Kano K, Fendler J H
Biochim Biophys Acta. 1978 May 18;509(2):289-99. doi: 10.1016/0005-2736(78)90048-2.
Pyranine is shown to be a convenient and sensitive probe for reporting pH values, pHi, at the interior of anionic and at the outer surface of cationic liposomes. It is well shielded from the phospholipid headgroups by water molecules in the interior of anionic liposomes, but it is bound to the surface of cationic liposomes. Hydrogen ion concentrations outside the liposomes, 'bulk pH values', pHo, were measured by a combination electrode. While pHi = pHo for neutral, pHi less than pHo for anionic and pHi greater than pHo for cationic liposomes prepared in 5.0 . 10(-3) M phosphate buffers. pKa values for the ionization of pyranine were 7.22 +/- 0.04 and 6.00 +/- 0.05 in water and at the external surface of cationic liposomes. The surface potential for cationic liposomes containing dipalmitoyl-DL-alpha-phosphatidylcholine, cholesterol and octadecylamine in the molar ratio of 1.00 : 0.634 : 1.01, were calcuated to be +72.2 mV. Proton permeabilities were measured for single and multicompartment anionic liposomes. Transfer of anionic liposomes prepared at a given pH to a solution of different pH resulted in a pH gradient if sodium phosphate or borate were used as buffers. In the presence of sodium acetate proton equilibration is promptly established.
吡喃荧光素被证明是一种方便且灵敏的探针，可用于报告阴离子脂质体内部和阳离子脂质体外表面的pH值（细胞内pH值，pHi）。在阴离子脂质体内部，水分子将其与磷脂头部基团很好地隔开，但它会结合在阳离子脂质体的表面。脂质体外部的氢离子浓度（“总体pH值”，pHo）通过复合电极进行测量。在5.0×10⁻³ M磷酸盐缓冲液中制备的中性脂质体，pHi = pHo；阴离子脂质体，pHi小于pHo；阳离子脂质体，pHi大于pHo。吡喃荧光素在水中和阳离子脂质体外表面的电离pKa值分别为7.22±0.04和6.00±0.05。对于摩尔比为1.00 : 0.634 : 1.01的含有二棕榈酰-DL-α-磷脂酰胆碱、胆固醇和十八胺的阳离子脂质体，计算得到其表面电位为+72.2 mV。对单室和多室阴离子脂质体的质子渗透性进行了测量。如果使用磷酸钠或硼酸盐作为缓冲剂，将在给定pH下制备的阴离子脂质体转移到不同pH的溶液中会产生pH梯度。在乙酸钠存在的情况下，质子能迅速达到平衡。
