title: Increase in Ca2+ permeability of intracellular Ca2+ store membrane of saponin-treated guinea pig peritoneal macrophages by inositol 1,4,5-trisphosphate.
abstract: Inositol 1,4,5-trisphosphate (InsP3) releases Ca2+ from the non-mitochondrial Ca2+ store site of various types of cells. To study the mechanisms of the Ca2+ release from the store site, the effect of InsP3 on the passive Ca2+ release and influx, and the active Ca2+ uptake in the presence of oxalate, was examined using saponin-treated guinea pig peritoneal macrophages. InsP3 stimulated the passive Ca2+ release and influx. Although InsP3 slightly inhibited the active Ca2+ uptake in the presence of oxalate, it seems unlikely that the Ca2+ release by this agent is caused by the inhibition of the Ca2+ uptake, because the addition of apyrase or hexokinase (which removes ATP within 30 s, so that no more Ca2+ can be accumulated) or vanadate (which inhibits the Ca2+ uptake) resulted in very slow release of Ca2+. These results suggest that the Ca2+ permeability of the Ca2+ store membrane is increased by InsP3. InsP3 did not cause an increase in the Ca2+ permeability of phospholipid vesicles (liposomes), indicating that this agent may bring about Ca2+ release by a specific effect on the physiologically relevant Ca2+ channels or carriers in the non-mitochondrial Ca2+ store site. The passive Ca2+ release by InsP3 was enhanced by ATP and an unhydrolyzable ATP analogue, 5'-adenylyimidodiphosphate, but not by ADP or AMP. The passive Ca2+ release by InsP3 was observed even at 0 degree C.
mesh_terms: D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism; D006168:Guinea Pigs; D006801:Humans; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism*; D008081:Liposomes / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism*; D010529:Peritoneal Cavity; D010539:Permeability; D012503:Saponins / Q000494:pharmacology*; D013403:Sugar Phosphates / Q000494:pharmacology*; D014638:Vanadates; D014639:Vanadium / Q000494:pharmacology
chemical_list: D007295:Inositol Phosphates; D008081:Liposomes; D012503:Saponins; D013403:Sugar Phosphates; D014639:Vanadium; D014638:Vanadates; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D002118:Calcium