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Volume 271, Number 39, Issue of September 27, 1996 pp. 23946-23953
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.

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Regulation of cADP-ribose-induced Ca²⁺ Release by Mg²⁺ and Inorganic Phosphate

(Received for publication, April 15, 1996, and in revised form, July 8, 1996)

Andreas H. Guse , Cristina P. da Silva , Karin Weber , Gloria A. Ashamu , Barry V. L. Potter and Georg W. Mayr

From the  University of Hamburg, Institute of Physiological Chemistry, Department of Enzyme Chemistry, Grindelallee 117, D-20146 Hamburg, Germany and  University of Bath, School of Pharmacy and Pharmacology, Claverton Down, Bath BA2 7AY, United Kingdom

cADP-ribose (cADPr) has recently been shown to release Ca²⁺ from an intracellular store of permeabilized T lymphocyte cell lines (Guse, A. H., da Silva, C. P., Emmrich, F., Ashamu, G. A., Potter, B. V. L., and Mayr, G. W. (1995) J. Immunol. 155, 3353-3359). Using permeabilized Jurkat and HPB.ALL T lymphocytes, the effects of varying concentrations of inorganic phosphate and Mg²⁺ on cADPr-induced Ca²⁺ release were investigated. cADPr-induced Ca²⁺ release was dependent on the concentration of inorganic phosphate, showing very low Ca²⁺ release activity between 0.5 and 2 mM inorganic phosphate. At 4 to 5 mM inorganic phosphate, the cADPr-induced Ca²⁺ release was much more pronounced, reaching maximal values at 10 mM inorganic phosphate. The underlying mechanism for this stimulatory effect was an increased loading of the cADPr-sensitive Ca²⁺ store, which was demonstrated by enhanced resequestration of Ca²⁺ selectively into the cADPr-sensitive Ca²⁺ store. The free Mg²⁺ concentration also influenced cADPr-induced Ca²⁺ release in permeabilized cells: at 0 and 8.58 mM the release was nearly completely abolished, whereas at 1.06 mM maximal Ca²⁺ release by cADPr was observed. High performance liquid chromatographic analysis of exogenously added cADPr revealed that the catabolism of cADPr at varying Mg²⁺ and P_i concentrations had only minor relevance for the modulatory effects observed.

To correlate the effects of inorganic phosphate and Mg²⁺ on cADPr-induced Ca²⁺ release observed in the permeabilized cell preparations, measurements of these ions in intact Jurkat T lymphocytes were carried out. Intact Jurkat T cells stimulated via the T cell receptor·CD3 complex did not respond with significant elevation of the free intracellular Mg²⁺ concentration. In contrast, stimulation via the T cell receptor·CD3 complex resulted in an increase in the intracellular inorganic phosphate concentration. These data indicate a role for the intracellular inorganic phosphate concentration in the regulation of cADPr-mediated Ca²⁺ release in T lymphocytes.

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