Fig. 6. Effect of 5-hydroxytryptamine (5-HT) and ionomycin on intracellular Ca²⁺ concentration ([Ca²⁺]_i) in pedal ciliary cells. Pedal ciliary cells were microinjected with fura-2 dextran and imaged once every 15 s. Application of 100 µmol l^–1 5-HT generated two different [Ca²⁺]_i profiles – an early peak in [Ca²⁺]_i followed by a sustained plateau (A; N=5 cells) or a gradual rise in [Ca²⁺]_i over the course of drug application (B; N=5 cells). In both cases, the [Ca²⁺]_i did not recover within 5 min of exposure to Helisoma saline (HS), whereas 10 µmol l^–1 ionomycin stimulated a large increase in the [Ca²⁺]_i. The inset in A shows the experiment on a different scale to illustrate the magnitude of the increase in [Ca²⁺]_i in response to ionomycin application. Dotted lines represent the time when the specified treatments were initiated.