Figure 3. Bupivacaine uptake into liposomes exhibiting a pH gradient. Uptake of local anesthetic into 1,2-dioleoyl-sn-glycero-3-phosphocholine:Cholesterol large unilamellar vesicles (5 mM phospholipid) was determined at three bupivacaine concentrations: 1 mM (closed circle); 2 mM (closed square); and 3 mM (closed triangle). In addition, association of bupivacaine (3 mM) with control liposomes (no pH gradient) was determined (closed inverted triangle).