CALCIUM-RELEASE ACTIVITY AND METABOLISM OF INOSITOL 1,4,5-TRISPHOSPHATE IN T-CELLS - MODULATION BY NOVEL INOSITOL 1,4,S-TRISPHOSPHATE 5-PHOSPHATASE INHIBITORS

Stimulation of the T cell antigen receptor/CD3 complex is followed by phospholipase C activation, phosphoinositol lipid metabolism and ultim ately by a rapid rise in both myo-inositol 1,4,5-trisphosphate [Ins(1, 4,5)P-3] and myo-inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P-4] as well as cytosolic free calcium concentration. A 5-phosphatase plays a pivotal role in the subsequent metabolism of Ins(1,4,5)P-3 and Ins( 1,3,4,5)P-4. Synthetic routes have been developed which have enabled t he synthesis of both natural and unnatural inositol phosphates and thi s approach has yielded several compounds which have been shown to act as inhibitors of Ins(1,4,5)P-3 5-phosphatase. These compounds offer co nsiderable potential for investigation of the complex metabolism and f unction of Ins(1,4,5)P-3 and Ins(1,3,4,5)P-4 in T cell activation and proliferation. We now report the time course and temperature sensitivi ty of Ins(l,4,5)P-3-induced Ca-45(2+) release in the permeabilised leu kaemic T cell line Jurkat. Furthermore, we demonstrate that the metabo lism of Ins(1,4,5)P-3 in the presence of two novel 5-phosphatase inhib itors, namely L-myo-inositol 1,4,5-trisphosphorothioate [L-Ins(1,4,5)P S3] and myo-inositol 1,3,5-trisphosphorothioate [Ins(l,3,5)PS3], can b e inhibited with concomitant elevation of the heparin-sensitive Ins(l, 4,5)P-3-induced release of Ca-45(2+). These novel 5-phosphatase inhibi tors provide a starting point for development of cell-permeable analog ues which may be able to modulate cell function in intact cells and ma y be used as manipulative tools with which to elucidate the function o f Ins(1,4,5)P-3 and Ins(1,3,4,5)P-4 with respect to T cell activation.