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PubMed2004

Membrane order conservation in raft and non-raft regions of hepatocyte plasma membranes from thermally acclimated rainbow trout.

Homeoviscous adaptation (HVA), the thermal conservation of membrane fluidity/order at different body temperatures, has been observed to varying degrees in different membranes. However, HVA has not been studied in raft and non-raft regions of the plasma membrane (PM) separately. Rafts are ordered PM microdomains implicated in signal transduction, membrane traffic and cholesterol homeostasis. Using infrared spectroscopy, we measured order in raft-enriched PM (raft) and raft-depleted PM (RDPM) isolated from hepatocytes of rainbow trout (Oncorhynchus mykiss) acclimated to 5 and 20 degrees C. We found approximately 130% and 90% order compensation in raft and RDPM, respectively, suggesting their independent regulation. Raft was more ordered than RDPM in the warm-acclimated trout, a difference fully explained by a 58% enrichment of cholesterol, compared to RPDM. Unexpectedly, raft and RDPM from cold-acclimated trout did not differ in cholesterol content or order. Freezing the membrane samples during preparation had no effect on order. Treatment with cyclodextrin depleted cholesterol by 36%, 56%, and 55%, producing significant decreases in order in raft and RDPM from warm-acclimated trout and RDPM from cold-acclimated trout, respectively. However, a 69% depletion of cholesterol from raft from cold-acclimated trout had no significant effect on order. This result, and the lack of a difference in order between raft and RDPM, suggests that raft and non-raft PM in cold-acclimated trout are not spatially segregated by phase separation due to cholesterol.

Animals↗
PubMed2004

Thermal acclimation of neonates to prolonged cool exposure as regards sleep stages.

The thermal responses of neonates during a cool acclimation period were studied with regard to sleep stages. Sleep stages, body temperatures and metabolic rate (VO2) were studied for seven neonates nursed in incubators and exposed to a cool temperature (thermoneutrality minus 2 degrees C) for 75 h. Each recording session lasted 3 h in the morning: firstly under thermoneutral baseline conditions, then during the first and last 3-h periods of the cool acclimation and finally during the last 3 h of a 24-h recovery period. Sleep structure was modified during the initial hours of cool exposure: the percentage of active sleep increased (AS: +13%, P = 0.028) at the expense of quiet sleep (QS: -11%, P = 0.043). This alteration in sleep structure persisted at the end of the acclimation period. Metabolic heat production only increased in the later period of cool acclimation. Throughout the cool exposure, VO2 increased more (P = 0.040) in QS (+33%) than in AS (+20%) so that by the end of the cool period, VO2 levels were similar in both sleep stages. During cool acclimation, the maintenance of homeothermy is related not only to a change in sleep organization but also to modifications in the thermoregulatory processes in both sleep stages. Considering the importance of AS/QS patterns in the neurobehavioral development of neonates, the present results could have clinical implications for the thermal management of neonates.

Adaptation, Physiological↗
PubMedDate not supplied

When nonshivering thermogenesis equals maximum metabolic rate: thermal acclimation and phenotypic plasticity of fossorial Spalacopus cyanus (Rodentia).

Many small mammals inhabiting fluctuating and cold environments display enhanced capacity for seasonal changes in nonshivering thermogenesis (NST) and thermoregulatory maximum metabolic rate (MMR). However, it is not known how this plasticity remains in a mammal that rarely experiences extreme thermal fluctuations. In order to answer this question, we determined body mass (m(b)), basal metabolic rate (BMR), NST, MMR, and minimum thermal conductance (C) on a Chilean fossorial caviomorph (Spalacopus cyanus) from a coastal population, acclimated to cold (15 degrees C) and warm (30 degrees C) conditions. NST was measured as the maximum response of metabolic rate (NST(max)) after injection of norepinephrine (NE) in thermoneutrality minus BMR. Maximum metabolic rate was assessed in animals exposed to enhanced heat-loss atmosphere (He-O2) connected with an open-flow respirometer. Body mass and metabolic variables increased significantly after cold acclimation with respect to warm acclimation but to a low extent (BMR, 26%; NST, 10%; and MMR, 12%). However, aerobic scope (MMR/BMR), calculated shivering thermogenesis (ST), and C did not change with acclimation regime. Our data suggest that physiological plasticity of S. cyanus is relatively low, which is in accordance with a fossorial mode of life. Although little is known about MMR and NST in fossorial mammals, S. cyanus has remarkably high NST; low MMR; and surprisingly, a nil capacity of ST when compared with other rodents.

