Effects of pressure and local anesthetic tetracaine on dipalmitoylphosphatidylcholine bilayers.

The temperature-pressure phase diagram of dipalmitoylphosphatidylcholine (DPPC) multilamellar vesicles was constructed in the presence of a local anesthetic tetracaine hydrochloride (TC-HCl). The phase-transition temperatures under various pressures were determined by the method of high-pressure light transmission. The temperature of the main transition from the ripple gel (P'(beta)) to the liquid crystal (L(alpha)) phase was depressed by the addition of TC-HCl and elevated by application of pressure up to 150 MPa. The temperature of the pretransition from the lamellar gel (L'(beta)) to the P'(beta) phase was also depressed by the addition of TC-HCl below ca. 10.0 mmol kg(-1) and elevated by the pressure below ca. 50 MPa. Therefore, pressure-anesthetic antagonism for both phase-transitions was confirmed. The pressure-induced interdigitated gel (L(beta)I) phase has been observed under high pressure above 100 MPa in the absence of TC-HCl. The L(beta)I phase is known to be induced also by a variety of small amphiphilic molecules such as ethanol, benzyl alcohol and TC-HCl. In the presence of TC-HCl ranging in concentration up to 20.0 mmol kg(-1), the L(beta)I phase instead of the P'(beta) phase appeared at higher pressure. Present results revealed that pressure facilitates, rather than antagonizes, the effect of TC-HCl on the occurrence of interdigitated gel phase. Furthermore, two regions of two phase coexistence were observed under high pressure in the presence of TC-HCl. One is probably a region of coexisting L(beta)I and L(alpha) phase, which was found between L(beta)I and L(alpha) phases under various pressures. The other is probably a region of coexisting L'(beta) and L(beta)I phase, which was observed in the presence of TC-HCl up to 10.0 mmol kg(-1) at the pressure above 40 MPa and at the temperature below ca. 35 degrees C.