Figure 2.

Effect of Ca²⁺ free medium, voltage dependent Ca²⁺ channel antagonists and tetrodotoxin on the electrical field stimulation-evoked and ATP-induced outflow of [³H]-NA in the isolated guinea-pig right atrium. The preparations were superfused and subjected to electrical field stimulation (S₁, 25 V cm⁻¹, 2 Hz, 2.5 ms, 240 shocks) or ATP (1 mM) application, according to the experimental protocol shown in Figure 1b. Ca²⁺ free solution (Ca²⁺ free), supplemented with 1 mM EGTA was applied from 60 min before the start of sample collection, and thereafter, ω-conotoxin GVIA (CGTX, 0.1 μM), Cd²⁺ (Cd²⁺, 100 μM) and tetrodotoxin (TTX, 1 μM) was perfused from 10 min before the start of the sample collection period, and thereafter. The net tritium release evoked by electrical field stimulation (EFS, open bars) or ATP (ATP, solid bars) were calculated by the area-under-the-curve method and expressed in fractional release (%). Data show the means±s.e.mean of 6–8 identical experiments. Asterisks indicate significant differences from respective controls, calculated by ANOVA followed by Dunnett test (^**P>0.01). n.d. not detectable.