2 INDEPENDENTLY REGULATED CA2+ ENTRY MECHANISMS COEXIST IN JURKAT T-CELLS DURING T-CELL RECEPTOR ANTIGEN ACTIVATION

Receptor-mediated Ca2+ influx was studied in the human leukaemic T cell line, Jurkat. Stimulation of these cells through the T cell antigen-receptor complex with OKT3 (an antibody against the CD3 molecules of the T cell antigen-receptor complex), or inhibition of the endoplasmic reticular Ca2+-ATPase with thapsigargin, resulted in Ca2+ mobilization from intracellular stores and the activation of Ca2+ and Mn2+ entry. The rates of thapsigargin-induced Ca2+ and Mn2+ entry in Jurkat cells were 76 % and 64 % respectively of those observed after treatment of these cells with OKT3. The combined addition of thapsigargin plus OKT3 to Jurkat cells produced an enhanced effect on the sustained increase in the cytosolic free Ca2+ concentration that was greater than that obtained by addition of thapsigargin or OKT3 alone. The rates of Ca2+ and Mn2+ entry were increased to 119 % and 112 % respectively of the OKT3-induced rates. Taken together, these results suggest that the inositol 1,4,5-trisphosphate-sensitive Ca2+-pool-dependent bivalent cation entry only accounts for 57 % and 52 % respectively of the total OKT3-dependent Ca2+ and Mn2+ entry, and that the rest is mediated by second messenger(s). Thus two separate pathways coexist in regulating Ca2+ entry in Jurkat cells during activation mediated through the T cell receptor.