POSSIBLE ROLE OF CALMODULIN IN EXCYSTATION OF GIARDIA-LAMBLIA

The protozoan Giardia lamblia initiates infection when trophozoites em erge from a cyst in the hosts by the excystation process. Although thi s process is crucial to the initiation of infection by G. lamblia, lit tle is known about its regulation. To study the possible involvement o f calmodulin (CaM) in excystation we tested the effect of several CaM antagonists (TFP, W-7, and W-5) on this cellular function. Except for W-5 the rest of these compounds inhibited excystation. The protein kin ase C inhibitor H-7 had no effect on excystation, suggesting that CaM antagonists acted by selectively inhibiting CaM. Furthermore, CaM was redistributed after the induction of excystation and there was an incr ease in its fluorescence and activity. These results suggest that a Ca M-dependent process is involved in C. lamblia excystation.