Dynamics of ATP-Induced Calcium Signaling in Single Mouse Thymocytes

• Published in: The Journal of cell biology 1997-09, Vol.138 (5), p.987-998
• Main Authors: Ross, Paul E., Ehring, George R., Cahalan, Michael D.
• Format: Article
• Language: English
• Subjects: Acinar cells; Adenosine Triphosphate - analogs & derivatives; Adenosine Triphosphate - pharmacology; Agonists; Animals; Apoptosis; Calcium; Calcium - metabolism; CD4 Antigens - analysis; CD8 Antigens - analysis; Cells; Cells, Cultured; Cellular biology; Female; Immunophenotyping; Kinetics; Magnesium - metabolism; Mast cells; Mice; Mice, Inbred BALB C; Nucleotides; Purinergic receptors; Receptors; Rodents; Signal Transduction; T lymphocytes; T-Lymphocytes - cytology; T-Lymphocytes - drug effects; T-Lymphocytes - physiology; Thymocytes
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.138.5.987

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 $\text{BzATP}^{4-}>\text{ATP}^{4-}>\text{MgATP}^{2-}>\text{ADP}^{3-}$, 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.