The effects of temperature upon the electrophysiological properties of Tetrahymena pyriformis-NT1

Cells of Tetrahymena pyriformis--NT1 were cultured at 38 degrees C (Tg 38 degrees C) and 20 degrees C (Tg 20 degrees C) and their properties investigated over the range 0-40 degrees C. Tg 20 degrees C cells were viable in the range 3-33 degrees C and changes in their properties were readily reversible between 10 degrees C and 30 degrees C. Tg 38 degrees cells were viable in the range 40-10 degrees C and their property changes were immediately reversible in the range 40-23 degrees C. The I-V relations of Tg 38 degrees C cells showed increased excitability as the cells were cooled from 40 degrees C. At 10 degrees C there was a considerable loss of excitability and slope resistance. Cooling Tg 20 degrees C cells from 20 degrees C gave a similar pattern, although over a narrower temperature range. Warming Tg 20 degrees C Tetrahymena above 20 degrees C led to a progressive loss of excitability and the cells were markedly less viable above 35 degrees C. Within physiological limits the regenerative spike magnitude, repolarization time, time to peak and input resistance increased as temperature was lowered, whereas resting potential was diminished. When compared at their growth temperatures and most intermediate temperatures, the value of the various parameters monitored were generally different for the two cultures. The Q10 value for resting potential changes of Tg 20 degrees C cells about 20 degrees C was 1.20. As in T. vorax this was significantly (P less than 0.01) greater than that predicted for a diffusion potential and suggested that T. pyriformis--NT1 may have an electrogenic pump component in its membrane potential.     

Changes in lipid fluidity and fatty acid composition with altered culture temperature in Tetrahymena pyriformis-NT1

Cultures of T. pyriformis-NT1 were grown at 20 degrees C (Tg 20 degrees C) and 38 degrees C (Tg 38 degrees C). G.L.C. analysis and D.P.H. fluorescence polarization measurements in extracted phospholipids indicated that there was increased saturation of fatty acids and relatively reduced fluidity as growth temperature was increased. Breakpoints occurred in the Arrhenius plots of fluorescence polarization at 16 degrees C for Tg 38 degrees C total extracted phospholipids and 9 degrees C for Tg 20 degrees C lipids.     

Osmotic behaviour of Acholeplasma laidlawii B cells with membrane lipids in liquid-crystalline and gel state.

The osmotic behaviour of Acholeplasma laidlawii B cells was investigated with combined spectrophotometric and enzymatic measurements. The conclusion could be drawn that this osmotic behaviour depends largely on the physical state of the membrane lipids. When part of the membrane lipids is in the liquid-crystalline phase the cell is able to swell and behaves as a good osmometer. However, when the membrane lipid is in the gel phase, the cell is unable to swell and the change in absorbance of the cell suspension is then completely due to lysis.     

Temperature-dependent changes in circadian patterns of cricket premating behaviour

ABSTRACT. Male-calling and female-walking in Teleogryllus commodus (Walker) is mainly performed during the night (in LD 12:12 at constant temperature). Cold nights of 1–7°C switched both activities from night to daytime. After cold exposure it took several transient cycles until the original phase angle difference to lights-out was re-established. The involvement of a circadian clock in these processes was revealed by observing the free-running rhythm in constant light after a cold night. The rhythm was delayed, evidently due to the resetting of the biological clock by the cold exposure. This temporal alteration of premating behaviour in males and females is discussed in relation to intraspecific consequences, its adaptive value in natural conditions, and with respect to the potential parallel effects in parasites and predators.     

