INTRACELLULAR CA2+ REGULATION IN CD3 STIMULATED JURKAT T-CELLS INVOLVES H+ FLUXES

Triggering the CD3/TCR complex of T lymphocytes induces a rapid rise in cytosolic free calcium followed by a slowly declining plateau. The level of this plateau depends on external pH, the more alkalinized media leading to higher values. Neither a pH-dependent binding of mAb, nor a perturbation of internal pH can account for this effect. In a sodium-free medium, or in the presence of dimethylamiloride Ca2+, elevation is accompanied by an acidification of the cells; both of them depend, to the same extent, on external calcium concentration. TPA inhibits CD3-, but not ionomycin-induced Ca2+ and H+ raises, indicating that it acts more probably on Ca2+ influx, rather than on its efflux. These results suggest that intracellular calcium could be regulated by a Ca2+/H+ ATPase which drives H+ in and Ca2+ out. In the presence of external Na+, H+ should return to the medium by the Na+/H+ exchanger.