EFFECTS OF PRESSURE AND LOCAL-ANESTHETIC TETRACAINE ON DIPALMITOYLPHOSPHATIDYLCHOLINE BILAYERS

The temperature-pressure phase diagram of dipalmitoylphosphatidylcholi ne (DPPC) multilamellar vesicles was constructed in the presence of a local anesthetic tetracaine hydrochloride (TC-HCl). The phase-transiti on temperatures under various pressures were determined by the method of high-pressure light transmission. The temperature of the main trans ition from the ripple gel (P-beta') to the liquid crystal (L-alpha) ph ase was depressed by the addition of TC-HCl and elevated by applicatio n 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 interdi gitated gel (LbetaI) phase has been observed under high pressure above 100 MPa in the absence of TC-HCl. The LbetaI phase is known to be ind uced also by a variety of small amphiphilic molecules such as ethanol, benzyl alcohol and TC-HCl. In the presence of TC-HCl ranging in conce ntration up to 20.0 mmol kg(-1), the LbetaI phase instead of the P-bet a' phase appeared at higher pressure. Present results revealed that pr essure facilitates, rather than antagonizes, the effect of TC-HCl on t he occurrence of interdigitated gel phase. Furthermore, two regions of two phase coexistence were observed under high pressure in the presen ce of TC-HCl. One is probably a region of coexisting L beta I and L-al pha phase, which was found between LbetaI and L-alpha phases under var ious pressures. The other is probably a region of coexisting L-beta' a nd LbetaI 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 bel ow ca. 35 degrees C.