title: Temporal relationship between cytosolic free Ca(2+) and membrane potential during hypotonic turgor regulation in a brackish water Charophyte Lamprothamnium succinctum.
abstract: Internodal cells of a brackish water charophyte, Lamprothamnium succinctum, regulate turgor pressure in response to changes in external osmotic pressure by modifying vacuolar concentrations of KCl. An increase in cytosolic concentration of free Ca(2+) ([Ca(2+)](c)) is necessary for the progress of turgor regulation induced by hypotonic treatment. Initial changes in membrane potential and [Ca(2+)](c) upon hypotonic treatment were measured to examine the temporal relationship between the two parameters. Fura-dextran (potassium salt, M(r) 10,000, anionic) that had been injected into the cytosol was used to measure [Ca(2+)](c). Membrane potential and membrane conductance under a current-clamp condition were also measured. Decrease in external osmotic pressure by 0.16 Osm induced a simultaneous increase in [Ca(2+)](c) with both depolarization of the membrane and increase in the membrane conductance. Decrease in external osmotic pressure by 0.05 Osm induced a simultaneous increase in [Ca(2+)](c) with membrane depolarization but the increase in membrane conductance started later than the other two processes. There was a close temporal relationship between the increase in [Ca(2+)](c) and membrane depolarization on the initial response of turgor regulation induced by hypotonic treatment.
mesh_terms: D001692:Biological Transport / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology; D000460:Chlorophyta / Q000166:cytology / Q000502:physiology*; D003595:Cytoplasmic Streaming / Q000502:physiology; D003600:Cytosol / Q000378:metabolism; D007038:Hypotonic Solutions; D017136:Ion Transport / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009997:Osmotic Pressure / Q000187:drug effects; D011189:Potassium Chloride / Q000494:pharmacology; D014867:Water / Q000494:pharmacology / Q000502:physiology*
chemical_list: D007038:Hypotonic Solutions; D014867:Water; D011189:Potassium Chloride; D002118:Calcium