Acclimatization↗
PubMed1999

Effects of thermal acclimation on the relaxation system of crucian carp white myotomal muscle.

Many cyprinid fish are able to compensate for a decrease in ambient temperature by process of physiological adaptation in the function of muscles. In the winter habitat of crucian carp (Carassius carassius L.), low temperature is associated with simultaneous oxygen shortage. Because of the oxygen deprivation, there is probably little space for compensatory adaptation because positive thermal compensation would increase energy demand and accelerate depletion of glycogen reserves. Thus, we assumed that the crucian carp, unlike many other cyprinid fish, would not show positive thermal compensation but either no compensation or inverse compensation in muscle function. To test this hypothesis in the relaxation system of skeletal muscles, we determined the parvalbumin content and the activity of sarcoplasmic reticular (SR) Ca-ATPase in white myotomal muscle of winter- and summer-acclimated crucian carp. In the laboratory, the winter fish were kept at 2 degrees C and the summer fish at 22 degrees C for a minimum of 3 weeks before the experiments. The specific activity of SR Ca-ATPase at low experimental temperature (2 degrees C) was similar in summer- and winter-acclimated fish (0.26 +/- 0.04 vs. 0.25 +/- 0.04 mM/mg/min; P > 0.05). Because of the bigger Q(10) of cold-acclimated carp, the enzyme activity at 30 degrees C was higher in cold-acclimated winter fish than in warm-acclimated summer fish (7.42 +/- 0.90 vs. 5.18 +/- 0.53 mM/mg/min; P < 0.05). In contrast, the yield of SR protein was 70% higher in summer than winter fish (0.315 +/- 0.045 vs. 0.187 +/- 0.017 mg/g; P < 0.001). Because of these opposing changes, total Ca-ATPase activity of SR (per gram muscle weight) remained relatively constant. Similarly, the parvalbumin content of the myotomal muscle was not different between summer (4.09 +/- 0.95 mg/g) and winter (3.70 +/- 0.60 mg/g) fish. Although there were no seasonal changes in the total relaxing system of the crucian carp white myotomal muscle, the same activity of SR Ca-ATPase in winter fish was obtained with less amount of SR pump protein, owing to the increased catalytic activity of the enzyme. The higher catalytic activity of winter fish SR Ca-ATPase might be caused by differences in fatty acid composition noted in membrane lipids; i.e., fewer saturated fatty acids and more n-6 polyunsaturated fatty acids (PUFAs), at the expense of n-3 PUFAs, were present in the SR of cold-acclimated winter fish. Temperature-induced changes in enzyme protein, however, cannot be excluded. Thus, the present results indicate the absence of positive thermal compensation in the relaxing system of crucian carp white muscle. It seems, however, that lipid composition of SR membranes and temperature dependence of SR Ca-ATPase are altered by seasonal acclimation.

Adaptation, Physiological↗
PubMedDate not supplied

Phylogenetic analysis of thermal acclimation of the glycolytic enzymes in the genus Fundulus.

