Protein kinase Cα participates in activation of store-operated Ca²⁺ channels in human glomerular mesangial cells

Protein kinase C (PKC) plays an important role in activat ing store-operated Ca²⁺ channels (SOC) in human mesan gial cells (MC). The present study was performed to determine the specific isoform(s) of conventional PKC involved in activating SOC in MC. Fura 2 fluorescence ratiometry showed that the thapsigargin- induced Ca²⁺ entry (equivalent to SOC) was significantly inhibited by 1 μM Gö-6976 (a specific PKCα and βI inhibitor) and PKCα antisense treatment (2.5 nM for 24-48 h). However, LY-379196 (PKCβ inhibitor) and 2,2',3,3',4,4'-hexahydroxy-l,l'-bi-phenyl-6,6'-dimethanoldimethyl ether (HBDDE; PKCα and γinhibitor) failed to affect thapsigargin-evoked activation of SOC. Single-channel analysis in the cell-attached configuration revealed that Gö-6976 and PKCα antisense significantly depressed thapsigargin-induced activation of SOC. However, LY-379196 and HBDDE did not affect the SOC responses. In inside-out patches, application of purified PKCα or βI, but not βII or γsignificantly rescued SOC from postexcision rundown. Western blot analysis revealed that thapsigargin evoked a decrease in cytosolic expression with a corresponding increase in membrane expression of PKCΑ and Γ. However, the translocation from cytosol to membranes was not detected for PKCΒI or βII. These results suggest that PKCα participates in the intracellular signaling pathway for activating SOC upon release of intracellular stores of Ca²⁺.