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At least 19 recordsLinked to original sources
PubMed1994

Urea and salt effects on enzymes from estivating and non-estivating amphibians.

The effects of urea, cations (K+,NH4,Na+,Cs+,Li+), and trimethylamines on the maximal activities and kinetic properties of pyruvate kinase (PK) and phosphofructokinase (PFK) from skeletal muscle were analyzed in two anuran amphibians, an estivating species, the spadefoot toad Scaphiopus couchii, and a semi-aquatic species, the leopard frog Rana pipiens. Urea, which accumulates naturally to levels of 200-300 mM during estivation in toads, had only minor effects on the Vmax, kinetic constants and pH curves of PK from either species and no effects on PFK Vmax or kinetic constants. Trimethylamine oxide neither affected enzyme activity directly or changed enzyme response to urea. By contrast, high KCl (200 mM) lowered the Vmax of toad PFK and of PK from both species and altered the Km values for both substrates of frog PFK. Other cations were even more inhibitory; for example, the Vmax of PK from either species was reduced by more than 80% by the addition of 200 mM NH4Cl, NaCl, CsCi, or LiCl. High KCl also significantly changed the Km values for substrates of toad lactate dehydrogenase and strongly reduced the Vmax of glutamate dehydrogenase and NAD-dependent isocitrate dehydrogenase in both species whereas 300 mM urea had relatively little effect on these enzymes. The perturbing effect of urea on enzymes and the counteracting effect of trimethylamines that has been reported for elasmobranch fishes (that maintain high concentrations of both solutes naturally) does not appear to apply to amphibian enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2005

Physiological responses to feeding, fasting and estivation for anurans.

Anuran estivation is characterized by long episodes of aphagia. To investigate whether estivating anurans downregulate intestinal performance as an adaptive mechanism to reduce energy expenditure, I compared the metabolic and intestinal responses to feeding, fasting and estivation among non-estivating and estivating species of the anuran families Bufonidae, Leptodactylidae and Ranidae. Standard metabolic rates of the estivating Bufo alvarius, Ceratophrys ornata and Pyxicephalus adspersus were significantly less than those of the non-estivating Bufo marinus, Leptodactylus pentadactylus and Rana catesbeiana. Whereas the digestion of rodent meals equaling 15% of anuran body mass generated significant metabolic responses for all species, specific dynamic action was significantly greater for the estivating species. For estivating species, feeding triggered more than a doubling of small intestinal mass and significant upregulation of intestinal nutrient transport rates, resulting in six- to tenfold increases in total intestinal nutrient uptake capacity. The postprandial intestinal responses of the non-estivating species were much more modest, averaging a 50% increase in small intestinal mass and 69% increase in uptake capacities. Following 1 month of laboratory-induced estivation, C. ornata and P. adspersus had further depressed metabolic rates by 20%, intestinal masses by 44%, and total intestinal uptake capacities by 60%. In a fashion similar to infrequently feeding, sit-and-wait foraging snakes, estivating anurans possess the capacity to severely downregulate intestinal performance with fasting and estivation, and subsequently upregulate the gut with feeding. The depression in gut performance during estivation aids in reducing energy expenditure, thereby increasing the duration that the animal can remain dormant while relying solely upon stored energy.

Analysis of Variance↗
PubMed2006

Suppression of Na+/K+-ATPase activity during estivation in the land snail Otala lactea.