Physiological acclimation that alters enzyme activity can compensate for the effect of temperature on function and may be achieved by altering enzyme concentration. This study uses phylogenetic analyses to investigate the evolutionary history of and to test several hypotheses about acclimation responses among all the glycolytic enzymes. These hypotheses are that (1) acclimation increases enzyme concentration at lower temperatures to compensate for reduced activity; (2) equilibrium enzymes tend to show acclimation responses; and (3) acclimation responses are more common in species whose populations experience either large temporal or geographical temperature variations. Using maximal activities as indices of enzyme concentration, the presence of acclimation responses in all the glycolytic enzymes in the heart ventricle was determined for five species in the teleost genus Fundulus. Three of these species are distributed along the steep thermal cline of the North American Atlantic coast, and thus these species experience both seasonal and geographical variation in temperature. The other two species are found in the Gulf of Mexico and experience seasonal variation similar to the Atlantic species but no geographical variation in temperature. Two Atlantic coast species, Fundulus heteroclitus and Fundulus majalis, have unique derived acclimation responses. No derived acclimation responses occur in the Gulf species. A conserved response in hexokinase was observed within one subgenus comprising both Atlantic and Gulf species. In F. heteroclitus, enolase responded to acclimation, and in F majalis, aldolase, triphosphate isomerase, and lactate dehydrogenase had acclimation responses. These enzymes are equilibrium enzymes, and the concentrations of all of them increase at lower temperatures, which would compensate for the effect of temperature on enzyme activity. The compensatory changes all occur in the Atlantic species and may be a mechanism for species to expand their ranges. These data suggest that physiological acclimation is evolutionarily labile.

Acclimatization↗
PubMed2006

Turning up the heat: the effects of thermal acclimation on the kinetics of hsp70 gene expression in the eurythermal goby, Gillichthys mirabilis.

Most organisms respond to temperature fluctuations by altering the expression of an evolutionarily conserved family of proteins known as heat shock proteins (Hsps). Studies have shown Hsp expression and the activation of HSF1, one of the primary regulators of Hsp transcription, are highly malleable, varying with the recent thermal history of the organism; however, the mechanisms that confer plasticity to the regulation of this ubiquitous response are not well-understood. This study furthers our knowledge in this area by characterizing the activation kinetics of HSF1 and the corresponding transcription of hsp70 in the liver of the eurythermal goby, Gillichthys mirabilis, following a month-long acclimation at 13, 21 or 28 degrees C. Our data revealed HSF1 DNA-binding kinetics varied as a function of acclimation temperature and magnitude/duration of exposure, with gobies acclimated at 21 degrees C exhibiting the most robust response. Hsp70 mRNA followed a similar pattern with induction first occurring in the 13 and 21 degrees C fish, and then most robustly in the 28 degrees C group at 36 degrees C. The hsp70 mRNA induction pattern was corroborated by levels of HSF1 DNA-binding activity in each group and may have been lowest in the 28 degrees C group due to the 2-fold greater levels of hsp70 protein prior to thermal exposure. This study illustrates the integral role of HSF1 as a key regulator of Hsp induction and helps explain the plasticity of this response in ectothermic organisms.

Acclimatization↗
PubMedDate not supplied

Thermal acclimation effects differ between voluntary, maximum, and critical swimming velocities in two cyprinid fishes.

Temperature acclimation may be a critical component of the locomotor physiology and ecology of ectothermic animals, particularly those living in eurythermal environments. Several studies of fish report striking acclimation of biochemical and kinetic properties in isolated muscle. However, the relatively few studies of whole-animal performance report variable acclimation responses. We test the hypothesis that different types of whole-animal locomotion will respond differently to temperature acclimation, probably due to divergent physiological bases of locomotion. We studied two cyprinid fishes, tinfoil barbs (Puntius schwanenfeldii) and river barbels (Barbus barbus). Study fish were acclimated to either cold or warm temperatures for at least 6 wk and then assayed at four test temperatures for three types of swimming performance. We measured voluntary swimming velocity to estimate routine locomotor behavior, maximum fast start velocity to estimate anaerobic capacity, and critical swimming velocity to estimate primarily aerobic capacity. All three performance measures showed some acute thermal dependence, generally a positive correlation between swimming speed and test temperature. However, each performance measure responded quite differently to acclimation. Critical speeds acclimated strongly, maximum speeds not at all, and voluntary speeds uniquely in each species. Thus we conclude that long-term temperature exposure can have very different consequences for different types of locomotion, consistent with our hypothesis. The data also address previous hypotheses that predict that polyploid and eurythermal fish will have greater acclimation abilities than other fish, due to increased genetic flexibility and ecological selection, respectively. Our results conflict with these predictions. River barbels are eurythermal polyploids and tinfoil barbs stenothermal diploids, yet voluntary swimming acclimated strongly in tinfoil barbs and minimally in river barbels, and acclimation was otherwise comparable.

