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© The Rockefeller University Press,
0021-9525/1997//987 $5.00
The Journal of Cell Biology, Volume 138, Number 5,
, 1997 987-998
Article |
Dynamics of ATP-induced Calcium Signaling in Single Mouse Thymocytes
Extracellular ATP (ATPo) elicits a robust change in the concentration of intracellular Ca2+ ([Ca2+]i) in fura-2–loaded mouse thymocytes. Most thymocytes (60%) exposed to ATPo exhibited a biphasic rise in [Ca2+]i; [Ca2+]i rose slowly at first to a mean value of 260 nM after 163 s and then increased rapidly to a peak level of 735 nM. In many cells, a declining plateau, which lasted for more than 10 min, followed the crest in [Ca2+]i. Experiments performed in the absence of extracellular [Ca2+]o abolished the rise in thymocyte [Ca2+]i, indicating that Ca2+ influx, rather than the release of stored Ca2+, is stimulated by ATPo. ATPo- mediated Ca2+ influx was potentiated as the [Mg2+]o was reduced, confirming that ATP4– is the active agonist form. In the absence of Mg2+o, 3'-O-(4-benzoyl)benzoyl-ATP (BzATP) proved to be the most effective agonist of those tested. The rank order of potency for adenine nucleotides was BzATP4–>ATP4–>MgATP2–>ADP3–, suggesting purinoreceptors of the P2X7/P2Z class mediate the ATPo response. Phenotyping experiments illustrate that both immature (CD4–CD8–, CD4+CD8+) and mature (CD4+CD8–, CD4–CD8+) thymocyte populations respond to ATP. Further separation of the double-positive population by size revealed that the ATPo-mediated [Ca2+]i response was much more pronounced in large (actively dividing) than in small (terminally differentiated) CD4+CD8+ thymocytes. We conclude that thymocytes vary in sensitivity to ATPo depending upon the degree of maturation and suggest that ATPo may be involved in processes that control cellular differentiation within the thymus.
Abbreviations used in this paper: ATPo, extracellular ATP; BzATP, benzoyl-ATP; [Ca2+]i, intracellular calcium concentration; [Ca2+]o, extracellular calcium concentration; MHC, major histocompatibility proteins; TCR, T-cell receptor.
Please address all correspondence to Dr. Cahalan, Department of Physiology and Biophysics, University of California at Irvine, Irvine, CA 92697. Tel: (714) 824-7776; Fax: (714) 824-8540; E-mail: mcahalan{at}uci.edu
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