Entry into the hypometabolic state of estivation requires a coordinated suppression of the rate of cellular ATP turnover, including both ATP-generating and ATP-consuming reactions. As one of the largest consumers of cellular ATP, the plasma membrane Na+/K+-ATPase is a potentially key target for regulation during estivation. Na+/K+-ATPase was investigated in foot muscle and hepatopancreas of the land snail Otala lactea, comparing active and estivating states. In both tissues enzyme properties changed significantly during estivation: maximal activity was reduced by about one-third, affinity for Mg.ATP was reduced (Km was 40% higher), and activation energy (derived from Arrhenius plots) was increased by approximately 45%. Foot muscle Na+/K+-ATPase from estivated snails also showed an 80% increase in Km Na+ and a 60% increase in Ka Mg2+ as compared with active snails, whereas hepatopancreas Na+/K+-ATPase showed a 70% increase in I50 K+ during estivation. Western blotting with antibodies recognizing the alpha subunit of Na+/K+-ATPase showed no change in the amount of enzyme protein during estivation. Instead, the estivation-responsive change in Na+/K+-ATPase activity was linked to posttranslational modification. In vitro incubations manipulating endogenous kinase and phosphatase activities indicated that Na+/K+-ATPase from estivating snails was a high phosphate, low activity form, whereas dephosphorylation returned the enzyme to a high activity state characteristic of active snails. Treatment with protein kinases A, C or G could all mediate changes in enzyme properties in vitro that mimicked the effect of estivation, whereas treatments with protein phosphatase 1 or 2A had the opposite effect. Reversible phosphorylation control of Na+/K+-ATPase can provide the means of coordinating ATP use by this ion pump with the rates of ATP generation by catabolic pathways in estivating snails.

Adenosine Triphosphate↗
PubMed1998

Antioxidant defenses and lipid peroxidation damage in estivating toads, Scaphiopus couchii.

Tissue-specific changes in antioxidant defenses and lipid peroxidation damage were analyzed in spadefoot toads, Scaphiopus couchii, to determine how these responded during estivation, a state of suppressed oxygen consumption. Maximal activities of glutathione-S-transferase, glutathione reductase, glutathione peroxidase, superoxide dismutase and catalase were measured in six organs from 2-month-estivated toads and compared with activities in animals awakened for 10 days after estivation. Activities of many enzymes, particularly the glutathione-linked enzymes, were significantly lower in tissues of estivating toads than in awake toads. This indicates that enzymatic antioxidant defenses are probably modulated in response to the rate of reactive oxygen species generation in tissues, which is proportional to oxygen consumption. Antioxidant enzyme activities were largely insensitive to high urea, which accumulates during estivation, but were inhibited by elevated KCl. Levels of reduced glutathione were also significantly lower in three organs during estivation and all organs, except skeletal muscle, exhibited a higher oxidized/reduced glutathione ratio, indicating a more oxidized state during estivation. Products of lipid peroxidation (conjugated dienes, lipid hydroperoxides) were higher in tissues of estivated than control toads, suggesting accumulated oxidative damage to lipids during dormancy. One enzymatic source of free radical generation, xanthine oxidase, appeared to have little impact because its activity was detectable only in liver and was significantly lower in estivated toads. The data indicate that both enzymatic and metabolite antioxidant defenses in toads are adaptable systems that are modulated in estivating versus awake states.

Animals↗
PubMed2002

Studies on the extra- and intracellular acid-base status and its role on metabolic depression in the land snail Helix lucorum (L.) during estivation.

The aim of the present study was to examine the acid-base status of extra- and intracellular fluids and its possible role on the regulation of the metabolic rate of Helix lucorum during prolonged estivation. For this purpose, the rate of oxygen consumption for active and estivating snails was determined. The acid-base status was also examined in the hemolymph and tissues from active and estivating snails acclimated at 25 degrees C. In addition, the buffer values of hemolymph and tissues were determined in order to examine whether there is a change in the snails during estivation. The rate of oxygen consumption decreased significantly within the 1st 10 days of estivation from 122.51+/-10 microl.g(-1).h(-1) to 25.86+/-5.2 microl.g(-1).h(-1), indicating a marked decrease in metabolic rate. P(CO2)increased within the 1st 20 days of estivation from 13.52+/-0.68 mmHg to 25.09+/-2.05 mmHg, while the pH of hemolymph (pH(e)) decreased from 7.72+/-0.04 to 7.44+/-0.06. The level of bicarbonates decreased in the hemolymph of estivating snails, indicating a metabolic acidosis, which was moderate in extracellular fluids. In contrast to pH(e), the intracellular pH (pH(i)) was maintained in the tissues of estivating H. lucorum, indicating a regulation of pH(i) despite the developed hypercapnia. According to the results presented here, it seems that the timing of pH(e) changes does not correlate with the timing of metabolic rate reduction in estivating H. lucorum.