Acclimatization↗
PubMedDate not supplied

[Effect of thermal acclimation on the expression of gene coding for lactate dehydrogenase A4 in loach skeletal muscle].

Acclimation of Misgurnus fossilis to 5 and 18 degrees C induced considerable changes in LDH-A gene expression in white skeletal muscle. Qualities of total and messenger RNA isolated from weighted portions of muscle are considerably higher after acclimation to 18 degrees C as compared to 5 degrees C. However, a PCR assay of cDNA synthesized from these mRNA and equalized by optical density demonstrated that the level of LDH-A gene expression was indistinguishable for high and low acclimation temperatures, while expression of other genes (glyceraldehyde-3-phosphate dehydrogenase and alpha-actin) considerably increased at 18 degrees C as compared to 5 degrees C. The specific enzymatic activity of LDH from white skeletal muscle of the fish acclimated to low temperature is by 20% higher than that for high-temperature acclimation. Structural analysis of the PCR products synthesized on cDNA-5 degrees C and cDNA-18 degrees C has revealed no differences. However, there are indirect indications of the differences in the C-thermal region of the LDH-A molecule. Northern hybridization reveals the differences at the RNA level: one (1400 bp) or two (about 1600 and 1400 bp) hybridization signals have been found in mRNA-5 degrees C and mRNA-18 degrees C, respectively. The presence of two fractions in the mRNA-18 degrees C indicates alternative splicing.

Adaptation, Physiological↗
PubMed2003

Thermal acclimation of surfactant secretion and its regulation by adrenergic and cholinergic agonists in type II cells isolated from warm-active and torpid golden-mantled ground squirrels, Spermophilus lateralis.

Homeothermic mammals experience pulmonary surfactant dysfunction with relatively small fluctuations in body temperature. However, ground squirrels survive dramatic changes in body temperature during hibernation, when body temperature drops from 37 degrees C to 0-5 degrees C during prolonged torpor bouts. Using type II cells isolated from both warm-active and torpid squirrels, we determined the effect of assay temperature, autonomic agonists and torpor on surfactant secretion. Basal secretion was significantly higher in type II cells isolated from torpid squirrels compared with warm-active squirrels when assayed at the body temperature of the animal from which they were isolated (4 degrees C and 37 degrees C, respectively). A change in assay temperature significantly decreased surfactant secretion. However, the change in secretory rate between 37 degrees C and 4 degrees C was less than expected if due to temperature alone (Q(10) range=0.8-1.2). Therefore, the surfactant secretory pathway in squirrel type II cells demonstrates some temperature insensitivity. When incubated at the body temperature of the animal from which the cells were isolated, the adrenergic agonist, isoproterenol, significantly increased surfactant secretion in both warm-active and torpid squirrel type II cells. However, the cholinergic agonist, carbamylcholine chloride, only increased secretion in torpid squirrel type II cells when incubated at 4 degrees C. Torpor did not affect basal cAMP production from isolated type II cells. However, the production of cAMP appears to be upregulated in response to isoproterenol in torpid squirrel type II cells. Thus, at the cellular level, both the secretory and regulatory pathways involved in surfactant secretion are thermally insensitive. Upregulating basal secretion and increasing the sensitivity of type II cells to cholinergic stimulation may be adaptative characteristics of torpor that enable type II cells to function effectively at 0-5 degrees C.

