Phospholipase C-b (PLC-b) hydrolyses phosphatidylinositol 4,5-bisphosphate and generates inositol 1,4,5-trisphosphate in response to activation of various G protein-coupled receptors (GPCRs). Using glial cells from knock-out mice lacking either PLC-b1 [PLC-b1 (-/-)] or PLC-b3 [PLC-b3 (-/-)], we examined which isotype of PLC-b participated in the cellular signaling events triggered by thrombin. Generation of inositol phosphates (IPs) was enhanced by thrombin in PLC-b1 (-/-) cells, but was negligible in PLC-b3 (-/-) cells. Expression of PLC-b3 in PLC-b3 (-/-) cells resulted in an increase in pertussis toxin (PTx)-sensitive IPs in response to thrombin as well as to PAR1-specific peptide, while expression of PLC-b1 in PLC-b1 (-/-) cells did not have any effect on IP generation. The thrombin-induced [Ca2+]i increase was delayed and attenuated in PLC-b3 (-/-) cells, but normal in PLC-b1 (-/-) cells. Pertussis toxin evoked a delayed [Ca2+]i increase in PLC-b3 (-/-) cells as well as in PLC-b1 (-/-) cells. These results suggest that activation of PLC-b3 by pertussis toxin-sensitive G proteins is responsible for the transient [Ca2+]i increase in response to thrombin, whereas the delayed [Ca2+]i increase may be due to activation of some other PLC, such as PLC-b4, acting via PTx-insensitive G proteins.

Keywords: Calcium, Glial Cells Inositol Phosphates, GPCR, PLC-b3