Acid-Base Equilibrium↗
PubMed1976

Respiratory properties of blood in awake and estivating lungfish, Protopterus amphibius.

Blood respiratory properties have been studied in awake and estivating African lungfish, Protopterus amphibius. Fish had been estivating 28-30 months when blood was sampled. Hematocrit, O2 capacity and blood hemoglobin concentration increased by about 50% during estivation. Red cell Hb concentration (MCHC) was unaltered. Total blood concentration of nucleoside triphosphates (NTP) was reduced 50% in estivation. Thin-layer chromatography showed that the change in NTP resulted from a GTP/Hb (guanosine triphosphate) reduction to 20% of the value in awake fish. ATP (adenosine triphosphate) concentration remained largely unaltered. GTP/Hb changes were accompanied by marked changes in O2 affinity. The P50 value in blood from awake fish was 33 mm Hg at pH 7.5 compared to 9 mm Hg for the estivating fish. The n-value changed insignificantly. An increased Bohr effect was present in estivating fish, but its importance will depend on circulating pH in the two states. Standard bicarbonate ranged from a low of 8.6 mMol-L-1 (P plasma) at pH 7.5 in an awake fish to 49.6 mMol-L-1 (P) in an estivating fish. CO2 dissociation curves showed a variable Haldane effect having its highest value in the in vivo range of PCO2. The striking increase in O2-Hb affinity during estivation is regarded as an adaptation to a reduced alveolar O2 availability associated with estivation. Altered mechanics of pulmonary ventilation and reduced ambient O2 availability caused by the subterranean habitat may have been selection pressures for the development of the high O2 availability caused by the subterranean habitat may have been selection pressures for the development of the high O2 affinity. The mechanism behind it rests with the recorded change in erythrocytic concentration of GTP.

Adaptation, Physiological↗
PubMed2002

Life in the slow lane: molecular mechanisms of estivation.

Estivation is a state of aerobic hypometabolism used by organisms to endure seasonally arid conditions, often in desert environments. Estivating species are often active for only a few weeks each year to feed and breed and then retreat to estivate in sheltered sites, often underground. In general, estivation includes a strong reduction in metabolic rate, a primary reliance on lipid oxidation to fuel metabolism, and methods of water retention, both physical (e.g. cocoons) and metabolic (e.g. urea accumulation). The present review focuses on several aspects of metabolic adaptation during estivation including changes in the activities of enzymes of intermediary metabolism and antioxidant defenses, the effects of urea on estivator enzymes, enzyme regulation by reversible protein phosphorylation, protein kinases and phosphatases involved in signal transduction mechanisms, and the role of gene expression in estivation. The focus is on two species: the spadefoot toad, Scaphiopus couchii, from the Arizona desert; and the land snail, Otala lactea, a native of the Mediterranean region. The mechanisms of metabolic depression in estivators are similar to those seen in hibernation and anaerobiosis, and contribute to the development of a unified set of biochemical principles for the control of metabolic arrest in nature.

Adaptation, Physiological↗
PubMed1999

Reversible phosphorylation control of skeletal muscle pyruvate kinase and phosphofructokinase during estivation in the spadefoot toad, Scaphiopus couchii.