Animals↗
PubMed1979

Enzyme changes accompanying thermal acclimation in two species of pleurocerid snails.

Goniobasis cahawbensis is a stream snail that experiences an annual temperature cycle. G. cochliaris is limited in distribution to springs, and their immediate vicinities, which are characterized by nearly constant annual temperatures. The present study sought to determine whether temperature dependent biochemical differences exist that might account for the differential distribution of these congeneric pleurocerid snails. Eight enzymes were examined following acclimation to 10 degrees, 17 degrees and 24 degrees C. No significant temperature dependent qualitative differences in enzyme phenotypes were demonstrable in either species by starch-gel electrophoresis for malate dehydrogenase, glucose-6-phosphate dehydrogenase, phosphogluconate dehydrogenase, phosphoglucomutase, superoxide dismutase and acetyl and butyryl esterases. Significant quantitative differences were observed in three of these enzymes. G. cahawbensis cytosol malate dehydrogenase activity increased significantly with increasing acclimation temperature, while G. cochliaris malate dehydrogenase activity remained unchanged. The activities of glucose-6-phosphate dehydrogenase did not differ significantly between acclimation temperatures for either species; however, the overall activity of both enzymes was significantly higher for G. cochliaris. Appreciable levels of LDH activity were not demonstrable by electrophoresis or enzymatic assay.

Adaptation, Physiological↗
PubMed1979

Fatty acid and sterol synthesis by hepatocytes of thermally acclimated rainbow trout (Salmo gairdneri).

Incorporation of tritium from tritiated water into lipid fractions was measured in isolated hepatocytes from rainbow trout (Salmo gairdneri) acclimated to 5 degrees C and 20 degrees C. Hepatocytes from cold-acclimated trout exhibited significantly higher rates of tritium incorporation into both fatty acid and sterol fractions at assay temperatures of 15 degrees C and 20 degrees C than did hepatocytes from warm-acclimated trout. Tritium incorporation into the fatty acid fraction was nearly temperature independent in hepatocytes from warm-acclimated trout (Q10 = 1.39) but markedly temperature dependent (Q10 = 2.63) in hepatocytes from cold-acclimated trout; in contrast, rates of sterol synthesis were more temperature dependent in warm-acclimated trout. At 5 degrees C, fatty acid lipogenesis comprised a significantly greater percentage of the total tritium incorporation in hepatocytes from warm-acclimated trout and the percentage of total lipogenesis attributable to fatty acids decreased significantly in warm-acclimated trout as the assay temperature increased; the opposite trends were observed in cold-acclimated trout.

Adaptation, Physiological↗
PubMed1983

The incorporation of unsaturated fatty acids of the n-9, n-6, and n-3 families into individual phospholipids by isolated hepatocytes of thermally-acclimated rainbow trout, Salmo gairdneri.

