Cloning, Distribution and Functional Expression of the Human mGlu 6 Metabotropic Glutamate Receptor

Abstract

The cDNA encoding the human metabotropic glutamate receptor type 6 (hmGlu 6) was isolated from a human retinal cDNA library. The deduced primary sequence (877 amino acids) of the hmGlu 6 receptor was 93.5% identical to its rat counterpart and shared 69.8% sequence identity with the related hmGlu 4 receptor clone (912 amino acids), isolated in parallel from a human brain cDNA library. In situ hybridization revealed that the hmGlu 6 mRNA is highly expressed in cells located in the inner nuclear layer of the human retina, presumably bipolar neurons. Neither PCR analysis nor in situ hybridization could detect hmGlu 6 mRNA in human brain. When stably expressed in Chinese hamster ovary cells (CHO-K1) the hmGlu 6 receptor inhibited adenylate cyclase through a pertussis toxin-sensitive G-protein, and reduced forskolin-elevated cyclic adenosine monophosphate (cAMP) levels in response to agonists. The rank order of agonist potency was l(+)-2-amino-4-phosphonobutyric acid ( l-AP4) > l-serine-O-phosphate > l-glutamate > quisqualate = (1 S,3 R)-1-aminocyclopentane-1,3-dicarboxylic acid ((1 S,3 R)-ACPD). (2 S,3 S,4 S)-α-(carboxycyclopropyl)-glycine ( l-CCG-1) was a partial agonist at the hmGlu 6 receptor, with a potency approaching that of l-serine- O-phosphate. © 1997 Published by Elsevier Science Ltd. All rights reserved.