Distribution of glial fibrillary acidic protein-immunopositive structures in the developing brain of the turtle Mauremys leprosa

This study is a continuation of the description of the glial fibrillary acidic protein (GFAP)-immunopositive structures in the adult turtle brain (Kálmán et al. 1994) and presents a comprehensive description of the development of these structures from the 20th embryonic day (E20) to the adult age. GFAP-immunopositive elements were first detected at E28 and by E34 the GFAP-immunopositivity was apparent throughout the brain, except the cerebellum. The appearance of GFAP seemed to be related to the end of cell migration and the formation of the thickened parts of the brain wall, such as the dorsal ventricular ridge. After hatching the pattern of the GFAP-immunopositivity differed from that in the adult only in minute details, except for the brain tracts in which GFAP-pattern was still changing due to myelination, and the molecular layer of the cerebellum in which a transverse fiber system appeared. The GFAP-positive elements belonged originally to the ependymoglia, but later the distortion due to the morphogenetic processes of branching and division changed the pattern almost beyond recognition. In some cases cell bodies--ependymal and non-ependymal--appeared to be GFAP-positive, but no astrocytes (i.e. stellate cells) were detected. The results are discussed in the light of previous observations on developing mammalian, avian and lizard brains.

Abundant synthesis of transthyretin in the brain, but not in the liver, of turtles

The binding of thyroxine to proteins in the blood plasma of the turtle, Trachemys scripta, was analyzed by incubation with radioactive thyroxine, electrophoresis and autoradiography. Albumin and an alpha-globulin were found to bind thyroxine; no thyroxine-binding transthyretin was detected in the prealbumin region. In contrast to blood plasma, a thyroxine-binding prealbumin was observed in medium from T. scripta choroid plexus incubated in vitro. RNA was extracted from brain tissue containing choroid plexus and from liver of T. scripta and Chelydra serpentina and analyzed by hybridization with transthyretin cDNA from the lizard Tiliqua rugosa. The brain RNAs contained substantial amounts of transthyretin mRNA, whereas only trace amounts of transthyretin mRNA were detected in RNA from liver. No transthyretin mRNA was observed in RNA from kidney. The results support the hypothesis that the expression of the transthyretin gene first evolved in the choroid plexus of the brain at the stage of the stem reptiles, whereas abundant transthyretin synthesis in liver evolved much later, and independently, in mammals and birds.

Effects of anoxia on intracellular free Ca2+ in isolated cardiomyocytes from turtles

One of the most important negative consequences of hypoxic stress in the mammalian myocardium is a breakdown in intracellular calcium homeostasis. This study examines the effects of anoxic stress on intracellular calcium regulation in isolated ventricular myocytes from a hypoxia tolerant vertebrate, the western painted turtle (Chrysemys picta bellii). Isolated calcium tolerant cardiomyocytes from turtle hearts were mounted on a glass cover slip that formed the bottom of a sealed, Plexiglas perfusion chamber. Free [Ca2+]i (determined by FURA2 fluorescence) in isolated turtle cardiomyocytes averaged 31.7 +/- 3.2 nM after 30 min of normoxic perfusion (20 degrees C, pHc = 7.77). This value is on the low end of the published range for mammalian cardiomyocytes. Perfusion with anoxic Ringer equilibrated with 3% CO2, resulted in a significant increase in free [Ca2+]i to 941 +/- 494.6 nM after 60 min. Increasing the CO2 in the perfusion solution to 5% or 6% blunted this rise (peak levels after 60 min of anoxia were 420.5 +/- 176.0 nM and 393.8 +/- 132.8 nM, respectively). A further increase to 8% CO2 increased the maximal value for free [Ca2+]i to 610.9 +/- 297.5 nM. In eight cells from the 5% CO2 protocol in which [Ca2+]i was monitored during recovery, reperfusion with normoxic Ringer rapidly lowered intracellular calcium to 92.8 +/- 9.7 nM within 15 min. Anoxia at relatively high extracellular (and hence intracellular) pH results in an increase in free [Ca2+]i comparable in magnitude and time course to that seen in some mammalian cardiomyocyte preparations. Perfusion of anoxic myocytes with Ringer equilibrated with either 5% or 6% CO2 blunted this increase in intracellular calcium, possibly an example of the pH paradox effect. A more severe combination of respiratory acidosis and anoxia (8% CO2) removed this protective effect.

