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.
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 G(i/o) class of G proteins. We tested here whether c48/80 could directly stimulate [(35)S]guanosine-5'-[gamma-thio]triphosphate ([(35)S]GTPgammaS) binding to rat brain sections in an attempt to visualize the entire signaling pool of G(i/o) in its native neuroanatomical context. Instead of direct G(i/o) activation, c48/80 (100 microg 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, G(i/o)-coupled lysophosphatidic acid (LPA) receptors. This response was sensitive to 1-butanol and was potently reversed by the LPA(1)/LPA(3) receptor-selective antagonist Ki16425 (IC(50) 59+/-13 nM, mean+/-s.e.m.), and showed age-dependent decline, closely reflecting known developmental regulation of the PLD-LPA(1) receptor axis in the CNS. In addition, c48/80 was found to modestly activate hippocampal 5-HT(1A) receptors in a pH-dependent and antagonist-sensitive manner. Consistent with the lack of direct G(i/o)-activating properties in brain sections, c48/80 showed no activity in classical membrane [(35)S]GTPgammaS 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.
Palomäki
Ville A B
VA
Department of Physiology, University of Kuopio, POB 1627, FIN-70211 Kuopio, Finland. Ville.Palomaki@uku.fi
Laitinen
Jarmo T
JT
D000818:Animals; D001345:Autoradiography; D001921:Brain / Q000187:drug effects* / Q000201:enzymology; D004340:Drug Contamination; D004789:Enzyme Activation; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006636:Histamine Release; D006863:Hydrogen-Ion Concentration; D007555:Isoxazoles / Q000494:pharmacology; D008297:Male; D008407:Mast Cells / Q000187:drug effects / Q000201:enzymology; D010739:Phospholipase D / Q000378:metabolism*; D011422:Propionates / Q000494:pharmacology; D051381:Rats; D044282:Receptor, Serotonin, 5-HT1A / Q000187:drug effects* / Q000378:metabolism; D049368:Receptors, Lysophosphatidic Acid / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015398:Signal Transduction; D013462:Sulfur Radioisotopes; D003189:p-Methoxy-N-methylphenethylamine / Q000737:chemistry / Q000494:pharmacology*
C477898:3-(4-(4-((1-(2-chlorophenyl)ethoxy)carbonyl amino)-3-methyl-5-isoxazolyl) benzylsulfanyl) propanoic acid; D007555:Isoxazoles; D011422:Propionates; D049368:Receptors, Lysophosphatidic Acid; D013462:Sulfur Radioisotopes; D044282:Receptor, Serotonin, 5-HT1A; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D003189:p-Methoxy-N-methylphenethylamine; D010739:Phospholipase D; D019206:GTP-Binding Protein alpha Subunits, Gi-Go