Abstract
Cytochalasins are routinely used to stimulate a variety of functions in eukaryotic cells even though their precise mode of action remains to be elucidated. In the present work we used the fluorescent Ca 2+ indicator quin2 to study the effect of various cytochalasins, cytochalasins A, B, C, D, E (CA, CB, CC, CD, CE) and dihydrocytochalasin B (dhCB) on the intracellular Ca 2+ concentration ([Ca 2+] i ) in various types of leukocytes, viz. neutrophils and lymphocytes. In human neutrophils, cytochalasins increase [Ca 2+] i mainly by releasing Ca 2+ from membrane-bound, intracellular stores. Thus, in order to readily appreciate the effect of cytochalasins on [Ca 2+] i , these cells must be loaded with low intracellular quin2 concentrations. On the other hand, in peripheral blood lymphocytes, splenocytes and thymocytes, the increase in [Ca 2+] i is predominantly due to an increased Ca 2+ influx from the extracellular medium. In addition, we found that in neutrophils these drugs prolong the increase in [Ca 2+] i induced by chemotactic peptides, probably by increasing the cell permeability to Ca 2+. Finally, in thymocytes, cytochalasins potentiate the production of inositol phosphates induced by the polyclonal mitogen concanavalin A (conA).
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