Effect of temperature on oxygen stores during aerobic diving in the freshwater turtle Mauremys caspica leprosa

Oxygen stores available for aerobic diving were studied in the freshwater turtle (Mauremys caspica leprosa) at three constant body temperatures (15 degrees, 25 degrees, and 35 degrees C) and during the thermal transient (30 degrees-15 degrees C) induced by immersion in cold water. The term "aerobic dive limit" has been defined as the maximal duration of the dive before lactate increases. This increase occurs when a critical PO2 value is reached, and it is well characterized at lung level by a sharp increase in the lung apnoeic respiratory quotient. Kinetic analysis of lung gas composition during forced dives at fixed body temperature shows that critical PO2 values rise with temperature and that the postventilatory PO2 at the beginning of a dive decreases, so that the two temperature-dependent factors lead to a significant decrease with temperature in the lung O2 stores available for aerobic diving. During dives with transient body cooling, a natural condition in M. caspica leprosa, temperature equilibration occurs fast enough to expand aerobic scope by bearing the critical PO2 to the same value obtained at a fixed temperature of 15 degrees C. These dives are characterized by reversed CO2 transport (from lung to tissues) and therefore by negative values of the lung respiratory quotient; a decrease in temperature increases CO2 capacitance of tissues, resulting in a fall in PCO2 at constant CO2 content. Because this does not occur in the gas phase, PCO2 difference can lead to diffusion in the direction opposite from normal. This pattern may favour lung-to-tissue O2 transfer, through the Bohr effect. Therefore, the aerobic dive limit is reduced at high temperature not only through a metabolic rate effect but also through a marked decrease in the available O2 stores; fast body cooling (30 degrees-15 degrees C) associated with immersion in cold water extends the O2 stores available for aerobic diving to a level similar to that of immersions at constant body temperatures that are in equilibrium with water temperature.

Decreased total ventricular and mitochondrial protein synthesis during extended anoxia in turtle heart

The turtle heart provides a model system to study the effects of anoxia on protein synthesis without the potentially confounding factor of contractile failure and decreased ATP levels. Protein synthesis, as measured by 3H-labeled phenylalanine incorporation, was studied under conditions of normoxia and anoxia in isolated perfused turtle [Trachemys (= Pseudemys) scripta elegans] hearts at 15 degrees C. Heart rate, cardiac output, and ventricular pressure development were unaffected by 2 or 3 h of anoxia. Despite the anoxia, energy levels in the heart were presumably still high, since contractility was maintained. RNA content of ventricle decreased after anoxic perfusion. Rates of total protein synthesis rates in ventricle were threefold lower under anoxia than under normoxia. These findings suggest that the total level of RNA is one determinant of protein synthesis. Incorporation of label into protein extracted from mitochondria was also assessed. The ratio of mitochondrial to whole ventricular protein synthesis was significantly lower after anoxia, revealing preferential control mechanisms under anoxia between the synthesis of total cellular protein and protein destined for mitochondria. Isolated mitochondria were still coupled after 2 or 3 h of anoxia. In effect, the mitochondria enter into a state of hypometabolism in terms of rates of ATP synthesis and protein synthesis, but functional integrity is maintained. The decrease in protein synthesis in general and mitochondrial protein synthesis in particular may represent an adaptation to allow the partitioning of the available energy resources toward mechanical function during anoxia.