Physical state changes of membrane lipids in human lung adenocarcinoma A(549) cells and their resistance to cisplatin

The properties of membrane lipids in sensitive A(549) and resistant A(549)/DDP cells to cis-dichlorodiammine platinum[II] (cisplatin) were examined by combining different approaches. The results showed that fluorescence intensity (deltaF) of Merocyanine 540 (MC540) was 93.5 +/- 21.8 for the sensitive A(549) cells and 49.5 +/- 11.2 for the resistive A(549)/DDP cells, monitored by flow cytometry, which may indicate that membrane lipid packing of the sensitive A(549) cells were looser than that of the resistant A(549)/DDP cells. Diffusion rate of N-(7-nitro-2,1,3-benzoxadiazol-4-yl)-1,2-hexadecanoyl-Sn-glycero-3-phosphatidyl-ethanolamine (NBD-PE) was slower in A(549)/DDP cells than in A(549) cells as detected by fluorescence recovery after photobleaching (FRAP) technique. Fatty acid analysis of the membrane lipids showed 21.6, 27.0 and 31.8% increase in the amount of C(18:1), C(18:2) and C(18:3) fatty acid, respectively, in A(549) cells as compared to A(549)/DDP cells. The total amount of unsaturated fatty acids in the plasma membrane lipid is 69.13% +/- 2.2% for A(549), and 55.08% +/- 1.8% for A(549)/DDP cells, respectively. The resistance to cisplatin in A(549)/DDP cells was confirmed by the measurements of the transmembrane influx of Rhodamine-123, cisplatin or Bodipy-cisplatin by fluorescence assay and inductively coupled plasma mass spectrometry (ICP-MS). From the results described previously, it is concluded that changes in the membrane lipids "composition" cause a change in the physical state of the plasma membrane lipids and that this may be associated with the resistance of A(549)/DDP cells to cisplatin.     

Evidence for a correlation between swimming velocity and membrane fluidity of Tetrahymena cells

The influence of the physical state of the membrane on the swimming behaviour of Tetrahymena pyriformis was studied in cells with lipid-modified membranes. When the growth temperature of Tetrahymena cells was increased from 15 degrees C to 34 degrees C or decreased from 39 degrees C to 15 degrees C, their swimming velocity changed gradually in a similar to the adaptive change in membrane lipid composition. Therefore, such adaptive changes in swimming velocity were not observed during short exposures to a different environment. Tetrahymena cells adapted to 34 degrees C swam at 570 microns/s. On incubation at 15 degrees C these cells swam at 100 microns/s. When the temperature was increased to 34 degrees C after a 90-min incubation at 15 degrees C, the initial velocity was immediately recovered. On replacement of tetrahymanol with ergosterol, the swimming velocity of 34 degrees C-grown cells decreased to 210 microns/s, and the cells ceased to move when the temperature was decreased to 15 degrees C. To investigate the influence of the physical state of the membrane on the swimming velocity, total phospholipids were prepared from Tetrahymena cells grown under these different conditions. The fluidities of liposomes of these phospholipid were measured using stearate spin probe. The membrane fluidity of the cells cooled to 15 degrees C increased gradually during incubation at 15 degrees C. On the other hand, the fluidity of the heated cell decreased during incubation at 34 degrees C. Replacement of tetrahymanol with ergosterol decreased the membrane fluidity markedly. Consequently, a good correlation was observed between swimming velocity and membrane fluidity; as the membrane fluidity increased, the swimming velocity increased linearly up to 600 microns/s. These results provide evidence for the regulation of the swimming behaviour by physical properties of the membrane.     

Temperature-dependent changes in the profile of the sarcoplasmic reticulum membrane hydrophobic zones]

The dependence of the state of the hydrophobic zone of rabbit sarcoplasmic reticulum (SR) membranes on temperature of the membrane fragment suspension before rapid freezing was studied by the freeze fracturing technique. It was shown that within the temperature range of--15-- +37 degrees C the amount of intramembrane particles and their distribution in the membrane plane and between their convex and concave surfaces do not practically depend on the temperature of the SR membrane suspension. This is indicative of the lack of correlation between the physical state of the phospholipid matrix (gel -- liquid crystal) before freezing and the nature of the profile of the membrane hydrophobic zone revealed after fracturing. The disturbances in the protein -- lipid interactions in the membrane under the effects of mersalyl or aqueous solutions of diethyl ester followed by complete inactivation of Ca2+-dependent ATPase lead to a decrease in the amount of intramembrane particles, which is especially well-pronounced at 37 degrees and -15 degrees C.     

