The basic secretagogue compound 48/80 activates G proteins indirectly via stimulation of phospholipase D–lysophosphatidic acid receptor axis and 5-HT1A receptors in rat brain sections
Article first published online: 30 JAN 2009
2006 British Pharmacological Society
British Journal of Pharmacology
Volume 147, Issue 6, pages 596–606, March 2006
How to Cite
Palomäki, V. A. B. and Laitinen, J. T. (2006), The basic secretagogue compound 48/80 activates G proteins indirectly via stimulation of phospholipase D–lysophosphatidic acid receptor axis and 5-HT1A receptors in rat brain sections. British Journal of Pharmacology, 147: 596–606. doi: 10.1038/sj.bjp.0706671
- Issue published online: 30 JAN 2009
- Article first published online: 30 JAN 2009
- (Received September 7, 2005, Revised December 7, 2005, Accepted December 19, 2005)
- Compound 48/80;
- phospholipase D;
- lysophosphatidic acid;
- [35S]GTPγS binding assay;
- 5-HT1A receptor
The basic secretagogues, such as compound 48/80 (c48/80) and mastoparans, are widely used histamine-releasing agents and their mechanism of action is commonly attributed to a direct, receptor-bypassing property to activate the Gi/o class of G proteins.
We tested here whether c48/80 could directly stimulate [35S]guanosine-5′-[γ-thio]triphosphate ([35S]GTPγS) binding to rat brain sections in an attempt to visualize the entire signaling pool of Gi/o in its native neuroanatomical context.
Instead of direct Gi/o activation, c48/80 (100 μg ml−1) from various suppliers stimulated brain phospholipase D (PLD) activity, leading to the generation of endogenous phospholipids capable of activating brain white matter-enriched, Gi/o-coupled lysophosphatidic acid (LPA) receptors. This response was sensitive to 1-butanol and was potently reversed by the LPA1/LPA3 receptor-selective antagonist Ki16425 (IC50 59±13 nM, mean±s.e.m.), and showed age-dependent decline, closely reflecting known developmental regulation of the PLD–LPA1 receptor axis in the CNS.
In addition, c48/80 was found to modestly activate hippocampal 5-HT1A receptors in a pH-dependent and antagonist-sensitive manner.
Consistent with the lack of direct Gi/o-activating properties in brain sections, c48/80 showed no activity in classical membrane [35S]GTPγS binding assays. Instead, c48/80 from one particular manufacturer elicited non-specific effect in these assays, therefore challenging the previous interpretations regarding the compound's ability to activate G proteins directly.
We conclude that c48/80 is not a receptor-bypassing general G protein activator but rather activates PLD, leading to generation of endogenous LPA receptor-activating phospholipids. This property may also contribute to the compound's ability to release histamine from mast cells.
British Journal of Pharmacology (2006) 147, 596–606. doi:10.1038/sj.bjp.0706671