Ca2+- and glycoconjugates-dependent prey capture in the heliozoon Actinophrys sol

Exocytosis of extrusomes, secretory granules found in protozoa, is involved in prey capture by the heliozoon Actinophrys sol. Here, we show that extracellular Ca2+ is necessary for exocytosis and prey capture in A. sol. We found that A. sol could not capture prey cells in a Ca2+-free solution. L-type Ca2+ channel blockers and a calmodulin antagonist also inhibited the capture of prey. These results suggest that Ca2+ influx via L-type Ca2+ channels plays a crucial role in exocytosis in A. sol. Concanavalin A (Con A) also inhibited prey capture, and the inhibition was relieved by the addition of its hapten sugar, α-mannoside, suggesting that Con A-binding glycoconjugates are implicated in exocytosis of extrusomes and the adhesion of prey cells.