Rates of incorporation of 1-14C-oleic (18:1n9), -linoleic (18:2n6), and -linolenic (18:3n3) acids into individual phosphatides were determined in isolated hepatocytes from cold (5 degrees C)- and warm (20 degrees C)-acclimated rainbow trout, Salmo gairdneri. Fatty acid incorporation into phosphatidylcholine (PC) exceeded that into all other phospholipids, but at assay and acclimation temperatures of 5 degrees C, incorporation into phosphatidylethanolamine (PE) was generally intermediate between that of PC and the remaining phosphatides. Specific radioactivities (ratios of percentage isotope incorporation-to-mole percentage of phosphatide) were consistently less than one for both PC and PE, and greater than one for phosphatidic acid (PA), lysophosphatidylcholine (LPC), phosphatidylserine (PS), and cardiolipin (CL). For PS, specific radioactivities were greater in cold- than warm-acclimated trout, and greater at 5 degrees C than 20 degrees C. Rates of oleate incorporation were generally higher, and rates of incorporation of 18:2 and 18:3 lower in cold- than warm-acclimated trout. Most phospholipids demonstrated a clear preference for the incorporation of 18:2 when assayed at 20 degrees C; however, at 5 degrees C the incorporation of 18:2 was reduced and 18:3 was generally the preferred substrate. A reduction in assay temperature from 20 degrees C to 5 degrees C also shifted the incorporation of 18:2 away from PC into PS and PA. These data were interpreted to indicate 1) a cold-induced activation of PS metabolism, possibly resulting in elevated levels of PE; 2) lower rates of general acyl group turnover in animals acclimated to 5 degrees C than 20 degrees C; 3) a specificity to the acclimation response that favors the incorporation at cold temperatures of polyunsaturated fatty acids, but not the parent acids from which they are derived; and 4) the participation of a deacylation-reacylation cycle in the metabolism of phospholipids, particularly at cold temperatures.

Adaptation, Physiological↗
PubMed2000

Structure-function relationships of the two surface loops of myosin heavy chain isoforms from thermally acclimated carp.

The structure-function relationships of fast skeletal myosin isoforms remain poorly understood. To shed some light, we constructed chimeric myosins comprised of Dictyostelium myosin heavy chain backbone with carp loop sequences and analyzed their functional properties. A loop 2-10 chimeric myosin having the loop 2 sequence of the fast skeletal isoform predominantly expressed in carp acclimated to 10 degrees C showed V(max) in actin-activated Mg(2+)-ATPase activity 1.4-fold higher than a loop 2-30 chimera constructed from the loop 2 sequence of the dominant isoform in carp acclimated to 30 degrees C. These two chimera exhibited no significant differences in sliding velocity of actin filaments in in vitro motility assay. Contrastingly, both loop 1-associated chimeras, loop 1-10 and loop 1-30, did not differ in both ATPase activity and in sliding velocity of actin filaments.

Acclimatization↗
PubMed1985

Partial purification and kinetic characterization of the microsomal phospholipase A2 from thermally acclimated rainbow trout (Salmo gairdneri).

Phospholipase A2 (PLA2) was extracted from liver microsomal membranes of both 5 and 20 degrees C-acclimated rainbow trout (Salmo gairdneri), using the non-ionic detergent, Triton X-100. Further purification was achieved by precipitation with 35-65% ammonium sulfate followed by gel filtration chromatography in the presence of 0.1% Triton X-100 on Sephadex G-200. These procedures resulted in a 30-fold purification and the removal of all traces of phospholipid from the enzyme of both warm- and cold-acclimated trout. Column elution profiles were similar for both acclimation groups, yielding a molecular weight estimate for the trout liver enzyme of 73,000. Comparisons of activity levels and kinetic parameters of PLA2 from warm- and cold-acclimated fish indicated that compensation for temperature at non-saturating substrate concentrations was an attribute of both the particulate (microsomal) enzyme and the lipid-free protein. Cold acclimation resulted in higher activity below Vmax due primarily to decreased apparent Km values. These adaptations to temperature could not be attributed to the interaction of the enzyme with the membrane lipids, but were due to qualitative changes in the enzyme that resulted from acclimation. Other adaptive qualities of PLA2, such as reduced Km in response to acute decreases in temperature in warm-acclimated fish, were only apparent in particulate preparations, and thus were a function of the protein-lipid complex. These data suggest that an acclimation-induced increase in the activity of PLA2 may result in the activation of a deacylation-reacylation cycle at cold temperatures.

Acclimatization↗
PubMed1995

Thermal acclimation and dietary lipids alter the composition, but not fluidity, of trout sperm plasma membrane.

