Possible role of calmodulin in the secretion of Entamoeba histolytica electron‐dense granules containing collagenase

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Abstract
Summary: Entamoeba histolytica cells secrete electron‐dense granules (EDGs) that have collagenase activity. To study the possible involvement of calmodulin (CaM) on EDG secretion, the effect of several CaM antagonists (TFP, R24571, W‐7, W‐5, dibucaine and DL‐propranolol) was tested on this cellular function. Except for W‐5 and dibucaine, the rest of these compounds inhibited EDG secretion. Transmission electron microscopy of collagen‐activated trophozoites showed numerous EDGs located in or near the surface membrane. In contrast, trophozoites incubated with TFP showed no EDGs. Protein kinase C inhibitors (H‐7, ML‐9) had no effect on EDG secretion, suggesting that CaM antagonists acted by selectively inhibiting CaM. These results suggest that a CaM‐dependent process is involved in EDG secretion.