Fig. 5. Effect of 5-hydroxytryptamine (5-HT) and ionomycin on ciliary beat frequency (CBF) in pedal, dorsolateral and scattered single ciliary cells. Perfusion with 100 µmol l^–1 5-HT resulted in an approximate doubling in the rate of ciliary beating in pedal (A), fura dextran-loaded pedal (B) and dorsolateral (C) ciliary cells. This 5-HT-stimulated increase in CBF was statistically significant in all cases. The CBF partially recovered when cells were perfused for 5 min with Helisoma saline (HS), whereas perfusion with 10 mmol l^–1 ionomycin further stimulated CBF in pedal (A), fura dextran-loaded pedal (B) and dorsolateral (C) ciliary cells. The scattered single ciliary cells did not display cilio-excitatory responses to 5-HT or ionomycin (D). Measurements were taken once every minute, N=6 cells for A, C and D and N=4 cells for B. Dotted lines represent the time when the specified treatments were initiated.