Phosphorylation of lactate dehydrogenase by purified plasma membranes of loach liver cells: stimulation with insulin

It is established that insulin enhances the ability of the loach liver plasma membranes to phosphorylate lactate dehydrogenase. In the case of insulin-treated plasma membranes the amount of incorporated 32P is more than 4 times higher than that of the basal level. It is concluded that insulin-stimulated plasma membrane-dependent phosphorylation of the enzyme is one of the possible molecular mechanisms of hormone action on intracellular metabolism.     

Coupling between transmembrane calcium transport and membrane potential in retinal rod discs

Changes in the transmembrane potential of bovine rod discs were studied by use of the potential-sensitive fluorescence probes diS-C3-(5) and diBA-C4-(5). The disc membrane was shown to be impermeable to potassium ions. Their concentration in the disc is as high as 2.1 +/- 0.3 mM. The permeability of the disc membrane to Ca2+ was shown to be selective. The accumulation and release of Ca2+ were found to be accompanied by the generation of inside positive and inside negative transmembrane potentials, respectively. The uptake of Ca2+ in the discs may operate against the concentration gradient of the ion. The value of the potential developed is directly proportional to the logarithm of free Ca2+ concentration in the medium (delta phi m = 11.2 +/- 1.6 mV at 4.85 microM Ca2+fr). The accumulation of Ca2+ is decreased by sodium ions and totally inhibited by monensin. This indicates that a Na-Ca exchange process participates in Ca2+ uptake of photoreceptor discs.     

Prostaglandin I2 is less relaxant than prostaglandin E2 on the lamb ductus arteriosus.

Prostaglandin (PG) I2 and its stable metabolite, 6-keto-PGF1alpha, were tested on the isolated ductus arteriosus from mature fetal lambs. PGI2 relaxed the ductus in high doses (threshold 10(-6)M) and its activity disappeared on standing at room temperature for 30 minutes. 6-keto-PGF1alpha was inactive at all doses. By contrast, PGE2 produced a dose-dependent relaxation over a range between 10(-10) and 10(-6)M. These findings confirm that PGE2 is the most potent ductal relaxant among the known derivatives of arachidonic acid. PGE2 probably maintains ductus patency in the fetus and, together with PGE1, remains the compound of choice in the management of newborns requiring a viable ductus for survival.     

Overnight dexamethasone suppression test: normal responses and the diagnosis of Cushing's syndrome

Serum cortisol levels were measured the morning after the administration of 1 mg of dexamethasone. Only 5 of 190 subjects had serum cortisol levels greater than 2 micrograms/dL. Thus, the normal value after dexamethasone suppression is less than 2 micrograms/dL rather than less than 5 micrograms/dL as has generally been accepted. The distinction is important because some individuals with Cushing's syndrome partially suppress their cortisol levels to less than 5 but more than 2 micrograms/dL during the test procedure. Thus, the use of 5 micrograms/dL as the normal value may lead to an unnecessary delay in diagnosis.     

Dominant lethal studies in male mice after exposure to 2.45 GHz microwave radiation

Adult male mice had the lower halves of their bodies exposed in a waveguide system to 2.45 GHz microwave radiation for 30 min. The half body dose-rate of 43 W kg-1 had been shown in a previous study [7] to deplete severely the heat-sensitive stages of sperm production. The males were mated at intervals to adult hybrid females over the following 8-10 weeks. There was no significant reduction in post-implantation survival, suggesting that the microwave exposure did not have a mutagenic effect on the male germ cells. However, pregnancy rate was significantly reduced in weeks 3, 4, 5 and 6; reaching a minimum of about 10% of the control value in weeks 4 and 5. The occurrence of low values in weeks 4 and 5 correlated well with the expected reductions in sperm count due to the pattern of depletion of the spermatogenic epithelium of the testes. Thus it was concluded that the reduced pregnancy rate resulted from reduced male fertility. Pre-implantation survival can also be affected by reduced sperm count [8] and was significantly reduced in this study but it correlated less well with the anticipated heat response. A further study is in progress looking at the contribution of sperm count and sperm abnormality to the results.     

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)