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Fig. 2. Upper tubules were initially stimulated with 25 nmol l–1
5HT in saline and fluid was collected at 10 min intervals for a total of 30
min. The tubules were then maintained in 25 nmol l–1 5HT
(filled triangles) or received 0.1 µmol l–1 of either
RhoprDH31 (filled circles) or leucokinin I (filled squares) at the
solid arrow, and fluid was collected for a further 40 min at 10 min intervals.
The rate of fluid secretion (A) was calculated after measuring the diameter of
each droplet, and ion-selective microelectrodes were used to measure the
K+ (B), Na+ (C) and Cl– (D)
concentration of each droplet of secreted fluid. RhoprDH31 and
leucokinin I had no effect on the rate of fluid secretion or the ion
composition of the secreted fluid. Each point is the mean ± s.e.m. of
7–9 individual tubules. Addition of 1 µmol l–1 5HT
at the dashed arrow was used to confirm the viability of the Malpighian
tubules.