The effect of sulfated polysaccharides on the free intracellular calcium ion concentration of lymphocytes

Abstract

Recent studies have demonstrated that murine lymphocytes express specific cell-surface receptors for a range of sulfated polysaccharides. In order to determine whether polysaccharide binding induces transmembrane signaling, the effects of sulfated polysaccharides on the free intracellular calcium ion concentration ([Ca 2+] i) of mouse thymocytes and spleen cells were determined. Cells were loaded with Indo-I, a fluorescent indicator of calcium ion concentration. The validity and limitations in the use of this indicator in the determination of [Ca 2+] i are documented. Dextran sulfate ( M n = 500 000), ι-carrageenan, λ-carrageenan and κ-carrageenan all cause relatively large changes in the [Ca 2+] i of thymocytes (change in [Ca 2+] i > 50 nM). Of these, dextran sulfate ( M n = 500 000) always had the greatest effect on [Ca 2+] i. Smaller responses were obtained with heparin and dextran sulfate ( M n = 5000), while no response was obtained with chondroitin 4-sulfate, chondroitin 6-sulfate, pentosan sulfate or fucoidin. This response pattern (with the exception of fucoidin and pentosan sulfate) corresponds with the expression of thymocyte receptors for these polysaccharides. The increase in [Ca 2+] i caused by the sulfated polysaccharides requires extracellular Ca 2+ ions however, it is unlikely that voltage-dependent ion channels are involved in these responses. In contrast to thymocytes, although spleen cells express receptors for sulfated polysaccharides, they were unresponsive to all of the sulfated polysaccharides tested, suggesting a basic difference between thymocytes and peripheral T and B lymphocytes in their response to the binding of sulfated polysaccharides.