Intracellular calcium release mediated by noradrenaline and acetylcholine in mammalian pineal cells

J Pineal Res. 1996 Aug;21(1):15-28. doi: 10.1111/j.1600-079x.1996.tb00266.x.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetylcholine / pharmacology*
  • Adrenergic alpha-Agonists / pharmacology*
  • Adrenergic beta-Antagonists / pharmacology
  • Animals
  • Calcium / metabolism*
  • Cells, Cultured
  • Cholinergic Agonists / pharmacology*
  • Female
  • Fluorescent Dyes / metabolism
  • Fura-2 / metabolism
  • Male
  • Microspectrophotometry
  • Muscarinic Agonists / pharmacology
  • Norepinephrine / pharmacology*
  • Pineal Gland / cytology
  • Pineal Gland / drug effects
  • Pineal Gland / metabolism*
  • Rats
  • Rats, Wistar

Substances

  • Adrenergic alpha-Agonists
  • Adrenergic beta-Antagonists
  • Cholinergic Agonists
  • Fluorescent Dyes
  • Muscarinic Agonists
  • Acetylcholine
  • Calcium
  • Fura-2
  • Norepinephrine