Figure 1.

Forskolin augments [Ca²⁺]_i changes induced by low 5-HT concentrations in Calliphora salivary gland cells. (A) Stimulation with 3 nM 5-HT produces intracellular Ca²⁺ oscillations. Application of 100 μM forskolin converts oscillatory [Ca²⁺]_i changes into a sustained increase (n = 8). (B) Stimulation of the gland with 30 nM 5-HT, a concentration that saturates fluid secretion, produces a biphasic Ca²⁺ response consisting of an initial transient followed by a plateau of elevated [Ca²⁺]_i. The sustained phase of elevated [Ca²⁺]_i is not effected by forskolin (n = 4). (C) Application of a threshold concentration of 5-HT (1 nM) in Ca²⁺-free PS (0-Ca, 2 mM EGTA) increases [Ca²⁺]_i just measurably without triggering Ca²⁺ spikes. Additional application of 100 μM forskolin induces a transient Ca²⁺ elevation, showing that forskolin augments 5-HT-induced Ca²⁺ release, not Ca²⁺ entry (n = 8).