Zeng J, Smith K E, Chong P L
Department of Biochemistry, Meharry Medical College, Nashville, Tennessee.
Biophys J. 1993 Oct;65(4):1404-14. doi: 10.1016/S0006-3495(93)81204-9.
6-Carboxyfluorescein was employed to examine the effect of alcohol-induced lipid interdigitation on proton permeability in L-alpha-dipalmitoylphosphatidylcholine (DPPC) large unilamellar vesicles. Proton permeability was measured by monitoring the decrease of 6-carboxyfluorescein fluorescence after a pH gradient from 3.5 (outside the vesicle) to 8.0 (inside the vesicle) was established. At 20 degrees C and below 1.2 M ethanol, the fluorescence decrease is best described by a single exponential function. Above 1.2 M ethanol, the intensity decrease is better described by a two-exponential decay law. Using the fitted rate constants and the vesicle radii determined from light-scattering measurements, the proton permeability coefficient, P, in DPPC vesicles was calculated as a function of ethanol concentration. At 20 degrees C, P increases monotonically with increasing ethanol content up to 1.0 M, followed by an abrupt increase at 1.2 M. The vesicle size also exhibits a sudden increase at around 1.2 M ethanol, which has been shown to result from vesicle aggregation rather than vesicle fusion. The abrupt increases in P and in vesicle size occur at the concentration region close to the critical ethanol concentration for the formation of the fully interdigitated gel state of DPPC. At 14 degrees C, the abrupt change in P shifts to 1.9-2.0 M ethanol, completely in accordance with the ethanol-temperature phase diagram of interdigitated DPPC. Effects of methanol and benzyl alcohol on lipid interdigitation have also been examined. At 20 degrees C, DPPC large unilamellar vesicles exhibit a dramatic change in P at 3 M methanol and at 40 mM benzyl alcohol. These concentrations come close to the critical methanol and benzyl alcohol concentrations for the formation of fully interdigitated DPPC structures determined previously by others. It can be concluded that proton permeability increases dramatically as DPPC is transformed from the noninterdigitated gel to the fully interdigitated gel state by high concentrations of alcohol. This marked increase in proton permeability can be attributed to the combined effect of the changes in membrane thickness and surface charge density, due to the ethanol-induced lipid interdigitation. The possible effects of the increased proton permeability caused by ingested ethanol on gastric mucosal membranes are discussed.
使用6-羧基荧光素研究酒精诱导的脂质交叉对L-α-二棕榈酰磷脂酰胆碱（DPPC）大单层囊泡质子渗透性的影响。通过监测在建立从3.5（囊泡外部）到8.0（囊泡内部）的pH梯度后6-羧基荧光素荧光的降低来测量质子渗透性。在20℃且乙醇浓度低于1.2M时，荧光降低最好用单指数函数描述。在乙醇浓度高于1.2M时，强度降低用双指数衰减定律描述更好。使用拟合的速率常数和通过光散射测量确定的囊泡半径，计算DPPC囊泡中的质子渗透系数P作为乙醇浓度的函数。在20℃时，P随乙醇含量增加单调增加直至1.0M，然后在1.2M时突然增加。囊泡大小在乙醇浓度约为1.2M时也突然增加，这已被证明是由囊泡聚集而非囊泡融合导致的。P和囊泡大小的突然增加发生在接近DPPC形成完全交叉凝胶态的临界乙醇浓度的浓度区域。在14℃时，P的突然变化转移到1.9 - 2.0M乙醇，完全符合交叉DPPC的乙醇 - 温度相图。还研究了甲醇和苯甲醇对脂质交叉的影响。在20℃时，DPPC大单层囊泡在3M甲醇和40mM苯甲醇时P出现显著变化。这些浓度接近先前其他人确定的形成完全交叉DPPC结构的临界甲醇和苯甲醇浓度。可以得出结论，随着DPPC通过高浓度酒精从非交叉凝胶态转变为完全交叉凝胶态，质子渗透性显著增加。这种质子渗透性的显著增加可归因于乙醇诱导的脂质交叉导致的膜厚度和表面电荷密度变化的综合作用。讨论了摄入乙醇引起的质子渗透性增加对胃黏膜的可能影响。