The effect of a long-term adaptation of rainbow trout to 8 and 18 degrees C combined with a corn oil- or a fish oil-supplemented diet on the characteristics of the spermatozoan plasma membrane was investigated. The experiment lasted up to 22 mon during which spermatozoa were collected from the mature males. Spermatozoan plasma membranes were isolated by nitrogen cavitation, and the cholesterol content, phospholipid composition and fatty acid pattern were investigated. Membrane viscosity was assessed on whole cells by electron spin resonance using spin-labeled phospholipids. Neither diet nor rearing temperature influenced the cholesterol content of the plasma membrane nor the phospholipid class distribution. The rearing temperature of the broodstock only slightly affected the phospholipid fatty acids. A minor decrease in 18:0 and increase in monounsaturated fatty acids was observed for the cold-adapted fish. These modifications were not sufficient to affect membrane fluidity, and we conclude that trout spermatozoa do not display any homeoviscous adaptations in these conditions. On the contrary, the dietary fatty acid intake greatly modified the fatty acid profile of plasma membrane phospholipids. The fish oil-fed trout displayed a much higher n-3/n-6 fatty acid ratio than did the corn oil-fed ones, but the 22:6n-3 levels remained unchanged. Modifications in plasma membrane composition by the diet were obtained although neither of the two diets was deficient in essential fatty acids. The enrichment in n-3 fatty acids, however, did not affect plasma membrane fluidity which was unchanged by the diets.

Acclimatization↗
PubMed1999

Influences of subzero thermal acclimation on mitochondrial membrane composition of temperate zone marine bivalve mollusks.

The phospholipid and phospholipid fatty acid composition of gill mitochondrial membranes from two temperate zone marine bivalve mollusks, the quahog, Mercenaria mercenaria, and the American oyster, Crassostrea virginica, were examined after acclimation to 12 and -1 degree C. Cardiolipin (CL) was the only phospholipid with proportions altered upon acclimation to -1 degree C, increasing 188% in the mitochondrial membranes of M. mercenaria. Although the ratio of bilayer stabilizing to destabilizing lipids is frequently associated with cold acclimation in ectothermic species, no change was found in this ratio in either of the species. Polyunsaturated fatty acids (PUFA) were found only to increase in C. virginica with cold acclimation, with total n-3 PUFA increasing in the phospholipid phosphatidylethanolamine, total n-6 PUFA increasing in CL, and total PUFA increasing in phosphatidylinositol. Monounsaturated fatty acids, not PUFA, were found to have increased in M. mercenaria, with 18:1 n-9 increasing by 150% in CL, and 20:1 increasing in both CL and phosphatidylcholine, by 146 and 192%, respectively. These manipulations of membrane phospholipid and fatty acid composition may represent an attempt by these species to help maintain membrane function at low temperatures.

Adaptation, Physiological↗
PubMed1980

A steady state and differential polarised phase fluorimetric study of the liver microsomal and mitochondrial membranes of thermally acclimated green sunfish (Lepomis cyanellus).

The liver mitochondrial and microsomal membranes of green sunfish and rat were examined by steady state polarisation and differential polarised phase fluorimetry to determine the effects of seasonal adaptation of membrane dynamic structure to temperature. Steady state polarisation studies indicated that the liver mitochondria of green sunfish acclimated to different temperatures showed a greater partial compensation of membrane fluidity for the fatty acid composition of both membrane preparations generally became more unsaturated at lower acclimation temperatures, though the differences between 5 degrees C and 25 degrees C acclimated fish were more pronounced in the mitochondrial fraction than in the microsomal fraction. Differential polarised phase fluorimetric studies indicated that the rotations of diphynylhexatriene in mitochondrial and microsomal membranes were highly hindered, though the hindrance offered by membranes of 25 degrees C acclimated green sunfish was far greater than that offered by the membranes of 5 degrees C acclimated fish, thus supporting the concept of homeoviscous adaptation. The absolute rotational rate was not consistently affected by acclimation treatment.

Acclimatization↗