The effects of inositol 1,4,5-trisphosphate, prepared from human erythrocyte ghosts, on Ca 2+ release from intracellular store sites were studied in saponin-treated guinea pig peritoneal macrophages. Micromolar concentrations of inositol 1,4,5-trisphosphate released Ca 2+ within 1 min from store sites which had accumulated Ca 2+ in the presence of 10 mM-NaN 3 . In the presence of 10 mM-NaN 3 , the Ca 2+ accumulated in the presence of oxalate was seen in the endoplasmic reticulum of saponin-treated macrophages by electron microscopy, indicating that the site of Ca 2+ released by inositol 1,4,5-trisphophate may be endoplasmic reticulum-like membranes. When the concentrations of free Ca 2+ were over 3.5x10 -6 M, the release of Ca 2+ by this agent was inhibited. This inhibition may be due to either the higher concentration of extra-vesicular free Ca 2+ or the larger accumulation of Ca 2+ into the store site or perhaps both effects. MgCl 2 also had an inhibitory effect on the Ca 2+ release. Inositol 1,4,5-trisphosphate also released Ca 2+ from cardiac sarcoplasmic reticulum, but not from erythrocyte inside-out vesicles.
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Cell Biology