Liver protein kinase C isozymes: properties and enzyme role in a vertebrate facultative anaerobe

Protein kinase C was purified to homogeneity from liver of the anoxia-tolerant turtle (Trachemys scripta elegans). Two isozymes were present and were identified as PKC alpha and PKC beta by hydroxylapatite chromatography and cross-reaction with specific antibodies to the mammalian isozymes. Kinetic characterization of the isozymes showed that both required phospholipids and Ca2+ for activation and both were inhibited by low concentrations of PKC inhibitors. The PKC alpha was activated more strongly by phosphatidylinositol and lysophosphatidylinositol compared with PKC beta. Treatment with trypsin did not activate turtle PKC isozymes, but generated inactive PKC beta, whereas PKC alpha was resistant to inactivation. Anoxia exposure of turtles in vivo, via submergence in N2-gassed water at 7 degrees C, altered the activity and subcellular distribution of PKC in liver. After 1 hr of anoxic exposure at 7 degrees C, the activity of membrane-bound PKC had increased by 2.4-fold and represented a translocation of 40% of PKC beta and more than 80% of PKC alpha from the cytosol to the membrane-associated fraction. With longer submergence, however, membrane-bound PKC activity was suppressed again. This two-phase response to anoxia by PKC suggests that an activation of PKC, through its translocation to the membrane, is important in mediating the initial metabolic responses to submergence, which include an activation of glycogenolysis during the hypoxia transition period. With sustained anoxia exposure, the subsequent reduction of PKC activity may be part of the overall mechanism of metabolic rate depression that allows endurance of prolonged anoxia.

Temporal and geographic variation of organochlorine residues in eggs of the common snapping turtle (Chelydra serpentina serpentina) (1981-1991) and comparisons to trends in the herring gull (Larus argentatus) in the Great Lakes basin in Ontario, Canada

Common snapping turtle (Chelydra serpentina serpentina) eggs from five sites within the Great Lakes basin, and from a reference site in north-central Ontario were collected during 1981-1991 and analyzed for four organochlorine pesticides, polychlorinated biphenyls (PCBs) including six non-ortho PCBs, polychlorinated dibenzodioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs). The pattern of geographic variation was consistent over time in eggs with Cootes Paradise/ Hamilton Harbour and Lynde Creek eggs on Lake Ontario containing the highest concentrations and most PCDD and PCDF congeners among all sites. Eggs from Cranberry Marsh on Lake Ontario contained organochlorine concentrations similar to those from Big Creek Marsh and Rondeau Provincial Park on Lake Erie except PCDDs and PCDFs which occurred at higher concentrations and more congeners were detectable in Cranberry Marsh eggs. Concentrations of most contaminants in turtle eggs from Algonquin Park, the reference site, have significantly decreased in the past decade. Dieldrin concentrations, however, increased in Algonquin Park eggs from 1981 to 1989. Significant decreases in concentrations of hexachlorobenzene, mirex and PCBs occurred between turtle eggs collected in 1981/84 and 1989 at Big Creek Marsh and Rondeau Provincial Park, whereas there was no significant change in concentrations of p,p'-DDE and dieldrin. In Lake Ontario eggs, concentrations of PCBs, p,p'-DDE and dieldrin increased significantly between 1984 and 1991. Differences were also found in patterns of temporal variation in contamination between herring gulls (Larus argentatus) and snapping turtles which were attributed to differences in diet. Elevated and continued contamination in turtle eggs from Lake. Ontario is probably due to a combination of local sources of chemicals and consumption of large migratory fish that spawn in wetlands inhabited by these turtles.