Rapid changes in soybean root membrane lipids with altered temperature

In soybean roots, as temperature was increased between 15° and 30°, palmitic and stearic acids increased, and oleic, linoleic, and linolenic acids decreased in both plasmalemma and mitochondrial membrane fractions. As temperature was decreased, the reverse trend occurred. Membranes in both the mitochondria and plasmalemma responded with a significant shift in fatty acid composition in 48 hr, often in 24 hr. Mitochondria responded more quickly than the plasmalemma, particularly at the lower temperature.     

Viscosity changes of erythrochyte membrane and membrane lipids at transition temperature

A non-linearity in the changes of viscosity with temperature was found in sonicated human erythrocyte membranes at 18–19 °C. At the same temperature, a break was observed in the viscosity of the extracted membrane lipids, the cholesterol content of which was varied by means of Sephadex LH 20 column chromatography. It is inferred that the break observed in the membranes corresponds to the transition temperature of the erythrocyte membrane lipids. The applied method of direct viscosimetry is relatively simple and cheap in comparison to the well known methods of ESR spectroscopy or differential scanning calorimetry, which have been hitherto widely used in determining thermal transition points in different systems.Viscosity measurements may be compared to light scattering or fluorescence measurements, introduced recently for the determination of phase transitions (Träuble, H. (1971) Naturwissenschaften 58, 277–284, and Lussan, C. and Faucon, J.F. (1971) FEBS Lett. 19, 186–188).     

Temperature-induced changes in the hydroxy and non-hydroxy fatty acid-containing sphingolipids abundant in the surface membrane of Tetrahymena pyriformis NT-1

Sphingolipids make up 30 to 40 mole % of the phospholipids found in the surface membrane of Tetrahymena pyriformis NT-1. We have identified the two major classes as non-hydroxy fatty acid-containing ceramide-2-aminoethylphosphonate (NCAEP) and alpha-hydroxy fatty acid-containing ceramide-2-aminoethylphosphonate (HCAEP). Both classes were well represented in cells grown at 39 degrees C. At this temperature their principal long chain bases were n-hexadeca-4-sphingenine and n-nonadeca-4-sphingenine. The major fatty acid of NCAEP from 39 degrees C-grown cells was palmitic acid and that of HCAEP was alpha-hydroxypalmitic acid. Cells grown at 15 degrees C contained NCAEP, but only traces of HCAEP. By analyzing the incorporation of [1-14C]palmitic acid into cells growing isothermally or shifted from 15 degrees C to 39 degrees C, we obtained evidence favoring a direct conversion of NCAEP to HCAEP. This conversion was blocked in cells grown at 15 degrees C, causing an accumulation of NCAEP. Tetrahymena is a useful model system for studying the poorly understood alpha-hydroxylation process that is of critical importance in myelination of animal nervous tissues.     

The effect of dietary lipids on the thermotropic behaviour of rat liver and heart mitochondrial membrane lipids

