Electrochemical and electrophysiological characterization of neurotransmitter release from sympathetic nerves supplying rat mesenteric arteries

1 Characteristic features of noradrenaline (NA) and adenosine 5'-triphospha te (ATP) release from postganglionic sympathetic nerves in rat small mesent eric arteries in vitro have been investigated on an impulse-by-impulse basi s. NA release was measured using continuous amperometry and ATP release was monitored by intracellular recording of excitatory junction potentials (e. j.ps). 2 Electrical stimuli evoked transient increases in oxidation current. Durin g trains of ten stimuli at 0.5-4 Hz there was a depression in the amplitude of oxidation currents evoked following the first stimulus in the train. 3 The neuronal NA uptake inhibitor, desmethylimipramine (1 mu M), increased the amplitude of the summed oxidation current evoked by ten stimuli at 1 H z and slowed the decay of oxidation currents evoked by trains of ten stimul i at 1 and 10 Hz. 4 The alpha(2)-adrenoceptor antagonist, idazoxan (1 mu M), increased the am plitudes of the oxidation currents evoked during trains of ten stimuli at 0 .5-10 Hz but had no effect on the oxidation currents evoked by the first st imulus in the train. 5 Idazoxan (1 mu M) increased the amplitude of all e.j.ps evoked during tra ins of stimuli at 0.5 and I Hz. In addition, the facilitatory effect of ida zoxan on e.j.ps was significantly greater than that on oxidation currents. 6 The findings indicate that NA release from sympathetic nerves supplying s mall mesenteric arteries is regulated by activation of presynaptic alpha(2) -adrenoceptors and that clearance of released NA in this tissue depends, in part, upon neuronal uptake. The different effects of idazoxan on the oxida tion currents and e.j.ps may indicate that the release of NA and ATP is dif ferentially modulated.