Both pyruvate kinase (PK) and phosphofructokinase (PFK) occur in two different forms, separable by isoelectric focusing (IEF), in skeletal muscle of the spadefoot toad Scaphiopus couchii. During estivation (aerobic dormancy) the proportions of the two forms changed compared with controls; in both cases the amount of enzyme in Peak I (pI = 5.3-5.4) decreased whereas activity in Peak II (isoelectric point = 6.2-6.4) increased. In vitro incubation of crude muscle extracts with 32P-ATP under conditions that promoted the activity of cAMP-dependent protein kinase led to strong radiolabeling associated with Peak I, but not Peak II, and reverse phase HPLC confirmed that 32P was associated with the subunits of both PK and PFK found in Peak I. Specific radiolabeling of Peak I PK and PFK by protein kinase A was further confirmed using immunoprecipitation. In total, this information allowed identification of the Peaks I and II enzymes as the phosphorylated and dephosphorylated forms, respectively, and the effect of estivation was to increase the proportion of dephosphorylated PK and PFK in muscle. Analysis of the kinetic properties of partially purified PK and PFK revealed significant kinetic differences between the two forms of each enzyme. For PK, the Peak II (low phosphate) enzyme showed a 1.6-fold higher Km for phosphoenolpyruvate and a 2.4-fold higher Ka for fructose-1,6-bisphosphate than did the Peak I (high phosphate) form. These kinetic properties suggest that Peak II PK is the less active form, and coupled with the shift to predominantly the Peak II form during estivation (87% Peak II vs. 13% Peak I), are consistent with a suppression of PK activity in estivating muscle, as part of the overall metabolic rate depression of the estivating state. A similar shift to predominantly the Peak II, low phosphate, form of PFK (75% Peak II, 25% Peak I) in muscle of estivating animals is also consistent with metabolic suppression since phosphorylation of vertebrate skeletal muscle PFK is typically stimulated during exercise to enhance enzyme binding to myofibrils in active muscle. Peak II PFK also showed reduced sensitivity to inhibition by Mg:ATP (I50 50% higher) compared with the Peak I form suggesting that the enzyme in estivating muscle is less tightly regulated by cellular adenylate status than in awake toads. The data indicate that reversible phosphorylation control over the activity states of enzymes of intermediary metabolism is an important mechanism for regulating transitions between dormant and active states in estivating species.

Animals↗
PubMed2001

Tyrosine kinases and phosphatases in the estivating spadefoot toad.

To endure seasonally arid conditions, spadefoot toads (Scaphiopus couchii) spend 9-10 months underground each year in a hypometabolic state, termed estivation. Protein tyrosine kinases (PTKs) and phosphatases (PTPs) were evaluated in organs of control and estivating toads to assess their possible role in signal transduction during estivation. Total PTK activity decreased by 27-52 % in liver, lung and skeletal muscle during estivation but rose by 66% in heart. Total PTP activity changed only in liver (55 % decrease) and heart (74 %increase). Analysis of the distribution of PTKs between cytoplasmic and membrane-associated forms showed that estivation-linked changes in both fractions occurred in heart (increase) and liver (decrease) whereas in lung and skeletal muscle only the soluble fraction was affected. PTPs were assessed using both a general substrate (ENDpYINASL) and a substrate (DADEpYLIPQQG) specific for PTPs containing the SH2 binding site; both revealed estivation-associated changes in activities and subcellular distribution of PTPs in all tissues. DEAE-Sephadex chromatography showed multiple forms of skeletal muscle PTKs and PTPs in both soluble and insoluble fractions. Each fraction showed three major peaks of PTK activity, two of which shifted in elution position during estivation. The data show that PTKs and PTPs are modified in an organ-specific fashion during estivation by three mechanisms: changes in total activity, changes in subcellular distribution and possible protein covalent modification.

Animals↗
PubMed1998

Remodeling of phospholipid fatty acids in mitochondrial membranes of estivating snails.

The effects of estivation on the phospholipid-specific fatty acid composition of mitochondrial membranes in the hepatopancreas of the terrestrial snail Cepaea nemoralis were investigated. The fatty acid composition of all phospholipids was significantly altered in snails estivating for 6 wk, indicating that substantial remodeling occurs. The most profound changes occurred in cardiolipin (CL). CL of estivating snails was 13-fold more saturated, contained 9-fold more monoenes, and had 45% fewer polyenes than in active snails. These differences were due, in part, to a reduction in linoleic acid (1 8:2n-6) content of CL from estivators. As in mammals, CL of active snails appears to preferentially incorporate 18:2n-6, which accounts for 60% of the acyl chains in this phospholipid. This proportion was reduced by 50% in estivators. Changes in the fatty acyl content of other phospholipids of estivating snails included increased monoenes in phosphatidylethanolamine (PE) and phosphatidylinositol, reduced ratios of n-3/n-6 polyenes in PE and phosphatidylcholine (PC), and an increased n-3/n-6 ratio in phosphatidylserine (PS). Arachidonic acid (20:4n-6) levels were reduced in PS but increased in CL and PC. Taken together, these alterations to fatty acid composition are consistent with decreased biological activity of membrane-related processes which occur in conjunction with the reduction of mitochondrial aerobic metabolism observed during estivation.

