Pharmacological activation of the ryanodine receptor in Jurkat T-lymphocytes

1 Recently, we provided evidence for cyclic adenosine 5'-diphosphate-ribose , cADP-ribose, as a second messenger in Jurkat T-lymphocytes upon stimulati on of the T-cell receptor/CD3- complex (Guse et al., 1999). cADP-ribose mob ilizes Ca2+ from an intracellular Ca2+ store which is sensitive to caffeine and gated by the ryanodine receptor/Ca2+ release channel. In the present s tudy we investigated the ability of the trypanocidal drug, suramin, to acti vate the ryanodine receptor of T-cells. Since suramin cannot permeate the p lasma membrane, it was necessary to microinject the drug into Fura-2 loaded T-lymphocytes. 2 In a dose dependent manner suramin increased the intracellular Ca2+ conce ntration. The dose-response curve is very steep and calculates for an EC50 of 7.6 +/- 2.9 mM suramin in the injection pipette. 3 Co-injection of the selective ryanodine receptor inhibitor ruthenium red completely abolished the suramin induced Ca2+ transient. This finding allow s for the conclusion that the IP3-receptor sensitive Ca2+ pool is not the p rimary target of the suramin induced Ca2+ transient. 4 Furthermore, Ins(1,4,6)PS3, an antagonist of the InsP(3)-receptor could n ot suppress the suramin-induced Ca2+ signal. The suramin induced Ca2+ trans ients declined very slowly; however, in the presence of Ins(1,4,6)PS3 this decay was accelerated. In addition, suramin did not interact with the cADP- ribose binding site of the ryanodine receptor of T-cells. 5 In conclusion, suramin is found to be an agonist for the T-cell ryanodine receptor as previously found for the cardiac and skeletal muscle isoform. Therefore, suramin can be designated a universal ryanodine receptor agonist .