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'-disulfonic acid (PPADS, 30 microM) but persisted following reserpinization. Suramin (100 microM) enhanced EJPs at 0.2-0.5 Hz responses and reduced them at 2-32 Hz. Phentolamine (1 microM) and yohimbine (0.1 microM) enhanced EJPs at 0.2-8 Hz but not at 16-32 Hz. Oxymetazoline (0.3 microM) 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 microM) 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 alpha(2)-adrenoceptors modulate ATP release during low frequency, brief duration sympathetic nerve stimulation.
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Department of Physiology and Cell Biology, Anderson Medical Building/MS 352, University of Nevada School of Medicine, 89557-0046, Reno, NV, USA. vnm@med.unr.edu
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D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008638:Mesenteric Arteries / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology*; D010109:Oxymetazoline / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011732:Pyridoxal Phosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D018341:Receptors, Adrenergic, alpha-2 / Q000502:physiology*; D012110:Reserpine / Q000494:pharmacology; D013498:Suramin / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D018341:Receptors, Adrenergic, alpha-2; C077792:pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid; D015016:Yohimbine; D011732:Pyridoxal Phosphate; D013498:Suramin; D012110:Reserpine; D010109:Oxymetazoline; D003000:Clonidine; D010646:Phentolamine