B. Driessen et al., NEURAL ATP RELEASE AND ITS ALPHA-2-ADRENOCEPTOR-MEDIATED MODULATION IN GUINEA-PIG VAS-DEFERENS, Naunyn-Schmiedeberg's archives of pharmacology, 348(4), 1993, pp. 358-366
Contractions, release of previously stored [H-3]-noradrenaline (measur
ed as overflow of total tritiated compounds) and release of ATP elicit
ed by electrical field stimulation (210 pulses, 7 Hz) were studied in
the superfused vas deferens of the guinea pig. Prazosin and suramin we
re used to suppress non-neural ATP release, and effects of bromoxidine
and rauwolscine on the neural release thus isolated were examined. El
ectrical stimulation elicited reproducible contraction, tritium overfl
ow and ATP overflow. Both prazosin (0.03 - 3 muM) and suramin (30 - 30
0 muM) reduced contractions as well as the evoked overflow of ATP. No
visible contraction remained in 21 of 28 tissues exposed to prazosin 0
.3 muM combined with suramin 300 muM. The evoked overflow of ATP under
these conditions was about 17% of that observed in the absence of dru
gs. In the presence of prazosin 0.3 muM and suramin 300 muM, bromoxidi
ne (0.01 - 1 muM) decreased and rauwolscine (0.1 - 10 muM) increased t
he evoked overflow of both tritium and ATP. Rauwolscine increased the
evoked overflow of tritium to a significantly greater extent than the
overflow of ATP. It is concluded that the overflow of ATP elicited by
electrical (neural) stimulation in the presence of prazosin 0.3 muM an
d suramin 300 muM reflects purely neural release of ATP. This release
of ATP, like the release of noradrenaline, is modulated through prejun
ctional alpha2-adrenoceptors. The alpha2-adrenoceptor modulation of th
e release of noradrenaline seems to be more marked than the modulation
of the release of ATP.