title: Ionomycin causes susceptibility to phospholipase A2 while temperature-induced increases in membrane fluidity fail: possible involvement of actin fragmentation.
abstract: A diminution in the order of membrane lipids, which occurs during apoptosis, has been shown to correlate with increased membrane susceptibility to hydrolysis by secretory phospholipase A2. Studies with artificial membranes, however, have demonstrated that the relationship between membrane order and hydrolysis is more complex than suggested thus far by cell studies. To better resolve this relationship, this study focused on comparisons between increasing temperature and calcium ionophore as means of decreasing membrane order in S49 cells. Although these two treatments caused comparable changes in apparent membrane order as detected by steady-state fluorescence measurements, only ionophore treatment enhanced phospholipase activity. Experiments with exogenously-added phosphatidylserine indicated that the difference was not due to the presence of that anionic phospholipid in the outer membrane leaflet. Instead, analysis of the equilibration kinetics of various cationic membrane probes revealed that the difference could relate to the spacing of membrane lipids. Specifically, ionophore treatment increased that spacing while temperature only affected overall membrane order and fluidity. To consider the possibility that the distinction with ionophore might relate to the actin cytoskeleton, cells were stained with phalloidin and imaged via confocal microscopy. Ionophore caused disruption of actin fibers while increased temperature did not. This apparent connection between membrane hydrolysis and the cytoskeleton was further corroborated by examining the relationship among these events during apoptosis stimulated by thapsigargin.
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, UT 84602, USA. Electronic address: liz.gibbons7@gmail.com.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Gibbons
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, UT 84602, USA. Electronic address: cougarmurri@gmail.com.
authors.forename: Michael
authors.initials: M
authors.lastname: Murri
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, UT 84602, USA. Electronic address: amynicole7@gmail.com.
authors.forename: Amy
authors.initials: A
authors.lastname: Grabner
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, UT 84602, USA. Electronic address: ericfmoss@gmail.com.
authors.forename: Eric
authors.initials: E
authors.lastname: Moss
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, UT 84602, USA. Electronic address: laurylcampbell@gmail.com.
authors.forename: Lauryl
authors.initials: L
authors.lastname: Campbell
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, UT 84602, USA. Electronic address: jennelson5@gmail.com.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Nelson
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, UT 84602, USA. Electronic address: allan_judd@byu.edu.
authors.forename: Allan M
authors.initials: AM
authors.lastname: Judd
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, UT 84602, USA. Electronic address: john_bell@byu.edu.
authors.forename: John D
authors.initials: JD
authors.lastname: Bell
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000818:Animals; D061207:Calcium Ionophores / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000201:enzymology*; D006358:Hot Temperature; D015759:Ionomycin / Q000494:pharmacology*; D008560:Membrane Fluidity / Q000187:drug effects*; D051379:Mice; D010590:Phalloidine / Q000494:pharmacology; D054497:Phospholipases A2, Secretory / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism; D011042:Poisons / Q000494:pharmacology
chemical_list: D061207:Calcium Ionophores; D010743:Phospholipids; D011042:Poisons; D010590:Phalloidine; D015759:Ionomycin; D054497:Phospholipases A2, Secretory
keywords: Cytoskeleton; Membrane order; Merocyanine 540; Patman; Phalloidin; TMA-DPH