DEXTRAN SULFATE INDUCES CHANGES IN THE FREE INTRACELLULAR CALCIUM-ION CONCENTRATION OF A SUBPOPULATION OF IMMATURE THYMOCYTES

Previous studies have shown that certain Sulfated polysaccharides. such as dextran sulfate (DxS), can induce a rapid and sustained increase in the free intracellular calcium ion concentration ([Ca2+]i) of thymocytes, whereas they cannot induce a change in the [Ca2+]i of peripheral lymphocytes. This study examined this phenomenon in more detail and clearly demonstrated that only immature thymocytes can respond to DxS. Cortisone-resistant thymocytes failed to exhibit an increase in [Ca2+]i when exposed to DxS. Furthermore, analysis of [Ca2+]i changes at the single cell level using a flow cytometer demonstrated that only a subpopulation of immature thymocytes responded to DxS. Additional flow cytometry studies revealed that DxS and Con-A induce [Ca2+]i response in different subpopulations of thymocytes, approximately 30% of thymocytes responding to Con-A and 15-20% to DxS. Thus. responsiveness to Con-A and DxS, in terms of increases in [Ca2 +/-]i, may represent a novel marker for two different thymocyte subpopulations. Such metabolic markers could be used to complement the conventional serological methods currently employed to define stages in thymocyte differentiation.