Down-regulation of brain muscarinic cholinergic receptor promoted by diacylglycerols and phorbol ester |
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Authors: | M F Pediconi F J Barrantes |
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Institution: | (1) Instituto de Investigaciones Bioquímicas, Consejo Nacional de Investigaciones Científicas y Técnicas and Universidad Nacional del Sur, C. C. 857, 8000 Bahía Blanca, Argentina |
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Abstract: | Sustained agonist stimulation induces an asymmetric down-regulation of brain muscarinic acetylcholine receptor (mAChR): 43±2% in the right and 26±2% in the left cerebral hemisphere, respectively (Ref. 1). In order to determine the possible involvement of endogenous diacylglycerols produced under muscarinic stimulation in the down-regulation phenomenon, here we have studied the effects of synthetic diacylglycerols and a phorbol ester on cells dissociated from rat cerebral cortex. Oleoylacetylglycerol decreased the amount of cell-surface mAChR by 37±2% and 25±2% in right and left cerebral cortex, respectively. Long-term treatment with phorbol dibutyrate also produced internalization of the mAChR (25±1.5% and 33±2% in right and left cortical cells, respectively). These changes occurred without modification of the Kdapp for the selective antagonist pirenzepine. The action of calcium ions was also studied using incubation of cells with the ionophore A23187. No changes were observed in the amount of mAChR detected at the plasma membrane with the ionophore alone, but when used in combination with phorbol dibutyrate and the agonist carbamylcholine a sinergistic decrease in mAChR was apparent. It is concluded that long-term exposure to exogenously added diacyglycerols and phorbol ester significantly reduces the amount of mAChR detected at the plasma membrane and abolishes the asymmetry of the down-regulation phenomenon observed under specific muscarinic stimulation, suggesting that diacylglycerols may be one of the factors responsible for such asymmetry.Abbreviations used A23187
ionophore A23187
- ATRO
atropine
- CARB
carbamoylcholine
- DAG
diacylglycerol
- DMEM
Dulbecco's modified Eagle's medium
- DMSO
dimethylsulfoxide
- HEPES
4-(2-hydroxyethyl)-1-piperazine ethanesulfonic acid) buffer
- PZ
pirenzepine
- LCC
left cerebral cortex
- mAChR
muscarinic acetylcholine receptor
- OAG
oleoylacetylglycerol
- PDB
phorbol dibutyrate
- RCC
right cerebral cortex |
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Keywords: | Brain asymmetry muscarinic receptor distribution M1 muscarinic receptor subtypes downregulation synthetic diacylglycerols phorbol esters |
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