BETA-ADRENOCEPTOR-MEDIATED FACILITATION OF NORADRENALINE AND ADENOSINE 5'-TRIPHOSPHATE RELEASE FROM SYMPATHETIC-NERVES SUPPLYING THE RAT TAIL ARTERY

1 The effects of prejunctional beta-adrenoceptor activation on electri cally evoked noradrenaline (NA) and adenosine 5'-triphosphate (ATP) we re studied by use of continuous amperometry and conventional intracell ular recording techniques. Excitatory junction potentials (e.j.ps) wer e used as a measure of ATP release, and NA-induced slow depolarization s and oxidation currents as measures of NA release, from postganglioni c sympathetic nerves innervating the rat tail artery in vitro. 2 Isopr enaline (0.1 mu M) increased the amplitude of e.j.ps, slow depolarizat ions and oxidation currents evoked by short trains of stimuli at 1 to 4 Hz. The facilitatory effect of isoprenaline on e.j.ps and oxidation currents was most pronounced on responses evoked by the first stimulus in a train. 3 Isoprenaline (0.1 mu M) did not detectably alter the am plitude-frequency distribution of spontaneous e.j.ps. 4 The facilitato ry effect of isoprenaline on e.j.ps, slow depolarizations and oxidatio n currents was abolished by the beta-adrenoceptor antagonist, proprano lol(0.1 mu M). Propranolol alone had no effect on e.j.ps, slow depolar izations or oxidation currents. 5 Thus, activation of prejunctional be ta-adrenoceptors increases the release of both NA and ATP from postgan glionic sympathetic nerves. The findings are consistent with the hypot hesis that NA and ATP are released from the same population of nerve t erminals and presumably from the same vesicles.