Cardiac force and high-energy phosphates under metabolic inhibition in four ectothermic vertebrates

Isometric twitch tension of ventricular preparations stimulated at 0.2 Hz fell over 30 min of anoxia by a fraction decreasing in the order rainbow trout, cod, eel, and freshwater turtle. Drops in the estimated cytoplasmic energy state were related to larger tension losses for trout than for the other species, possibly due to larger changes in free phosphate. Anoxic energy degradation was slower for turtle than for the other species. Anoxia combined with glycolytic inhibition (1 mmol/l iodoacetate) enhanced the decrease in twitch tension for a drop in energy state and enlarged the increase in ADP/ATP relative to that in creatine/phosphocreatine to an extent inversely related to the creatine kinase activity. Furthermore, it increased resting tension to an extent possibly related to myosin-adenosinetriphosphatase (ATPase) activity and lowered the content of phosphorylated adenylates in trout and turtle myocardium. The results indicate that species differences in performance of the metabolically challenged myocardium depend on energy-degrading processes, e.g., myosin-ATPase activity, phosphate release, creatine kinase activity, and efflux/degradation of ADP and AMP, and that glycolysis offers protection due to its cytoplasmic localization.

Specific binding sites for atrial natriuretic peptide in the freshwater turtle, Amyda japonica

Specific binding sites for atrial natriuretic peptide (ANP) were investigated by in vitro autoradiographic techniques in various tissues of the freshwater turtle, Amyda japonica. A high density of binding sites for 200 pM of 125I-labelled rANP(1-28) was located in the glomeruli of the kidney and the cortical portion of the adrenal gland. A moderate density of binding sites was seen in the arachnoid matter and choroid plexus of the third and lateral ventricles of the brain and the epididymis. A low density of binding sites was revealed in lamina propria of the mucosa of stomach and intestine, the seminiferous tubules of testes, and the epithelial layer of oviduct. In the presence of excess unlabelled rANP(1-28) (1 microM), binding to these structures were completely displaced. Therefore, specific ANP receptors exist in the kidney, adrenal gland, stomach, intestine, oviduct, epididymis, seminiferous tubules and brain. The ANP system may be involved in physiological regulatory function in the freshwater turtle, Amyda japonica.

[Growth, food conversion and mortality in Eretmochelys imbricata (Reptilia: Chelonidae) in artificial ponds in Costa Rica]

Growth rates, feed conversion and mortality of cultured Eretmochelys imbricata (hawksbill turtle) were studied in concrete raceways by feeding with fresh fish meal (tilapia) and in duplicate (tanks of 21 m2). The turtles were 11 months old at the beginning of the experiment, with and average caparace straight length of 23.64 +/- 1.94 cm, an average caparace curved length of 24.15 +/- 1.94 cm and an average weight of 1527 +/- 2.54 g. The experiment was carried out during six months and a density of 3 ind/m2 was used. The equation of Von Bertalanffy for the growth of E. imbricata was LRC = 3.5 + [(82.0 -3.5) (1-e-0.67432 (t))]. The relationship between caparace straight length-weight was W = 5.207 x 10(-3) LRC 3.8807 (r = 0.99). The feed conversion was 1.54 +/- 0.74 and the mortality was zero during the study.

Lactate distribution and metabolism during and after anoxia in the turtle, Chrysemys picta bellii

To determine the fate of lactate during and after prolonged anoxia, 14C-labeled lactate was injected into turtles after 2 h of a 6-h submergence at 20 degrees C. 14C activities of plasma and chamber water were tested at intervals during anoxia and also in expired air during 39 h of recovery. Partitioning of label in major body compartments [extracellular fluid (ECF), intracellular fluid (ICF), and shell] and 14C activity and glycogen in selected tissues (heart, liver, and muscle) were measured after anoxia (n = 7) and after recovery (n = 6). Shell 14C and [lactate] were extensively measured on six anoxic turtles. During anoxia all 14C remained in the animal indicating no urine production. At 6 h of anoxia 47% of recovered 14C, presumably still as lactate, was in the ECF, 27% in the ICF, and 30% in the shell. During recovery, plasma [lactate] fell from 35 to 5 meq, but surrounding water and expired air accounted for only 9 and 8%, respectively, of recovered label. The ICF portion grew to 41%, associated with a recovery in tissue glycogen. The shell still had 22% of total label. We conclude that, during recovery from anoxia, lactate is predominantly resynthesized to glycogen, and only a small fraction is directly oxidized. During anoxia, however, lactate is widely distributed in the body, and a surprisingly large and functionally significant fraction resides in the shell.