Diets supplemented with relatively high levels of either saturated fatty acids derived from sheep kidney fat (sheep kidney fat diet) or unsaturated fatty acids derived from sunflower seed oil (sunflower seed oil diet) were fed to rats for a period of 16 weeks and changes in the thermotropic behaviour of liver and heart mitochondrial lipids were determined by differential scanning calorimetry (DSC). The diets induced similar changes in the fatty acid composition in both liver and heart mitochondrial lipids, the major change being the omega 6 to omega 3 unsaturated fatty acid ratio, which was elevated in mitochondria from animals on the sunflower seed oil diet and lowered with the mitochondria from the sheep kidney fat dietary animals. When examined by DSC, aqueous buffer dispersions of liver and heart mitochondrial lipids exhibited two independent, reversible phase transitions and in some instances a third highly unstable transition. The dietary lipid treatments had their major effect of the temperature at which the lower phase transition occurred, there being an inverse relationship between the transition temperature and the omega 6 to omega 3 unsaturated fatty acid ratio. No significant effect was observed for the temperature of the higher phase transition. These results indicate that certain domains of mitochondrial lipids, probably containing some relatively higher melting-point lipids, independently undergo formation of the solidus or gel phase and this phenomenon is not greatly influenced by the lipid composition of the mitochondrial membranes. Conversely, other domains, representing the bulk of the membrane lipids and which probably contain the relatively lower melting point lipids, undergo solidus phase formation at temperatures which reflect changes in the membrane lipid composition which are in turn, a reflection of the nature of the dietary lipid intake. These lipid phase transitions do not appear to correlate directly with those events considered responsible for the altered Arrhenius kinetics of various mitochondrial membrane-associated enzymes.     

Influence of membrane fluidity changes upon the imprinting of polypeptide hormones in Tetrahymena

Hormonal imprinting is a physiological phenomenon, in which after the first encounter the receptorial and functional responses of a cell change for future occasions. The present experiments demonstrate (using Tetrahymena as a model cell) that the imprinting is very sensitive to the changes in membrane physical state. Cultivation of Tetrahymena cells in 28 or 15 degrees C or in ergosterol-supplemented media caused only quantitative differences in the imprinting; however, the process of cooling (shift-down) or reheating (shift-up) resulted in a false reaction. The combined treatment by ergosterol and cooling completely abolished the imprinting. These results indicate that hormonal imprinting is a membrane-dependent process.     

Modification of membrane lipids. Phenethyl alcohol-induced alteration of lipid composition in Tetrahymena membranes.

Tetrahymena pyriformis NT-I cells in the early-logarithmic phase were incubated with phenethyl alcohol (2-phenylethanol) and effects on the lipid composition were examined in various membranes. 1. There was a marked modification in phospholipid head, as well as fatty acyl group composition in pellicles, mitochondria and microsomes of the phenethyl alcohol-treated cells. Compared with membranes of the control cells, the membranes from phenethyl alcohol-treated cells were found to contain a higher level of phosphatidylcholine content with the compensating decrease in phosphatidylethanolamine, while 2-aminoethylphosphonolipid showed only a slight decrease in these membranes. The acyl group profile of membrane phospholipids in the presence of phenethyl alcohol was also modified so that a profound elevation of the content of polyunsaturated fatty acids, linoleic and gamma-linolenic acids. The major monounsaturate, palmitoleate decreased. Such lipid alteration is a reversible process, and therefore upon removal of phenethyl alcohol the modified lipid composition returned to normal. 2. By freeze-fracture electron microscopy in combination with temperature quenching, the outer alveolar membrane of the phenethyl alcohol-treated cell was observed to reveal less aggregation of intercalated-membrane particles, as compared with the control membrane. The quantitative analysis of the thermotropic lateral movement of membrane particles provided evidence that the membrane in the phenethyl alcohol-treated cell became more fluid. Such fluidizing effects may result from an increase in the acyl group unsaturation and also in the phosphatidylcholine content. 3. With regard to the mechanism responsible for the marked decrease in palmitoleate in membrane phospholipids, there was found a depressed conversion of the palmitate to palmitoleate in the phenethyl alcohol-treated cells. It was further suggested that the drug may have an inhibitory effect on the synthesis of palmitoyl-CoA desaturase involving the (16 : 0 leads to 16 : 1) conversion. Also, it was demonstrated that the increase in a precursor-product fashion of phosphatidylcholine with the corresponding decrease in phosphatidylethanolamine was not due to transformation of phosphatidylethanolamine to phosphatidylcholine through stepwise methylation.     

