Intracellular calcium release mediated by noradrenaline and acetylcholine in mammalian pineal cells.
The effects of noradrenergic and cholinergic receptor agonists on intracellular Ca2+ concentration ([Ca2+]i) in single dissociated rat pineal cells were investigated by microfluorimetric measurements in Fura-2 acetoxymethyl ester (Fura-2/AM) loaded cells. Noradrenaline (NA) evoked characteristic biphasic increments of intracellular Ca2+ consisting of one or more leading spikes followed by a plateau, resulting from the release of Ca2+ from intracellular stores and from the influx of Ca2+ from the external medium, respectively. This response was reproduced by the alpha 1-adrenoceptor agonist, phenylephrine (PE), in the presence of the beta-adrenoceptor antagonist, propranolol, and was abolished when NA or PE was applied in conjunction with the alpha 1-adrenoceptor antagonist, prazosin. The curve relating the peak amplitude of the Ca2+ increments to different PE concentrations (0.5-10 microM) showed a half-maximum response at 0.6 microM PE, and saturation at concentrations greater than 2 microM. Acetylcholine (ACh) also elicited transient Ca2+ increments consisting of an abrupt rise to a maximum value which decayed exponentially to the basal Ca2+ level. A half-maximum response was achieved at 59 microM ACh. The muscarinic cholinergic receptor agonist, carbachol (CCh), similarly activated Ca2+ increments while the muscarinic antagonist, atropine, abolished them. In the absence of extracellular Ca2+, repetitive stimuli with either alpha 1-adrenergic and muscarinic agonists produced a progressive decrement in the amplitude of the Ca2+ signals because of the depletion of intracellular stores. However, extinction of the response to muscarinic agonists did not preclude a response to adrenergic agonists, while the contrary was not true. These results suggest that these agonists liberate Ca2+ from two functionally distinct, caffeine-insensitive, Ca2+ intracellular stores.
Marín
A
A
Departamento de Fisiología Médica y Biofísica, Facultad de Medicina, Universidad de Sevilla, Spain.
Ureña
J
J
Tabares
L
L
D000109:Acetylcholine / Q000494:pharmacology*; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D018679:Cholinergic Agonists / Q000494:pharmacology*; D005260:Female; D005456:Fluorescent Dyes / Q000378:metabolism; D016257:Fura-2 / Q000378:metabolism; D008297:Male; D015591:Microspectrophotometry; D018721:Muscarinic Agonists / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology*; D010870:Pineal Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D000316:Adrenergic alpha-Agonists; D000319:Adrenergic beta-Antagonists; D018679:Cholinergic Agonists; D005456:Fluorescent Dyes; D018721:Muscarinic Agonists; D000109:Acetylcholine; D002118:Calcium; D016257:Fura-2; D009638:Norepinephrine