Extracellular ATP causes lysis of mouse thymocytes and activates a plasma membrane ion channel.
Extracellular ATP (ATPo) caused a concentration-dependent lysis of mouse thymocytes. Lysis, as judged by release of the cytosolic enzyme lactate dehydrogenase, was preceded by depolarization of the plasma membrane and by Ca2+ influx. Both Na+ uptake (which sustained plasma membrane depolarization) and Ca2+ influx showed (1) the same dependence on the ATPo concentration; (2) the same nucleotide specificity; and (3) the same Hill coefficient. However, whereas the rise in the cytosolic free Ca2+ concentration ([Ca2+]i) was fully inhibited by the known Ca2+ blocker verapamil, plasma membrane depolarization was enhanced under these conditions. Plasma membrane depolarization was greater and was shifted to lower ATPo concentrations in the absence of extracellular Ca2+ (Ca2+o), whereas the rise in [Ca2+]i was greater in Na(+)-free media. Plasma membrane depolarization also occurred in Na(+)-free choline- or methylglucamine-containing media, and was potentiated by chelation of free divalent ions with EDTA, supporting previous reports pointing to ATP4-as the active species. Among a number of purine and pyrimidine nucleotides, only adenosine 5'-[gamma-thio]triphosphate and ADP were partially effective. Furthermore, ethidium bromide (Mr 380), Lucifer Yellow (Mr 463) and Eosin Yellowish (Mr 692) did not permeate through the ATPo-activated channel. These findings suggest that lytic effects of ATPo in mouse thymocytes depend on the activation of a membrane channel with low selectivity for cations and an Mr cut-off of 200.
Pizzo
P
P
National Research Council Unit for the Study of the Physiology of Mitochondria, University of Padova, Italy.
Zanovello
P
P
Bronte
V
V
Di Virgilio
F
F
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008807:Mice, Inbred BALB C; D012265:Ribonucleotides / Q000494:pharmacology; D013601:T-Lymphocytes / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D014700:Verapamil / Q000494:pharmacology
D007473:Ion Channels; D012265:Ribonucleotides; D000255:Adenosine Triphosphate; D014700:Verapamil; D002118:Calcium