Changes in surface capacitance and conductance parallel to phospholipid membranes associated with phase transition: effects of halothane.
The effects of phase transition on the surface capacitance and conductance parallel to dipalmitoyl- (DPPC) and dimyristoyl-phosphatidylcholine (DMPC) membranes were studied by impedance dispersion. The phospholipid aggregates were embedded into pores of a polycarbonate filter and the impedance dispersions were measured at a frequency range from 30 Hz to 1.0 MHz. When the frequency was below 120 kHz, the capacitance showed a peak at the pretransition temperature and a steep rise at the main-transition temperature. In this system, the observed capacitance consists of frequency-dependent and -independent parts. The frequency-dependent part is a surface phenomenon and arises from the lateral motion of counterions at the membrane/water interface. The frequency-independent part represents mainly the properties of the bulk lipid phase. Addition of halothane decreased the total capacitance of the DPPC aggregates at the low frequency range to 1/2 to 1/8 of the control depending upon the temperature. The surface component was solely responsible for this capacitance decrease, because the non-surface component was slightly increased instead. The data suggest that halothane inhibited the lateral ionic flow parallel to the interface.
Yoshida
T
T
Department of Applied Chemistry, Nagoya Institute of Technology, Japan.
Taga
K
K
Okabayashi
H
H
Kamaya
H
H
Ueda
I
I
D015060:1,2-Dipalmitoylphosphatidylcholine; D004134:Dimyristoylphosphatidylcholine; D004553:Electric Conductivity; D006221:Halothane; D008081:Liposomes; D008433:Mathematics; D008962:Models, Theoretical; D008968:Molecular Conformation; D013499:Surface Properties; D013816:Thermodynamics
D008081:Liposomes; D015060:1,2-Dipalmitoylphosphatidylcholine; D004134:Dimyristoylphosphatidylcholine; D006221:Halothane