Purification and characterization of turtle pepsinogen and pepsin

Pepsinogen was purified from the gastric mucosa of soft-shelled turtle (Trionyx sinensis) by a series of chromatographies on DEAE-cellulose, Sephadex G-100, and Q-Sepharose. Upon chromatography on Q-Sepharose, it was separated into nine isoforms. These isoforms showed a relative molecular mass of approximately 43,000 Da on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and isoforms 4 through 9 contained carbohydrate (approx. 2% each). Insofar as they were examined, their NH2-terminal sequences differed only in showing substitution at a few positions. At pH 2.0, they were rapidly activated to the corresponding isoforms of pepsin in a stepwise manner. The nine isoforms showed similar specific activity toward hemoglobin and hydrolyzed N-acetyl-L-phenylalanyl-L-diiodotyrosine, a good substrate for pepsin A, at somewhat different rates. They were inhibited by pepstatin to various extents, more strongly than human pepsin C but less strongly than human pepsin A. All isoforms appeared to have similar cleavage specificity toward oxidized insulin B chain, which resembled those of both human pepsins A and C. A cDNA clone for one of the zymogen isoforms was isolated and sequenced. The amino acid sequence thus deduced was more homologous with those of mammalian pepsinogens A than those of mammalian pepsinogens C or prochymosin.

Positive feedback by a potassium-selective inward rectifier enhances tuning in vertebrate hair cells

Electrical resonance in vertebrate hair cells shapes receptor potentials and tunes each cell to a narrow band of frequencies. We have investigated the contribution of a potassium-selective inward rectifier (IR) to electrical resonance, isolating outward current carried by IR from other ionic currents active in the physiological voltage range (-75 to -30 mV) using a combination of potassium and calcium channel antagonists. IR expression is tightly regulated in the turtle's auditory epithelium, as revealed by the observation that its size declines systematically with resonant frequency. A critical feature of IR is the rapid inhibition produced by depolarization, which results in a negative slope in the steady-state current-voltage relation in the vicinity of the resting potential (-50 mV). The increasing block of outward current produced by depolarization is functionally equivalent to activating an inward current, suggesting that IR provides positive feedback and, in hair cells, serves an electrical function ordinarily reserved for voltage-dependent sodium and calcium currents. Additional support for this idea comes from the observation that superfusion with cesium selectively reduces IR and eliminates resonance in cells tuned to low frequencies and degrades resonant quality in cells tuned to more than 50 Hz.

Burst-generating neurones in the dorsal horn in an in vitro preparation of the turtle spinal cord

1. In transverse slices of the spinal cord of the turtle, intracellular recordings were used to characterize and analyse the responses to injected current and activation of primary afferents in dorsal horn neurones. 2. A subpopulation of neurones, with cell bodies located centrally in the dorsal horn, was distinguished by the ability to generate a burst response following a hyperpolarization from rest or during a depolarization from a hyperpolarized holding potential. The burst response was inactivated at the resting membrane potential. 3. The burst response was mediated by a low threshold Ca2+ spike assumed to be mediated by T-type Ca2+ channels since it resisted tetrodotoxin and was blocked by 3 mM Co2+ or 100-300 microM Ni2+ and resembled the low threshold spike (LTS) described elsewhere. 4. Some burst-generating cells also displayed plateau potentials mediated by L-type Ca2+ channels. In these cells the burst following a hyperpolarizing current pulse, applied from the resting membrane potential, facilitated the activation of the plateau potential. Wind-up of the plateau potential was produced when the hyperpolarizing pulse generating the burst was repeated at 0.1-0.3 Hz or faster. 5. The burst response and the underlying low threshold Ca2+ spike were activated synaptically by primary afferent stimuli in a voltage range hyperpolarized from the resting membrane potential. 6. Cells with bursts were morphologically distinguishable from cells with bursts and plateau properties. 7. Our findings in this and the preceding paper show that the intrinsic response properties of particular subtypes of neurones in the dorsal horn have a profound influence on the amplitude and time course of the responses mediated by primary afferent fibres. We predict that these postsynaptic properties are probable targets for synaptic modulation.

