Figure 2. Influence of the stimulation parameters on the effects of P- and L-type Ca2+ channel blockers and endogenous adenosine on evoked [3H]ACh release from motor nerve terminals.
A and B, show the time course of tritium outflow from electrically stimulated phrenic nerve terminals taken from typical experiments in the absence (Control, ▪) and in the presence of ω-Agatoxin IVA (ω-AgaTx IVA, 0.1 μm, ○) and nifedipine (1 μm, •). Tritium outflow (ordinate) is expressed as a percentage of the total radioactivity present in the tissue at the beginning of the collection period. The abscissa indicates the times at which samples were collected. [3H]ACh release was elicited twice (S1 and S2) by stimulating the phrenic nerve trunk with 750 electrical pulses delivered with frequencies of 5 Hz and 50 Hz; either one train (15 s) (A) or a series of five bursts (3 s, 150 pulses, 20-s interburst interval) (B) were delivered when 50-Hz stimulation was applied. ω-AgaTx IVA (0.1 μm), nifedipine (1 μm) and adenosine deaminase (ADA, 0.5 U ml−1) were applied 15 min before the end of S2, as represented by the horizontal bars. Note that spontaneous tritium outflow was not significantly modified in the presence of the drugs. C, the ordinates are percentage change in S2/S1 ratio in the presence of test drugs as compared with the S2/S1 ratio in control experiments using a similar stimulation protocol. Zero percent represents identity between the two ratios. Each column represents pooled data from n = 4–8 individual experiments. The vertical bars represent s.e.m. *P < 0.05 (one-way ANOVA followed by Dunnett's modified t test) when compared with controls obtained in the absence of test drugs.