RT Journal Article T1 Role of H(+)-pyrophosphatase activity in the regulation of intracellular pH in a scuticociliate parasite of turbot: Physiological effects A1 Mallo Seijas, Natalia A1 Lamas Fernández, Jesús A1 Felipe González, Ana Paula de A1 Sueiro Benavides, Rosa Ana A1 Fontenla Iglesias, Francisco A1 Leiro Vidal, José Manuel K1 Philasterides dicentrarchi K1 Intracellular pH K1 Calcium K1 ATP K1 H+-PPase K1 Osmoregulation AB The scuticociliatosis is a very serious disease that affects the cultured turbot, and whose causal agent is the anphizoic and marine euryhaline ciliate Philasterides dicentrarchi. Several protozoans possess acidic organelles that contain high concentrations of pyrophosphate (PPi), Ca(2+) and other elements with essential roles in vesicular trafficking, pH homeostasis and osmoregulation. P. dicentrarchi possesses a pyrophosphatase (H(+)-PPase) that pumps H(+) through the membranes of vacuolar and alveolar sacs. These compartments share common features with the acidocalcisomes described in other parasitic protozoa (e.g. acid content and Ca(2+) storage). We evaluated the effects of Ca(2+) and ATP on H (+)-PPase activity in this ciliate and analyzed their role in maintaining intracellular pH homeostasis and osmoregulation, by the addition of PPi and inorganic molecules that affect osmolarity. Addition of PPi led to acidification of the intracellular compartments, while the addition of ATP, CaCl2 and bisphosphonates analogous of PPi and Ca(2+) metabolism regulators led to alkalinization and a decrease in H(+)-PPase expression in trophozoites. Addition of NaCl led to proton release, intracellular Ca(2+) accumulation and downregulation of H(+)-PPase expression. We conclude that the regulation of the acidification of intracellular compartments may be essential for maintaining the intracellular pH homeostasis necessary for survival of ciliates and their adaptation to salt stress, which they will presumably face during the endoparasitic phase, in which the salinity levels are lower than in their natural environment PB Elsevier SN 0014-4894 YR 2016 FD 2016-10 LK http://hdl.handle.net/10347/18174 UL http://hdl.handle.net/10347/18174 LA eng NO Mallo N, Lamas J, de Felipe AP, Sueiro RA, Fontenla F, Leiro JM. (2016). Role of H(+)-pyrophosphatase activity in the regulation of intracellular pH in a scuticociliate parasite of turbot: Physiological effects. Exp Parasitol. 169:59-68. doi: 10.1016/j.exppara.2016.07.012 NO This is the accepted manuscript of the following article: Mallo, N., Lamas,J., de Felipe, A.P., Sueiro, R.A., Fontenla, F. & Leiro, J.M. (2016). Role ofH(+)-pyrophosphatase activity in the regulation of intracellular pH in ascuticociliate parasite of turbot: Physiological effects. ExperimentalParasitolology, 169, 59-68. doi: 10.1016/j.exppara.2016.07.012 NO This work was financially supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 634429 (PARAFISHCONTROL),by the Ministerio de Economía y Competitividad (Spain) under grant agreement AGL2014-57125-R and by grant GPC2014/069 from the Xunta de Galicia (Spain) DS Minerva RD 24 abr 2026