Role of Ca2+ and cAMP in a cell signaling pathway for resting cyst formation of ciliated protozoan Colpoda cucullus

Abstract

Resting cyst formation (encystment) of Colpoda cucullus is caused by an increase in an external Ca2+ concentration or overpopulation of Colpoda vegetative cells. The Ca2+-mediated or overpopulation-mediated encystment was suppressed by Ca2+ channel blockers (Cd2+, La3+, Ni2+), Ca2+-chelating reagents (EGTA, BAPTA), calmodulin antagonists (W-7, trifluoperazine), Rp-cAMPS (an cAMP analog antagonist) and 2’-deoxyadenosine (a P-site inhibitor of adenylate cyclase). On the other hand, by the addition of Ca2+ ionophore A23187, IBMX (an inhibitor of phosphodiesterase), cAMP or its membrane-permeable derivative, the encystment was prominently induced even in the Ca2+-free medium. These results suggest that Colpoda encystment may be mediated by an increase in cAMP concentration through the activation of adenylate cyclase whose activity is possibly regulated by Ca2+/calmodulin