Animals↗
PubMed2005

Nitrogen metabolism and excretion in the swamp eel, Monopterus albus, during 6 or 40 days of estivation in mud.

Monopterus albus inhabits muddy ponds, swamps, canals, and rice fields, where it can burrow into the moist earth, and it survives for long periods during the dry summer season. However, it had been reported previously that mortality increased when M. albus was exposed to air for 8 d or more. Thus, the objective of this study was to elucidate the strategies adopted by M. albus to defend against ammonia toxicity during 6 or 40 d of estivation in mud and to evaluate whether these strategies were different from those adopted by fish to survive 6 d of aerial exposure. Ammonia and glutamine accumulations occurred in the muscle and liver of fish exposed to air (normoxia) for 6 d, indicating that ammonia was detoxified to glutamine under such conditions. In contrast, ammonia accumulation occurred only in the muscle, with no increases in glutamine or glutamate contents in all tissues, of fish estivated in mud for 6 d. Similar results were obtained from fish estivated in mud for 40 d. While estivating in mud prevented excessive water loss through evaporation, M. albus was exposed to hypoxia, as indicated by significant decreases in blood P(O(2)), muscle energy charge, and ATP content in fish estivated in mud for 6 d. Glutamine synthesis is energy intensive, and that could be the reason why M. albus did not depend on glutamine synthesis to defend against ammonia toxicity when a decrease in ATP supply occurred. Instead, suppression of endogenous ammonia production was adopted as the major strategy to ameliorate ammonia toxicity when M. albus estivated in mud. Our results suggest that a decrease in O(2) level in the mud could be a more effective signal than an increase in internal ammonia level during aerial exposure to induce a suppression of ammonia production in M. albus. This might explain why M. albus is able to estivate in mud for long periods (40 d) but can survive in air for only <10 d.

Adenosine Triphosphate↗
PubMedDate not supplied

Profile of organic acid concentrations in the digestive gland and hemolymph of Biomphalaria glabrata under estivation.

Using high performance liquid chromatography (HPLC) analysis it was possible to determine simultaneously the concentration of organic acids (pyruvate, lactate, succinate, fumarate, malate, acetate, propionate, acetoacetate, and ss-hydroxybutyrate) in the digestive gland and the extracellular concentration of these same acids in the hemolymph of estivating Biomphalaria glabrata, the intermediate host of Schistosoma mansoni. After a 7 day period of estivation, there was a significant increase in the tissue levels of lactate, succinate, malate and acetate compared to non-estivating snails. After 14 days of estivation, the levels of lactate and acetate were also significantly elevated. The hemolymph concentrations of pyruvate and acetate increased significantly after 7 days and acetate concentrations continued to be significantly increased up to 14 days of estivation. The other organic acids studied, such as ketone body acetoacetate and ss-hydroxybutyrate or the volatile acid propionate, did not accumulate. Their tissue concentrations, however, increased on the 7th day of estivation and reached normal levels within two weeks of estivation for some of them. One should take into consideration how the reduction in metabolism can be handled under aerobic conditions, and what role anaerobic pathways may play in both energy formation and redox balance processes.

Acids↗
PubMed1990

Reduction of thyrotropin-releasing hormone concentrations in central nervous system of African lungfish during estivation.

