Abstract
Ionic responses to alteration in external and internal pH were examined in an organism from a marine-like environment. Vacuolar pH (pHv) is about 4.9–5.1, constant at external pH (pHo) 5–8, while cytoplasmic pH (pHc) increases from 7.3 to 7.7. pHc regulation fails above pHo 9, and this is accompanied by failure of turgor regulation. Na+ increases above pHo 9, while K+ and Cl decrease. These changes alone cannot however explain the alterations in turgor. Agents known to affect internal pH are also tested for their effect on ion relations.