Effects of selected transmitters on free cytosolic calcium concentration and pyruvate dehydrogenation in primary cultures of mouse astrocytes

Description

To study the effects of neurotransmitters on [Ca²⁺]_i and oxidative metabolism of pyruvate, selected adrenergic, serotonergic, purinergic and peptidergic agonists were chosen. Experiments were conducted using the fluorescent calcium indicator, indo-1/AM, to examine changes in [Ca<sup>2+,/sup>]_i and [1-¹⁴C] pyruvate to measure rates of labeled CO₂ formation from pyruvate dehydrogenation. The adrenergic agonist noradrenaline induced an increase in [Ca²⁺]_i via activation of both á₁ and á</sub>2</sub> receptors as both phenylephrine (á₁ agonist) and clonidine (á₂ agonist) caused an elevation in [Ca²⁺]_i level. The increase in [Ca²⁺]_i evoked by either noradrenaline or phenylephrine was inhibited by inclusion of phentolamine (a nonspecific á-antagonist). Yohimbine, an á₂-antagonist, inhibited both noradrenaline- and clonidine-evoked increases in [Ca²⁺]_i, indicating the existence of a population of á₂-adrenoceptors in cultured astrocytes. Noradrenaline also enhanced dehydrogenation of pyruvate to acetyl-CoA. Clonidine exerted a stimulation on pyruvate dehydrogenation and there was a tendency towards a small stimulation by phenylephrine. In contrast, CO₂ formation was not increased when the potassium concentration was raised above 5 mM. Noradrenaline-induced stimulation of flux from pyruvate to acetylCoA was abolished in the absence of extracellular calcium (combined with an elevation of the magnesium concentration or a calcium chelator, EGTA), suggesting that the effect is calcium-dependent. Exposure to dexmedetomidine, a highly specific á₂-adrenergic agonist, led to a biphasic increase in [Ca²⁺]_i and in pyruvate oxidation. The effect was inhibited both by yohimbine and idazoxan. Chronic treatment with 1 mM lithium chloride decreased noradrenaline-induced increase in [Ca<sup>2+,/sup>]_i. This is in agreement with the assumption that lithium impairs the turnover in the inositol phosphate (IP) cycle. Serotonin caused an increase of [Ca²⁺]_i in concentrations between 10 pM and 10 ìM in dibutyryl cyclic adenosine 3',5'-monophosphate (dBcAMP) treated astrocytes by stimulating 5HT_2C and/or 5-HT_2A receptors. Micromolar concentrations of serotonin were required for activation of the 5-HT_2A receptor, whereas low nanomolar concentrations stimulated the 5-HT_2C receptor. Fluoxetine, an antidepressant acting like 5-HT, exerted an agonist effect on [Ca²⁺]_i in astrocytes. Adenosine and guanosine, purinergic agonists, evoked significant increases in [Ca²⁺]_i, an effect that was not blocked by P₁ antagonists. Arginine vasopressin (AVP) induced increases in [Ca²⁺]_i which could be abolished by a V₁-selective antagonist but not by removal of extracellular Ca²⁺. However, AVP failed to affect pyruvate oxidation in astrocytes.

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1. http://library.usask.ca/theses/available/etd-10212004-000121

Tags

pharmacology

Additional Fields

Identifer	oai:union.ndltd.org:USASK/oai:usask.ca:etd-10212004-000121
Date	01 January 1996
Creators	Chen, Ye
Contributors	Hertz, Leif
Publisher	University of Saskatchewan
Source Sets	University of Saskatchewan Library
Language	English
Detected Language	English
Type	text
Format	application/pdf
Source	http://library.usask.ca/theses/available/etd-10212004-000121
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