1 A modified form of the highly specific luciferin-luciferase assay wa
s used to measure the overflow of adenosine 5'-triphosphate (ATP) from
the field-stimulated mouse vas deferens in vitro. Precise timing of t
he stimulation, superfusate collection and assay minimized ATP degrada
tion before assay, offering the opportunity for quantitative studies.
2 Stimulation with between 50 and 200 supramaximal pulses at 5 Hz incr
eased ATP overflow by between 7 and 28 times over basal. 3 ATP overflo
w increased steadily with increasing numbers of stimuli from 50 to 200
pulses. Increasing the frequency of stimulation initially had no effe
ct, but above 10 Hz there was increased overflow, suggesting an intera
ction between facilitated release and the rate of degradation by extra
cellular ATPases.4 Contractions of the vas induced by exogenous (-)-ph
enylephrine produced only a small increas in ATP overflow, suggesting
that the stimulation induced increase in ATP overflow is mostly pre-ju
nctional in orgin, though tetrodotoxin eliminated stimulation-induced
overflow only in a proportion of preparations.