Kinetic limitation for the surface organization, dipole potential and topography of C10-CER

GABRIELA MARZARI; LAURA FANANI; BRUNO MAGGIO

Santiago del Estero

Congreso; XLIV Reunión Anual de la Sociedad Argentina de Biofísica; 2015

Sociedad Argentina de Biofísica

Ceramide, a mediator for cell-signaling, is a sphingolipid consisting of a sphingosine base N-linked to fatty acyl chains of different lengths. We studied the dependence on the compression-expansion kinetics of the interfacial organization and topography of films of ceramide N-acylated with a 10 carbon fatty acid (C10:0 Cer) in Lagmuir monolayers. At 21 °C, the compression isotherm of C10:0 Cer is liquid expanded between 90 to 60 Å2.molecule-1 with the expanded-condensed transition region at 23 mN.m-1. [1] The compression at different rates indicates that the film molecular packing, compressibility, dipole potential, morphology and optical thickness are kinetically limited. At 21 °C the "equilibrium spreading pressure" of C10:0 Cer is lower than 0.5 mN/m. Thus, at the usual compression rates, the ceramide film is in overcompressed state at all surface pressures. Similar to the compression process, the parameters measured during the expansion reveal that the interfacial organization also depends on the rate. After compression, the compressibility modulus remains with increased values that do not change with the expansion rate, indicating that the film remained more elastic. The isotherms showed different compressions-expansion hysteresis depending on the compression-expansion rate. The thermodynamic of hysteresis point to entropic-enthalpic compensations resulting mostly from favorable enthalpic contributions, from a more condensed packing, that overcome the unfavorable diminution of configurational entropy. The hysteresis indicates that part of the free energy of compression is stored in a kinetically limited interfacial organization (at the packing, electrostatic, rheologic and topographic levels) showing considerable inertia to return to the initial state. This reflects the retention of time-dependent molecular information at the ceramide interface under variations of surface pressure that might be important for its role as a lipid messenger.