Location and dynamics of alpha-tocopherol in model phospholipid membranes with different charges.

Studies were made on the position and dynamics of the OH-group of alpha-tocopherol in phospholipid membranes. There was no difference in the spin-lattice (T1) relaxation times at the 5a-position of alpha-tocopherol labeled with 13C- or C19F3-determined from the nuclear magnetic resonance (NMR) spectra of liposomes positively charged with stearylamine (SA) and negatively charged with dicetylphosphate (DCP). The zeta-potentials of egg yolk phosphatidylcholine (EYPC) liposomes with and without SA or DCP were not affected by incorporation of 20 mol% alpha-tocopherol, though incorporation of 10 mol% ascorbyl-palmitate decreased the zeta-potentials of EYPC and EYPC-SA liposomes. The P==O stretching band (1235 cm-1) of the phosphate group and C==O stretching band (1734 cm-1) of the acyl ester linkage in dimyristoylphosphatidylcholine (DMPC) liposomes, measured by Fourier transform-infrared (FT-IR) spectroscopy, were not changed by incorporation of alpha-tocopherol. These results suggest that no specific interaction occurred between the OH-group of alpha-tocopherol and the polar interfacial region of the bilayer. The dynamic quenching effects of n-(N-oxy-4,4'-dimethyloxazolidine-2-yl)stearic acids (n-NSs) on the intrinsic fluorescence of alpha-tocopherol were in the order 5-NS > 7-NS = 12-NS > 16-NS. Acrylamide, a water-soluble fluorescence quencher with a very low capacity to penetrate through phospholipid bilayers, had very low quenching efficiency. These results indicate that the bulk of the chromanol moiety of alpha-tocopherol is located in a position close to that occupied by the nitroxide group of 5-NS in the membranes and is poorly exposed at the membrane surface.(ABSTRACT TRUNCATED AT 250 WORDS)     

Erratum

Vesicular fragments of biomembranes either induced or present as vesicles inside cells, have diameters which fall into two geometric series. Cells with intact cytoskeletons can take up a range of sizes but at mitosis, the cytoskeleton disappears, the cells round up and the plasma membrane can be considered as a vesicle in a stable phase which according to the theory should fall within one of the two possible geometric series. Thus, the size of the mother cell at mitosis and hence of the daughter cells are determined by these geometric series. The diameters of lymphoid cells fall into series which are consistent with the theory.     

Behavioral and cardiac responses after intracerebroventricular corticotropin-releasing hormone (CRH) administration: role of adrenal cortical hormones.

Intracerebroventricularly (icv) administered corticotropin-releasing hormone (CRH) produces a dose-dependent increase in heart rate in association with behavioral activation. The present study was designed to investigate whether these CRH-induced responses are dependent on adrenal function. The effects of adrenalectomy (ADX) and subsequent corticosterone replacement were studied. Administration icv of 300 ng of CRH failed to produce behavioral activation and tachycardia in ADX rats. Corticosterone replacement restored the CRH-induced behavioral response to preoperative levels, whereas the CRH-induced tachycardia was partially restored. This latter result may be related to the fact that the baseline heart rate of ADX animals appeared to be significantly higher than that of corticosterone-treated ADX animals. It is concluded that circulating adrenal corticosterone in ADX rats is involved in the expression of the behavioral and cardiac effect of central CRH.