Phospholipase C-β3 mediates the thrombin-induced Ca²⁺ response in glial cells

Phospholipase C-β (PLC-β) 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-β1 [PLC-β1 (-/-)] or PLC-β3 [PLC-β3 (-/-)], we examined which isotype of PLC- participated in the cellular signaling events triggered by thrombin. Generation of inositol phosphates (IPs) was enhanced by thrombin in PLC-β1 (-/-) cells, but was negligible in PLC-β3 (-/-) cells. Expression of PLC-β in PLC-β(-/-) cells resulted in an increase in pertussis toxin (PTx)-sensitive IPs in response to thrombin as well as to PARI-specific peptide, while expression of PLC-β1 in PLC-β1 (-/-) cells did not have any effect on IP generation. The thrombin-induced [Ca²⁺]_i increase was delayed and attenuated in PLC-β3 (-/-) cells, but normal in PLC-β1 (-/-) cells. Pertussis toxin evoked a delayed [Ca²⁺], increase in PLC-β3 (-/-) cells as well as in PLC-β1 (-/-) cells. These results suggest that activation of PLC-β3 by pertussis toxin-sensitive G proteins is responsible for the transient [Ca²⁺], increase in response to thrombin, whereas the delayed [Ca²⁺], increase may be due to activation of some other PLC, such as PLC-β4, acting via PTx-insensitive G proteins.