Figure 1.

Influence of db-cGMP (A) and db-cAMP (B) on Ca²⁺-dependent chemiluminescence of aequorin in protoplasts isolated from transgenic tobacco leaves (traces from chart recorder). Applications of stimuli are shown by arrows. Aliquots (200 μL) of cyclic mononucleotides diluted in buffer to a final concentration of 10 μm, were added to the suspension (0.5 mL) of protoplasts (2 × 10⁵ cells mL⁻¹) in 0.5 m mannitol, 20 mm Hepes, pH 7.0, 2 mm MgCl₂, and 0.1 mm EGTA. Before the addition of cyclic mononucleotides, CaCl₂ solution (200 μL) was added to give a final CaCl₂ concentration of 1 mm (shown by arrows). C, Peak [Ca²⁺]_cyt values after the addition of cyclic mononucleotides and Ca²⁺ to protoplasts were calculated after chemiluminescence discharge under the action of 0.1% Triton X-100/100 mm CaCl₂, as described previously (Cobbold and Rink, 1987; Knight and Knight, 1995). Experiments were performed seven times; the error bars on histograms indicate sd.