Escherichia coli is the dominant facultative bacterium in the normal intestinal flora. E.coli is, however, also responsible for the majority of serious extraintestinal infections. There are distinct serotypical differences between facultative and invasive E.coli-strains. Invasive strains frequently produce virulence factors as a-haemolysin (HlyA), which is described to induce haemolysis by forming pores in the erythrocyte membrane, with subsequent swelling and lysis. We have recently discovered that this pore-former triggers ATP release and P2 receptor activation to mediate the full haemolytic action. Non-selective ATP-receptor (P2) antagonists (PPADS, suramin) and ATP scavengers (apyrase, hexokinase) concentration dependently inhibited HlyA-induced lysis of equine, murine and human erythrocytes. The pattern of responsiveness to more selective P2-antagonists implicates that both P2X ₁ and P2X₇ receptors are involved in HlyA-induced haemolysis in all three species. In addition, our results also propose a role for the pore-protein, pannexin 1, in HlyA- induced haemolysis, as non-selective inhibitors of this channel significantly reduced haemolysis in the three species. Our results also pinpoints that HlyA-induced lysis is preceded by a severe shrinkage and crenation of the erythrocytes. The volume reduction is the result of Ca²⁺-mediated activation of K_Ca3.1 (or Gardos channel) and TMEM16A, and inhibition or lack of these channels increased HlyA-induced haemolysis considerably. In conclusion, activation of P2X receptors and possibly also pannexins augment haemolysis induced by the bacterial toxin, HlyA. These findings potentially have clinical perspectives as P2-antagonists may ameliorate symptoms during sepsis with haemolytic bacteria.