The common inhalational anesthetic isoflurane induces apoptosis via activation of inositol 1,4,5-trisphosphate receptors

Background: lsoflurane induces cell apoptosis by an unknown mechanism. The authors hypothesized that isoflurane activates inositol 1,4,5 -trisphosphate (IP3) receptors on the endoplasmic reticulum (ER) membrane, causing excessive calcium release, triggering apoptosis. Methods: The authors determined isoflurane-induced cytotoxicity by measuring caspase-3 activity, lactate dehydrogenase release, MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3carboxymethoxy-phenyl)-2-(4-sulfophenyl)-2H-tetrazoliuin, inner salt) reduction, and imaging analysis of cell damage markers (annexin V and propidium iodide staining) in different cell types. The authors used the chicken B lymphocyte with a total knock-out of IP3 receptors, PC12 cells with elevated IP3 receptor activity (transfected with L286V presenilin 1), striatal cells with a knock-in of Q111 Huntingtin, and each cell tine's corresponding wild-type controls. The authors also measured the isoflurane-evoked changes of calcium concentration in cytosol and/or mitochondria in these cells. Results: Isoflurane induced apoptosis concentration- and time-dependently, and sequentially elevated cytosolic and then mitochondrial calcium in the chicken B-lymphocyte wild-type but not the IP3 receptor total knock-out cells. Thapsigargin, a calcium adenosine triphosphatase inhibitor on ER membranes, induced apoptosis and elevations of calcium in cytosol and mitochondria in both chicken B-lymphocyte wildtype and IP3 receptor total knock-out cells. isoflurane induced significantly more neurotoxicity and greater calcium release from the ER in L286V PC12 and Q111 Huntingtin striatal cells than in their corresponding wild-type controls, both of which were significantly inhibited by the IP3 receptor antagonist xestospongin C.