Fig. 5. Thiol levels in Geukensia demissa gills as a function of Na₂S concentration. Thiols pertaining to the left y-axis are thiosulfate (circles), glutathione (diamonds) and cysteine (upright triangles), connected with solid lines. Thiols pertaining to the right y-axis are sulfide (squares) and sulfite (inverted triangles), connected with broken lines. Lines serve only to connect data points. Values are means ± S.D. (N=3). To eliminate overlap of error bars, some points have been offset by 10 µmol l^-1. Asterisks designate significant difference from the value at 0 µmol l^-1 Na₂S (Bonferroni test). (A) Gills exposed to 0.5 µmol l^-1 5-HT. (B) Gills exposed to 10 µmol l^-1 5-HT.