[Effect of SH-reagents on Ca2+ level in lymphocyte cytoplasm]

The effect of SH-reagents on cytoplasmic free Ca2+ concentration [( Ca2+]i) in rat thymocytes and B lymphoma Raji cells has been studied by means of fluorescent Ca2+ indicator quin-2. N-ethylmaleimide and ethylmercurythiosalicylate have been found to induce a dose-dependent increase of Ca2+ concentration from about 100 nM in the control cells up to 1000 nM. The effect is weakened with a decrease of the external Ca2+ concentration and is not observed already with Ca2+ concentration in the medium less than 0.2 mM. Reduction of the level of intracellular ATP does not suppress the Ca2+ response to SH-reagents. The effect of SH-reagents is weakened with a decrease of the temperature from 37 to 24 degrees C. Addition of 1 mM Mn2+ or Ca2+ into the standard medium containing 1 mM CaCl2 prevents Ca2+ concentration increase in the cytoplasm under the action of SH-reagents. The conclusion is made that in lymphocytes Ca2+ permeability is regulated by a protein(s) sensitive to the SH-reagent and that a high level of SH-group oxidation is necessary to maintain the low Ca2+ permeability of lymphocyte plasma membrane. Mechanisms of SH-reagents action on the Ca2+ level in the cell are discussed.