Effect of the phase state of lipids on their interaction with cobra cytotoxin

Interaction between cytotoxin of the Central Asia cobra venom and dimiristoylphosphatidylcholine bilayer depending on its phase state was studied by ESR with spin label. A conclusion can be drawn that the efficiency of cytotoxin effect on the membranes depends on their phase state. Cytotoxin molecules are incorporated into myophile region of the bilayer, only if the latter is in the liquid crystal state. The interaction between cytotoxins and lipids of the bilayer in a gel state is in the main conditioned by electrostatic forces.     

Age-dependent modifications in membrane lipids: lipid composition, fluidity and palmitoyl-CoA desaturase in Tetrahymena membranes

The membrane lipid composition of Tetrahymena pyriformis NT-I was observed to change in a manner markedly dependent on the progress of culture age. The pellicular, mitochondrial and microsomal membranes were isolated from cell harvested at various growth phases (I, early exponential; II, mid-exponential; III, late exponential; IV, early stationary; V, late stationary) and their lipid composition was analyzed by thin-layer and gas-liquid chromatography. Although the phospholipid composition varied somewhat among membrane fractions, the most general age-dependent alteration was a considerable decrease in the content of phosphatidylethanolamine accompanied by a small increase in phosphatidylcholine. The 2-aminoethylphosphonolipid, enriched in the surface membrane pellicle, did not undergo a consistent change. As for fatty acid composition the most notable variation occurred in unsaturated fatty acids; a great increase in oleic and linoleic acids and a compensatory decrease in palmitoleic acid. This resulted in an augmented unsaturation of the overall phospholipid fatty acid profile of the aged membranes. The age-associated drastic decline in the palmitoleic acid content in membrane phospholipids could be accounted for by the markedly lowered activity of palmitoyl-CoA desaturase. The microsomes from the early exponential phase cells possess a 4-fold higher activity of the desaturase as compared to that of the late stationary phase microsomes. The decreased desaturase activity associated with the culture age was also reflected in the corresponding decrease in the conversion rate of [14C]palmitate to [14C]palmitoleate in cells labelled in vivo. The ESR spectra of the spin-labeled phospholipids extracted from the pellicular and microsomal membranes have led to the suggestion that these types of membrane would become more fluid with the age of growth.     

Temperature-dependent changes in phospholipid and fatty acid composition and membrane lipid fluidity of Yersinia enterocolitica

Temperature-dependent compositional changes of phospholipids and their fatty acids were analysed in Yersinia enterocolitica grown at 5°, 25° and 37°C. The relative amounts of the four phospholipids, phosphatidylethanolamine (75–78%), phosphatidylglycerol (10–11%), cardiolipin (<7%) and lysophosphatidylethanolamine (<5%), were essentially the same at all growth temperatures. The degree of fatty acid unsaturation of the four phospholipids increased with decrease in growth temperature, mainly due to an increase of C_16:1 and C_18:1 and a corresponding decrease of C_16;0, C_18:0 and cyclo C_17:0. An electron spin resonance spectroscopic study of the membrane lipids showed that membrane lipid fluidity was enhanced by decreasing the growth temperatures. The changes in fatty acid composition of phospholipids in response to varied temperatures were consistent with the temperature-dependent changes in the membrane lipid fluidity of Y. enterocolitica , and were similar to those reported for other bacteria.     

Seasonal changes in fast-starts in the short-horn sculpin: integration of swimming behaviour and muscle performance

In short-horn sculpin Myoxocephalus scorpius , the power requirements for fast-start swimming and the length-specific velocity of the curvature wave travelling down the spine ( Û ) were not influenced significantly by acclimation to summer and winter conditions at test temperatures of 5 and 15° C. However, in-vivo and in-vitro muscle performance exhibited acclimation responses at 15° C. Seasonal acclimation altered the escape performance curves for power and Û significantly over a wider temperature range of 0·8–20° C. Û was significantly higher at 20° C in the summer- than winter-acclimation group. The acclimation of lower levels of physiological organization at 15° C may thus serve to extend the thermal limits for escape performance in summer acclimated fish.