title: Relationships between membrane water molecules and Patman equilibration kinetics at temperatures far above the phosphatidylcholine melting point.
abstract: The naphthalene-based fluorescent probes Patman and Laurdan detect bilayer polarity at the level of the phospholipid glycerol backbone. This polarity increases with temperature in the liquid-crystalline phase of phosphatidylcholines and was observed even 90°C above the melting temperature. This study explores mechanisms associated with this phenomenon. Measurements of probe anisotropy and experiments conducted at 1M NaCl or KCl (to reduce water permittivity) revealed that this effect represents interactions of water molecules with the probes without proportional increases in probe mobility. Furthermore, comparison of emission spectra to Monte Carlo simulations indicated that the increased polarity represents elevation in probe access to water molecules rather than increased mobility of relevant bilayer waters. Equilibration of these probes with the membrane involves at least two steps which were distinguished by the membrane microenvironment reported by the probe. The difference in those microenvironments also changed with temperature in the liquid-crystalline phase in that the equilibrium state was less polar than the initial environment detected by Patman at temperatures near the melting point, more polar at higher temperatures, and again less polar as temperature was raised further. Laurdan also displayed this level of complexity during equilibration, although the relationship to temperature differed quantitatively from that experienced by Patman. This kinetic approach provides a novel way to study in molecular detail basic principles of what happens to the membrane environment around an individual amphipathic molecule as it penetrates the bilayer. Moreover, it provides evidence of unexpected and interesting membrane behaviors far from the phase transition.
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah 84602, USA.
authors.forename: Alexandra R
authors.initials: AR
authors.lastname: Vaughn
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah 84602, USA.
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Bell
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah 84602, USA.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Gibbons
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah 84602, USA.
authors.forename: Caitlin
authors.initials: C
authors.lastname: Askew
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah 84602, USA.
authors.forename: Hannabeth
authors.initials: H
authors.lastname: Franchino
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah 84602, USA.
authors.forename: Kelsey
authors.initials: K
authors.lastname: Hirsche
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah 84602, USA.
authors.forename: Linea
authors.initials: L
authors.lastname: Kemsley
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah 84602, USA.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Melchor
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah 84602, USA.
authors.forename: Emma
authors.initials: E
authors.lastname: Moulton
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah 84602, USA.
authors.forename: Morgan
authors.initials: M
authors.lastname: Schwab
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah 84602, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Nelson
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah 84602, USA. Electronic address: john_bell@byu.edu.
authors.forename: John D
authors.initials: JD
authors.lastname: Bell
mesh_terms: D015081:2-Naphthylamine / Q000031:analogs & derivatives* / Q000737:chemistry; D000465:Algorithms; D016880:Anisotropy; D002462:Cell Membrane / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry; D007700:Kinetics; D007848:Laurates / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D009010:Monte Carlo Method; D010169:Palmitic Acids / Q000737:chemistry*; D044367:Phase Transition; D010713:Phosphatidylcholines / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D005456:Fluorescent Dyes; D007848:Laurates; D008051:Lipid Bilayers; D010169:Palmitic Acids; D010713:Phosphatidylcholines; C103351:patman; D014867:Water; D015081:2-Naphthylamine; C065580:laurdan
keywords: Fluorescence; Kinetics; Laurdan; Liquid–Crystalline; Membrane water; Patman