Fig. 3. Necturus erythrocytes loaded with fluo-4 (10 µM) and exposed to UV light emitted from a mercury vapor bulb and filtered through a FITC cube (400x). (A) Cells display little fluorescence under isosmotic conditions (n=6). (B) Addition of A23187 (0.5 µM) to the extracellular medium increased fluorescence under isosmotic conditions (n=6). (C) Exposure to a hypotonic (0.5x) Ringer solution increased fluorescence compared to basal conditions (n=6). (D) A low Ca²⁺ hypotonic Ringer solution (5 mM EGTA) did not display the level of fluorescence normally observed following hypotonic swelling (n=6).