Fig. 5. Effect of the membrane potential on cell volume changes. (A) Cell volume was measured using ion-sensitive microelectrodes filled with Corning 477317, which monitored the concentration of the volume marker TMA⁺. In parallel, E_m was clamped to a fixed holding potential (here –60 mV) and the clamp current (I_VC) was recorded. Hypotonic conditions (–40 mmol l^–1 NaCl) caused a reversible swelling and a transient outward current, while hypertonic conditions (+40 mmol l^–1 NaCl) caused a reversible shrinkage and a transient inward current. (B) Cell volume changes (Vol_rel) recorded under anisotonic conditions at E_m=–40 to –70 mV. Cell shrinkage did not change significantly with the holding potential, while cell swelling was almost twice as large at –70 mV as at –40 mV (P<0.05). Data are means ± s.d.; number of experiments is given beside the data bars (bar at +40 mmol l^–1 NaCl, –70 mV results from a single experiment).