Recept Channels 2000 Jan 01;71:25-40.

Extracellular Ca2+ sensitivity of mGluR1alpha associated with persistent glutamate response in transfected CHO cells.

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We previously reported that the metabotropic glutamate receptor 1alpha (mGluR1alpha) can be activated not only by glutamate but also by extracellular Ca2+ (Ca2+o), and that Ser 166 in the extracellular domain determines the sensitivity to Ca2+o. In the present study, we investigated by intracellular Ca2+ (Ca2+i) imaging, the effect of Ca2+o on the glutamate responses of Chinese Hamster Ovary (CHO) cells stably expressing mGluR1alpha wild-type (CHO-wt). As a negative control, we carried out similar experiments using CHO cells expressing Ser166Asp mutant of mGluR1alpha (CHO-S166D) or the substance P receptor (CHO-SPR), which were not activated by Ca2+o application. We observed a remarkable prolongation of the duration of the glutamate response in CHO-wt cells in a Ca2+o concentration dependent manner. In CHO-S166D cells and CHO-SPR cells, only a small sustained component of the glutamate response was observed in the presence of Ca2+o. These sustained components were blocked by SKF-96365, a blocker of receptor-operated Ca2+-influx. Thus, it was concluded that the Ca2+o-sensing function of mGluR1alpha-wt induced the persistent opening of the receptor-operated Ca2+-permeable channels, probably by persistent activation of the receptor by glutamate. We additionally observed that the dose-response relationship of CHO-S166D and CHO-SPR shifted significantly by changing Ca2+o concentration, i.e. Ca2+o was required to maintain the normal ligand responses of these receptors.

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Species referenced: Xenopus
Genes referenced: spr