Observation of the main phase transition of dinervonoylphosphocholine giant liposomes by fluorescence microscopy.
The phase heterogeneity of giant unilamellar dinervonoylphosphocholine (DNPC) vesicles in the course of the main phase transition was investigated by confocal fluorescence microscopy observing the fluorescence from the membrane incorporated lipid analog, 1-palmitoyl-2-(N-4-nitrobenz-2-oxa-1,3-diazol)aminocaproyl-sn-glycero-3-phosphocholine (NBDPC). These data were supplemented by differential scanning calorimetry (DSC) of DNPC large unilamellar vesicles (LUV, diameter approximately 0.1 and 0.2 microm) and multilamellar vesicles (MLV). The present data collected upon cooling reveal a lack of micron-scale gel and fluid phase coexistence in DNPC GUVs above the temperature of 20.5 degrees C, this temperature corresponding closely to the heat capacity maxima (T(em)) of DNPC MLVs and LUVs (T(em) approximately 21 degrees C), measured upon DSC cooling scans. This is in keeping with the model for phospholipid main transition inferred from our previous fluorescence spectroscopy data for DMPC, DPPC, and DNPC LUVs. More specifically, the current experiments provide further support for the phospholipid main transition involving a first-order process, with the characteristic two-phase coexistence converting into an intermediate phase in the proximity of T(em). This at least macroscopically homogenous intermediate phase would then transform into the liquid crystalline state by a second-order process, with further increase in acyl chain trans-->gauche isomerization.
Helsinki Biophysics and Biomembrane Group, Institute of Biomedicine, University of Helsinki, Finland.
Antti J
AJ
Metso
Hongxia
H
Zhao
Ilkka
I
Tuunainen
Paavo K J
PK
Kinnunen
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000031:analogs & derivatives* / Q000737:chemistry; D055592:Biophysical Phenomena; D001703:Biophysics; D002152:Calorimetry, Differential Scanning; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D006358:Hot Temperature; D008051:Lipid Bilayers; D008081:Liposomes / Q000737:chemistry*; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence / Q000379:methods*; D010713:Phosphatidylcholines / Q000737:chemistry; D010767:Phosphorylcholine / Q000031:analogs & derivatives* / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013237:Stereoisomerism; D013696:Temperature
D008051:Lipid Bilayers; D008081:Liposomes; D010713:Phosphatidylcholines; C503355:palmitoyl-2-(N-4-nitrobenz-2-oxa-1,3-diazol)aminocaproyl-sn-glycero-3-phosphocholine; D010767:Phosphorylcholine; D015060:1,2-Dipalmitoylphosphatidylcholine; D004134:Dimyristoylphosphatidylcholine