Frequency dependent alpha(2)-adrenoceptor mediated modulation of excitatory junction potentials in guinea-pig mesenteric artery

Excitatory junctional potentials (EJPs) elicited with brief duration (10 s) electrical field stimulation of guinea-pig mesenteric arteries were nearly abolished at all frequencies by pyridoxal-phosphate-6-azophenyl-2',4'-disu lfonic acid (PPADS, 30 muM) but persisted following reserpinization. Surami n (100 muM) enhanced EJPs at 0.2-0.5 Hz responses and reduced them at 2-32 Hz. Phentolamine (1 muM) and yohimbine (0.1 muM) enhanced EJPs at 0.2-8 Hz but not at 16-32 Hz. Oxymetazoline (0.3 muM) reduced EJPs at 0.2-0.5 Hz but not at 1-32 Hz. Following reserpinization, EJPs were enhanced at 0.2-2 Hz but not at 4-32 Hz. Clonidine (0.1 muM) was without effect at all frequenci es in control arteries but reduced EJPs at 0.2-2 Hz in reserpine-treated ar teries. In conclusion, pre-junctional alpha (2)-adrenoceptors modulate ATP release during low frequency, brief duration sympathetic nerve stimulation. (C) 2001 Elsevier Science B.V. All rights reserved.