Regulation of OX 1 orexin/hypocretin receptor‐coupling to phospholipase C by Ca 2+ influx
Background and purpose: Orexin (OX) receptors induce Ca 2+ elevations via both receptor‐operated Ca 2+ channels (ROCs) and the “conventional” phospholipase C (PLC)–Ca 2+ release–store‐operated Ca 2+ channel (SOC) pathways. In this study we assessed the ability of these different Ca 2+ influx pathway...
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Published in | British journal of pharmacology Vol. 150; no. 1; pp. 97 - 104 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
29.01.2009
|
Online Access | Get full text |
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Summary: | Background and purpose:
Orexin (OX) receptors induce Ca
2+
elevations via both receptor‐operated Ca
2+
channels (ROCs) and the “conventional” phospholipase C (PLC)–Ca
2+
release–store‐operated Ca
2+
channel (SOC) pathways. In this study we assessed the ability of these different Ca
2+
influx pathways to amplify OX
1
receptor signalling to PLC in response to stimulation with the physiological ligand orexin‐A.
Experimental approach:
PLC activity was assessed in CHO cells stably expressing human OX
1
receptors.
Key results:
Inhibition of total Ca
2+
influx by reduction of the extracellular [Ca
2+
] to 1 μM effectively inhibited the receptor‐stimulated PLC activity at low orexin‐A concentrations (by 93% at 1 nM), and this effect was gradually reduced by higher orexin‐A concentrations. A similar but weaker inhibitory effect (84% at 1 nM) was obtained on depolarization to ∼0 mV, which disrupts most of the driving force for Ca
2+
entry. The inhibitor of the OX
1
receptor‐activated ROCs, tetraethylammonium chloride (TEA), was somewhat less effective than the reduction in extracellular [Ca
2+
] at inhibiting PLC activation, probably because it only partially blocks ROCs. The partial inhibitor of both ROCs and SOCs, Mg
2+
, and the SOC inhibitors, dextromethorphan, SKF‐96365 (1‐[β‐(3‐(4‐methoxyphenyl)propoxy)‐4‐methoxyphenethyl]‐1H‐imidazole HCl) and 2‐APB (2‐aminoethoxydiphenyl borate), inhibited PLC activity at low concentrations of orexin‐A, but were not as effective as TEA.
Conclusions and implications:
Both ROCs and SOCs markedly amplify the OX
1
receptor‐induced PLC response, but ROCs are more central for this response. These data indicate the crucial role of ROCs in orexin receptor signalling.
British Journal of Pharmacology
(2007)
150
, 97–104. doi:
10.1038/sj.bjp.0706959 |
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ISSN: | 0007-1188 1476-5381 |
DOI: | 10.1038/sj.bjp.0706959 |