Thyrotropin-releasing hormone (TRH) has been implicated as an important modulator of arousal state in mammals. Changes in the content of TRH in several brain regions accompany hibernation in the ground squirrel. In the present study, the involvement of TRH in the regulation of arousal was further investigated in the African lungfish, Protopterus annectens, which contain high concentrations of TRH throughout its central nervous system and enter a hibernation-like state, estivation. Lungfish were divided into three groups. Group 1 was fed normally, group 2 was starved while aquatic, and group 3 was allowed to enter into a state of estivation. After 3 months, the lungfish were sacrificed and the concentrations of TRH, norepinephrine, dopamine, and serotonin were determined in the telencephalon, diencephalon, medulla, and spinal cord. In estivation, there was a significant decline in the concentration of TRH in the diencephalon, with no alteration in other regions. Starvation had no effect on regional TRH concentrations. The concentration of norepinephrine, dopamine, and serotonin did not change in estivation; however, a significant elevation of norepinephrine in the diencephalon and dopamine in the telencephalon was observed in starvation. Starvation and estivation were associated with significant declines in the protein content of the diencephalon and medulla. The estivation-linked decline in TRH in the diencephalon of the lungfish is similar to the decrease in TRH content in the hypothalamus in hibernating ground squirrels. These findings lend further support to the importance of TRH in the regulation of arousal state.

Adaptation, Physiological↗
PubMed2003

The role of eukaryotic initiation factor 2alpha during the metabolic depression associated with estivation.

We have investigated the role of eukaryotic initiation factor 2alpha (eIF2alpha) in two estivating organisms previously shown to downregulate protein synthesis during metabolic depression, the land snail Helix aspersa Müller and the desert frog Neobatrachus sutor Main 1957. We have developed a method using a single antibody (which binds specifically to the phosphorylated, conserved phosphorylation region) by which the total levels of eIF2alpha and the ratio of phosphorylated eIF2alpha [eIF2alpha(P)] to total (phosphorylated and unphosphorylated) eIF2alpha can be determined. In H. aspersa, we have shown that the level of eIF2alpha mRNA expression is unchanged between the awake and estivating states. The amount of total eIF2alpha is the same in the estivating and awake states, and eIF2alpha(P) is undetectable and must represent < or =10% of total eIF2alpha in both states. Conversely, in N. sutor during estivation, the level of total eIF2alpha increases approximately 1.6-fold and the ratio of eIF2alpha(P)/eIF2alpha increases from 0.22+/-0.11 to 0.52+/-0.08, implicating eIF2alpha phosphorylation in the downregulation of protein synthesis during estivation in this animal. The differences in the amounts of eIF2alpha and the level of its phosphorylation between these two species also suggest possible differences either in the mechanism by which protein synthesis is downregulated during estivation or in the sensitivity of the initiation of translation to eIF2alpha(P) levels.

Amino Acid Sequence↗
PubMed1999

Gene expression during estivation in spadefoot toads, Scaphiopus couchii: upregulation of riboflavin binding protein in liver.

A cDNA library constructed from liver of 2-month estivating female spadefoot toads, Scaphiopus couchii, was differentially screened to reveal genes that were induced or upregulated during estivation. After two rounds of screening a clone was isolated that showed 60% higher expression in liver of estivating, versus control, toads. The clone possessed a 1.0 kb insert which annealed to a single 0.7 kb band on Northern blots. Sequencing revealed a 1053 nucleotide full-length cDNA; the largest potential open reading frame was 708 nucleotides which encoded a protein of 235 amino acids. A homology search in Genbank indicated that the protein was a riboflavin binding protein (RfBP), a monomeric phosphoglycoprotein produced by the liver of female birds, reptiles, and mammals that functions to bind plasma riboflavin and load the vitamin into eggs or fetus. To our knowledge, this is the first demonstration that RfBP is also present in amphibians. Toad RfBP showed 50% of residues identical with the chicken or turtle liver proteins and many essential structural features were conserved in the toad protein including 18 cysteine residues, two asparagine glycosylation sites, and 6 tryptophan residues. However, a region with eight phosphoserines in the chicken or turtle proteins that functions in RfBP binding to the oocyte membrane contained only three serine residues in toad RfBP, suggesting that recognition and binding to oocyte receptors must be different in toads. Northern hybridization showed that toad RfBP was largely liver-specific; no mRNA transcripts were detected in brain, gut, heart, or kidney but low message levels occurred in hind leg skeletal muscle of estivating, but not control, toads. Upregulation of RfBP in liver of estivating toads may be linked with maturation of eggs in preparation for the explosive breeding that occurs immediately upon emergence from estivation but might also have a role for the adult in "caching" riboflavin to maintain an endogenous vitamin pool over the 9-10 months of each year that toads are dormant.

