Noradrenaline release-inhibiting receptors on PC12 cells devoid of alpha(2(-)) and CB(1) receptors: similarities to presynaptic imidazoline and edg receptors.

The aim of the present study was to classify release-inhibiting receptors on rat pheochromocytoma PC12 cells. Veratridine-evoked [3H]noradrenaline release from PC12 cells was inhibited by micromolar concentrations of the imidazoline and guanidine derivatives cirazoline, clonidine, aganodine, 1,3-di(2-tolyl)guanidine, BDF6143 and agmatine, and of the cannabinoid receptor agonist WIN55,212-2 (R(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolo-[1,2,3-de]-1,4-benzoxazin-yl](1-naphthalenyl)methanone mesylate), but not by noradrenaline. The inhibitory effect of clonidine was antagonized by micromolar concentrations of rauwolscine and SR141716A (N-[piperidin-1-yl]-5-[4-chlorophenyl]-1-[2,4-dichlorophenyl]-4-methyl-1H-pyrazole-3-carboxamide). The potencies of the agonists and antagonists were compatible with an action at previously characterized presynaptic imidazoline receptors. 1-Oleoyl-lysophosphatidic acid, but not sphingosine-1-phosphate, produced an inhibition of release that was antagonized by 30 microM rauwolscine, 1 microM SR141716A and 10 microM LY320135 as well as by pretreatment of the cells with 100 microM clonidine for 72 h. Polymerase chain reaction (PCR) experiments on cDNA from PC12 mRNA suggest mRNA expression of lysophospholipid receptors encoded by the genes edg2, edg3, edg5 and edg7, but not of receptors encoded by edg1, edg4, edg6 and edg8, and not of alpha(2A(-))nd CB(1) receptors. In conclusion, PC12 cells are not endowed with alpha(2)-adrenoceptors and CB(1) cannabinoid receptors, but with an inhibitory receptor recognizing imidazolines, guanidines and WIN55,212-2 similar to that on sympathetic nerves. The PCR results and the ability of 1-oleoyl-LPA to mimic these drugs (also with respect to their susceptibility to antagonists) suggest that the release-inhibiting receptor may be an edg-encoded lysophospholipid receptor.