Presynaptic alpha 2-adrenoceptors inhibit calcium influx in terminals of chicken sympathetic neurons and noradrenaline release evoked by nicotinic stimulation.
The changes of intracellular calcium concentration evoked by stimulation of nicotinic receptors and its modulation by alpha 2-adrenoceptors were investigated in chicken sympathetic neurons grown in culture. Stimulation of nicotinic receptors increased the intracellular calcium both in the area of cell bodies and processes. In normal extracellular calcium (1.3 mmol/l), the specific alpha 2-adrenoreceptor agonist UK 14,304 (10 mumol/l) diminished the response in cell bodies but not in processes. The same treatment in medium with reduced calcium (0.13 mmol/l) resulted in the decrease of the response evoked by nicotinic stimulation in the area of processes but not in the cell bodies. The effect of UK 14,304 on evoked noradrenaline release paralleled its influence on intracellular calcium in processes. These data indicate that nicotine stimulation-induced influx of calcium is inhibited by alpha 2-adrenoceptor stimulation both in cell bodies and in processes. It is concluded that the nicotinic stimulation-evoked release of noradrenaline is triggered by influx of calcium through alpha 2-adrenoreceptor sensitive as well as insensitive pathways.
Dolezal
V
V
Institut für Pharmakologie und Toxikologie, Universität Freiburg, Germany.
Schobert
A
A
Heldt
R
R
Hertting
G
G
D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000818:Animals; D000068438:Brimonidine Tartrate; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D002642:Chick Embryo; D004246:Dimethylphenylpiperazinium Iodide / Q000494:pharmacology; D005470:Fluorometry; D016257:Fura-2; D009411:Nerve Endings / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D018722:Nicotinic Agonists / Q000494:pharmacology*; D009638:Norepinephrine / Q000378:metabolism*; D011810:Quinoxalines / Q000494:pharmacology; D013268:Stimulation, Chemical; D013564:Sympathetic Nervous System / Q000378:metabolism*
D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D018722:Nicotinic Agonists; D011810:Quinoxalines; D000068438:Brimonidine Tartrate; D004246:Dimethylphenylpiperazinium Iodide; D002118:Calcium; D016257:Fura-2; D009638:Norepinephrine