Frequency dependent α2-adrenoceptor mediated modulation of excitatory junction potentials in guinea-pig mesenteric artery

Abstract

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′-disulfonic acid (PPADS, 30 μM) but persisted following reserpinization. Suramin (100 μM) enhanced EJPs at 0.2–0.5 Hz responses and reduced them at 2–32 Hz. Phentolamine (1 μM) and yohimbine (0.1 μM) enhanced EJPs at 0.2–8 Hz but not at 16–32 Hz. Oxymetazoline (0.3 μM) 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 μM) was without effect at all frequencies in control arteries but reduced EJPs at 0.2–2 Hz in reserpine-treated arteries. In conclusion, pre-junctional α2-adrenoceptors modulate ATP release during low frequency, brief duration sympathetic nerve stimulation.