Plateau-generating neurones in the dorsal horn in an in vitro preparation of the turtle spinal cord

1. In transverse slices of the spinal cord of the turtle, intracellular recordings were used to characterize and analyse the responses to injected current and activation of primary afferents in dorsal horn neurones. 2. A subpopulation of neurones, with cell bodies located laterally in the deep dorsal horn and dendrites radiating towards the pial surface, was distinguished by the ability to generate plateau potentials. Activation of the plateau potential by a suprathreshold depolarizing current pulse produced an increasing firing frequency during the first few seconds and a sustained after-discharge. 3. The plateau potential was assumed to be mediated by L-type Ca2+ channels since it was blocked by Co2+ (3 mM) and nifedipine (10 microM) and enhanced by Bay K 8644 (0.5-2 microM). 4. The threshold for activating the plateau potential declined during the first few seconds of depolarization. The decline in threshold gradually subsided over 3-10 s after repolarization. 5. Frequency potentiation of the plateau potential contributed to wind-up of the response to depolarizing current pulses and primary afferent stimuli repeated at frequencies higher than 0.1-0.3 Hz. 6. The sustained after-discharge mediated by the plateau potential was curtailed by a slow after-hyperpolarization (sAHP) evoked by strong depolarizations. The relative strength of the plateau potential and sAHP varied among cells. In some cells the plateau potential and sAHP interacted to produce damped oscillations upon depolarization. The sAHP was mediated by both apamin and tetraethylammonium (TEA)-sensitive K+ channels. 7. Our findings suggest that basic properties of sensory integration may reside with the specialized intrinsic response properties of particular subtypes of neurones in the dorsal horn.

Water compartmentalization and extracellular tortuosity after osmotic changes in cerebellum of Trachemys scripta

1. Water compartmentalization in the turtle cerebellum subject to media of different osmolalities was quantified by combining extracellular diffusion analysis with wet weight and dry weight measurements. The diffusion analysis also determined the tortuosity of the extracellular space. 2. Isolated cerebella were immersed in normal, oxygenated physiological saline (302 mosmol kg-1), hypotonic saline (238 mosmol kg-1) and a series of hypertonic salines (up to 668 mosmol kg-1). The osmolality was varied by altering the NaCl content. 3. Extracellular volume fraction and tortuosity of the granular layer of the cerebellum were determined from measurements of ionophoretically induced diffusion profiles of tetramethylammonium, using ion-selective microelectrodes. The volume fraction was 0.22 in normal saline, 0.12 in hypotonic medium and 0.60 in the most hypertonic medium. Tortuosity was 1.70 in the normal saline, 1.79 in the hypotonic and 1.50 in the most hypertonic saline. 4. The water content, defined as (wet weight-dry weight)/wet weight, of a typical isolated cerebellum (including granular, Purkinje cell and molecular layers) was 82.9%. It increased to 85.2% in hypotonic saline and decreased to 80.1% in the most hypertonic saline. 5. Measurements of extracellular volume fraction and water content were combined to show that hypotonic solutions caused water to move from the extracellular to the intracellular compartment while hypertonic solutions caused water to move from the intracellular to extracellular compartment, with only a relatively small changes in total water in both cases. 6. These results suggest the use of the isolated turtle cerebellum as a model system for studying light scattering or diffusion-weighted magnetic resonance imaging.

