A CAFFEINE RYANODINE-SENSITIVE CA2+ POOL IS INVOLVED IN TRIGGERING SPONTANEOUS VARIATIONS OF CA2+ IN JURKAT T-LYMPHOCYTES BY CA2+-INDUCED CA2+ RELEASE (CICR) MECHANISM/

Caffeine and ryanodine triggered an increase in [Ca2+](i) (73 +/- 22 a nd 61 +/- 18 nM, respectively) in Jurkat: cell populations that was in dependent of external Ca2+. In individual cells, caffeine and ryanodin e induced Ca2+ spikes. Jurkat cell populations initially exposed to ca ffeine did not respond further to ryanodine and vice versa, suggesting an overlap of the Ca2+ pool that was contained within the thapsigargi n sensitive Ca2+ reserve. [H-3]ryanodine bound to a single class of si tes of Jurkat microsomes (K-D, 18.4 +/- 5.7 nM; B-max 24.3 +/- 7.7 fmo l/mg protein). Photolytic release (Nitr5) of caged Ca2+ induced a time -dependent increase of Ca2+ in individual Jurkat cells. The profile of the release of Ca2+ was characterized, 1) by a kinetic (0.55 +/- 0.07 nM s(-1)) slower than the Ca2+ response to caffeine (3.93 +/- 0.66 nM s(-1)) or to ryanodine (3.96 +/- 0.94 nM s(-1)), 2) by a release of C a2+ (131 +/- 43 nM) that slowly returned to baseline and during which low amplitude oscillations were present (room temperature) or Ca2+ spi kes (37 degrees C) and, 3) by a lack of dependency on an influx of Ca2 +. Inhibitors of CICR (ruthenium red and 1-octanol) prevented the phot olysis dependent increase in [Ca2+](i) but not the InsP3-dependent Ca2 + response. Our data suggest that Jurkat T cells possess at least two Ca2+ pools, one that is sensitive to InsP3 and one that is insensitive . These two Ca2+ pools may be involved in a CICR that generates sponta neous Ca2+ spikes and oscillations in these cells. (C) 1997 Elsevier S cience Inc.