title: Positive allosteric modulation by ivermectin of human but not murine P2X7 receptors.
abstract: OBJECTIVE
  In mammalian cells, the anti-parasitic drug ivermectin is known as a positive allosteric modulator of the ATP-activated ion channel P2X4 and is used to discriminate between P2X4- and P2X7-mediated cellular responses. In this paper we provide evidence that the reported isoform selectivity of ivermectin is a species-specific phenomenon.
  
  
  METHODS
  Complementary electrophysiological and fluorometric methods were applied to evaluate the effect of ivermectin on recombinantly expressed and on native P2X7 receptors. A biophysical characterization of ionic currents and of the pore dilation properties is provided.
  
  
  RESULTS
  Unexpectedly, ivermectin potentiated currents in human monocyte-derived macrophages that endogenously express hP2X7 receptors. Likewise, currents and [Ca(2+) ](i)  influx through recombinant human (hP2X7) receptors were potently enhanced by ivermectin at submaximal or saturating ATP concentrations. Since intracellular ivermectin did not mimic or prevent its activity when applied to the bath solution, the binding site of ivermectin on hP2X7 receptors appears to be accessible from the extracellular side. In contrast to currents through P2X4 receptors, ivermectin did not cause a delay in hP2X7 current decay upon ATP removal. Interestingly, NMDG(+)  permeability and Yo-Pro-1 uptake were not affected by ivermectin. On rat or mouse P2X7 receptors, ivermectin was only poorly effective, suggesting a species-specific mode of action.
  
  
  CONCLUSIONS
  The data indicate a previously unrecognized species-specific modulation of human P2X7 receptors by ivermectin that should be considered when using this cell-biological tool in human cells and tissues.
authors.affiliation: Rudolf-Boehm-Institute of Pharmacology and Toxicology, Medical Faculty, University of Leipzig, Leipzig, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Nörenberg
authors.forename: H
authors.initials: H
authors.lastname: Sobottka
authors.forename: C
authors.initials: C
authors.lastname: Hempel
authors.forename: T
authors.initials: T
authors.lastname: Plötz
authors.forename: W
authors.initials: W
authors.lastname: Fischer
authors.forename: G
authors.initials: G
authors.lastname: Schmalzing
authors.forename: M
authors.initials: M
authors.lastname: Schaefer
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000494:Allosteric Regulation / Q000187:drug effects; D000818:Animals; D000977:Antiparasitic Agents / Q000494:pharmacology*; D001253:Astrocytes / Q000187:drug effects / Q000502:physiology; D001583:Benzoxazoles / Q000378:metabolism; D002118:Calcium / Q000502:physiology; D002478:Cells, Cultured; D005456:Fluorescent Dyes / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D007559:Ivermectin / Q000494:pharmacology*; D008264:Macrophages / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D009000:Monocytes / Q000166:cytology; D011806:Quinolinium Compounds / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D058848:Receptors, Purinergic P2X4 / Q000502:physiology; D058486:Receptors, Purinergic P2X7 / Q000502:physiology*; D013045:Species Specificity
chemical_list: D000977:Antiparasitic Agents; D001583:Benzoxazoles; D005456:Fluorescent Dyes; D011806:Quinolinium Compounds; D058848:Receptors, Purinergic P2X4; D058486:Receptors, Purinergic P2X7; C089813:YO-PRO 1; D007559:Ivermectin; D000255:Adenosine Triphosphate; D002118:Calcium