Site(s) and ionic basis of α‐autoinhibition and facilitation of [ 3 H]noradrenaline secretion in guinea‐pig vas deferens

1 The effect of dopamine receptor activation on electrically-or high K+ (30 mM)-evoked neurotransmitter release and rise in intracellular Ca2" concentration was investigated using slices of guinea-pig neostriatum. 6 When the slices were superfused with the Ca2+-free medium containing EGTA (10-M) for 5 min, the rise in [Ca2+i] was markedly suppressed to 18.0% of control by LY-171555 (10-6 M). 7 These data indicate that activation of the D2-dopamine receptor suppresses the elevation of [Ca2+]i induced by depolarizing stimuli. This may be due to inhibition of mobilization of Ca2+ from the intracellullar store. We propose that the D2-receptor-mediated inhibition of transmitter release is probably due to a reduction in intracellular Ca2+ mobilization.

Section: Discussionmentioning

confidence: 99%

D₂‐dopamine receptor‐mediated inhibition of intracellular Ca²⁺ mobilization and release of acetylcholine from guinea‐pig neostriatal slices

Fujiwara

Kato

Shuntoh

et al. 1987

“…[3WH-NA overflow Alberts et al (1981). Previous investigations in rodent vas deferens have shown that [3H]-NA is the major constituent of the total radioactivity released upon stimulation of the tissue (Beattie et al, 1986;Kapocsi et al, 1987).…”

Section: Superfusion Studiesmentioning

confidence: 99%

Neuropeptide Y neuromodulation of sympathetic co‐transmission in the guinea‐pig vas deferens

Ellis

Burnstock

1990

by 50% at 20 pulses and had little effect on preparations stimulated for 240 pulses. 5 Our study suggests that NPY neuromodulates co-transmission in the vas deferens by inhibiting the release of ATP and NA and that these effects predominate over the postjunctional enhancement by NPY. These results also show that the physiological effect of NPY will be determined both by the frequency at which the nerves are discharging and the duration of their firing.

“…Under these conditions, it has previously been shown that over 90% of the tritium present in the tissue after superfusion with Krebs solution is intact [3H]-NA (Alberts et al, 1981). The superfusate was collected in 2-min fractions.…”

Section: Electrophysiological Experimentsmentioning

confidence: 99%

Actions of α, β‐methylene ATP and 6‐hydroxydopamine on sympathetic neurotransmission in the vas deferens of the guinea‐pig, rat and mouse: support for co‐transmission

Allcorn

Cunnane

Kirkpatrick

1986

115

α‐Adrenoceptor antagonists (prazosin or phentolamine) reduced the contractile response to field stimulation of the isolated vasa deferentia of guinea‐pig, rat and mouse. α, β‐Methylene ATP (α, β‐MeATP) reduced that portion of the contraction which was resistant to α‐adrenoceptor blockade. α, β‐MeATP (1–800 μM) did not affect action potential conduction in the guinea‐pig vas deferens nerves, and (up to 10 μM) did not reduce the stimulation‐evoked overflow of [3H]‐noradrenaline from this tissue. Spontaneous excitatory junction potentials (s.e. j.ps) in the majority of cells of guinea‐pig, rat, and mouse vasa were abolished by α, β‐MeATP (0.1–10 μM). In a small number of cells s.e.j.ps were resistant to the actions of α, β‐MeATP (10 μM). Excitatory junction potentials (e.j.ps) in the majority of cells in vasa of all species studied were abolished by α, β‐MeATP (1–10 μM). E.j.ps elicited in some ‘resistant’ cells demonstrated marked facilitation characteristics. It is concluded that α, β‐MeATP inhibits s.e.j.ps and e.j.ps by a postjunctional action. In all species pretreatment of animals with 6‐hydroxydopamine produced a marked reduction in noradrenaline (NA) content (as determined by fluorescence histochemistry) and abolished e.j.ps, findings which suggest that e.j.ps originated from sympathetic nerves. The results support the hypothesis that NA and ATP are co‐transmitters in the sympathetic nerves of rodent vasa.