Amino Acid Sequence↗
PubMed2006

Thin layer chromatographic analysis of glucose and maltose in estivated Biomphalaria glabrata snails and those infected with Schistosoma mansoni.

Thin layer chromatography was used to analyze the glucose and maltose concentrations of the digestive gland-gonad complex (DGG) of uninfected-estivated Biomphalaria glabrata snails and estivated B. glabrata patently infected with Schistosoma mansoni. All snails were estivated in a most chamber at a relative humidity of 98+/-1% and a temperature of 23+/-1 degrees C for 14 days. Carbohydrates were extracted from the DGG with 70% aqueous ethanol, and extracts were analyzed on silica gel preadsorbent plates using ethyl acetate-glacial acetic acid-methanol-water (60:15:15:10) mobile phase, alpha-naphthol-sulfuric acid detection reagent, and quantification by densitometry. The concentrations of glucose and maltose were significantly reduced in both uninfected-estivated snails and infected-estivated snails.

Animals↗
PubMed2005

Seasonal modulation of free radical metabolism in estivating land snails Helix aspersa.

We investigated the regulation of free radical metabolism in Helix aspersa snails during a cycle of 20-day estivation and 24-h arousal in summer in comparison with estivation/arousal in winter-snails. In winter-snails (J. Exp. Biol. 206, 675-685, 2003), we had already observed an increase in the selenium-dependent glutathione-peroxidase (Se-GPX) activity in foot muscle and hepatopancreas and in the contents of hepatopancreas GSH-equivalents (GSH-eq=GSH+2 GSSG) during estivation compared with 24-h aroused snails. Summer-estivation prompted a 3.6-fold increase in Se-GPX activity in hepatopancreas, though not in foot muscle. Total-superoxide dismutase and catalase activities in hepatopancreas decreased (by 30-40%) during summer-estivation; however, no changes occurred in the activities of glutathione reductase, glutathione S-transferase and glucose-6-phosphate dehydrogenase in the two organs. GSH-eq levels were increased (by 54%) in foot muscle during estivation, but were unchanged in hepatopancreas. In contrast with winter-snails, oxidative stress markers (lipid peroxidation, carbonyl protein, and the GSSG/GSH-eq ratio) were unaltered during estivation/arousal in summer. These results demonstrate that seasonality modulates not only the absolute activities/levels of antioxidants (enzymes and GSH-eq) in H. aspersa, but also the regulatory process that controls the snail's antioxidant capacity during estivation/arousal. These results suggest that H. aspersa has an "internal clock" controlling the regulation of free radical metabolism in the different seasons.

Animals↗
PubMed1998

Compositional correlates of metabolic depression in the mitochondrial membranes of estivating snails.

The phospholipid and protein compositions of mitochondrial membranes from hepatopancreas of active and estivating terrestrial snails (Cepaea nemoralis) were compared. Mitochondria from estivating snails contained 82.7% less cardiolipin, and this was associated with an 83.9% reduction in cytochrome-c oxidase activity. Substantial changes also occurred in the proportional amounts of other individual phospholipid classes and their constituent fatty acids, including a 72% loss of total mitochondrial phospholipids, a 37% increase in monoenes, and 49% fewer n-3 fatty acids in membranes of estivating snails. These changes are consistent with those correlated with lowered metabolic rate and lower rates of proton leak in other animal models. Estivating snail hepatopancreas showed no change in total phospholipid content, indicating that the phospholipids lost from mitochondrial membranes may be sequestered elsewhere within the cell. We suggest that estivating snails remodel mitochondrial membranes as part of a coordinated, reversible suppression of mitochondrial membrane-associated processes, which may include a concomitant reduction in rates of proton pumping and leaking.

Animals↗