ca²⁺ concentration ([Ca²⁺]_i) evoked by acute 50% hypotonic stress and the role of autocrine purinergic signalling in Ca²⁺‐dependent ATP release. We found that ATP release does not directly involve Ca²⁺ influx from extracellular spaces, but depends entirely on Ca²⁺ mobilization from intracellular stores. The [Ca²⁺]_i response consisted of slowly rising elevation, representing mobilization from thapsigargin (TG)‐insensitive stores and a superimposed rapid spike due to Ca²⁺ release from TG‐sensitive endoplasmic reticulum (ER) Ca²⁺ stores. The latter could be abolished by hydrolysis of extracellular triphospho‐ and diphosphonucleotides with apyrase; blocking P2Y₂/P2Y₆ receptors of A549 cells with suramin; blocking UDP receptors (P2Y₆) with pyridoxal phosphate 6‐azophenyl‐2′,4′‐disulfonic acid (PPADS); emptying TG‐sensitive stores downstream with TG or caffeine in Ca²⁺‐free extracellular solution; or blocking the Ca²⁺‐release inositol 1,4,5‐triphosphate receptor channel of the ER with 2‐aminoethyldiphenylborinate. These data demonstrate that the rapid [Ca²⁺]_i spike results from the autocrine stimulation of IP₃/Ca²⁺‐coupled P2Y, predominantly P2Y₆, receptors, accounting for ∼70% of total Ca²⁺‐dependent ATP release evoked by hypotonic shock. Our study reveals a novel paradigm in which stress‐induced ATP release from alveolar cells is amplified by the synergistic autocrine/paracrine action of coreleased uridine and adenosine nucleotides. We suggest that a similar mechanism of purinergic signal propagation operates in other cell types.