Adenylyl cyclase activity in turtle vomeronasal and olfactory epithelium

Many vertebrates have two olfactory systems such as the main olfactory organ and the vomeronasal organ. To compare the transduction mechanism in both systems, we measured adenylyl cyclase activity in turtle vomeronasal and olfactory epithelium preparations. Whereas forskolin and GTP induced cAMP accumulation in vomeronasal preparations, common odorants, which induced cAMP accumulation in olfactory preparations and electrophysiological responses in vomeronasal organs, did not induce cAMP accumulation in vomeronasal preparations. The present results suggest that the cAMP-mediated transduction pathway in the vomeronasal organ is not involved in transduction for common odorants and probably plays a role in perception of specific chemosignals.

Biochemistry below 0 degrees C: nature's frozen vertebrates

Although alien to man, the ability to endure the freezing of extracellular body fluids during the winter has developed in several species of terrestrially hibernating frogs and turtles as well as in many species of insects and other invertebrates. Wood frogs, for example, can endure freezing for at least 2 weeks with no breathing, no heart beat or blood circulation, and with up to 65% of their total body water as ice. Our studies are providing a comprehensive view of the requirements for natural freezing survival and of the physical and metabolic protection that must be offered for effective cryopreservation of vertebrate organs. Molecular mechanisms of natural freeze tolerance in lower vertebrates include: 1) control over ice crystal growth in plasma by ice nucleating proteins, 2) the accumulation of low molecular weight cryoprotectants to minimize intracellular dehydration and stabilize macromolecular components, and 3) good ischemia tolerance by all organs that may include metabolic arrest mechanisms to reduce organ energy requirements while frozen. Cryomicroscopy of tissue slices and magnetic resonance imaging (MRI) of whole animals is revealing the natural mode of ice propagation through an organism. MRI has also revealed that thawing is non-uniform; core organs (with high cryoprotectant levels) melt first, facilitating the early resumption of heart beat and blood circulation. Studies of the production and actions of the natural cryoprotectant, glucose, in frogs have shown its importance in maintaining a critical minimum cell volume in frozen organs and new work on the metabolic effects of whole body dehydration in 3 species of frogs has indicated that adaptations supporting freeze tolerance grew out of mechanisms that deal with desiccation resistance in amphibians. Studies of the regulation of cryoprotectant glucose synthesis by wood frog liver have shown the role of protein kinases and of alpha and beta adrenergic receptors in regulating the glycemic response, and of changes in membrane glucose transporter proteins to facilitate cryoprotectant distribution.

Multicatalytic proteinase activity in turtle liver: responses to anoxia stress and recovery

Activities of the multicatalytic proteinase complex (MPC) were detected in turtle (Trachemys scripta elegans) liver. The ratio of peptidylglutamyl-peptide bond hydrolyzing, trypsin-like, and chymotrypsin-like activities was 6:2.7:1 for the MPC partially purified by Sepharose CL-6B gel filtration. Molecular mass of the turtle liver enzyme was 940 +/- 46 kD. Nondenaturing PAGE revealed a single band containing MPC activity reacting with peptide substrate. In vivo anoxia exposure (20 h submergence in N2-bubbled water) and subsequent 24 h aerobic recovery stimulated changes in liver protease activity. Peptidylglutamyl-peptide bond hydrolyzing activity of the partially purified MPC increased by 29% during aerobic recovery. Elevated MPC activity during recovery may serve to catabolize specific stress-related proteins or to remove proteins damaged by oxygen free radicals generated upon the reintroduction of oxygen.

Localization of 2-[125I]iodomelatonin binding sites in visual areas of the turtle brain

The hormone melatonin is believed to play an important role in the regulation of both circadian and circannual rhythms. In mammalian vertebrates melatonin receptors are discretely localized, with broader distributions reported in avians and reptiles. To examine the sites at which melatonin may act in the turtle brain, 2-[125I]iodomelatonin binding sites were assessed using quantitative autoradiography. Specific binding sites were primarily restricted to forebrain structures with a wide distribution in visual recipient areas. The distribution of melatonin sensitive sites within the turtle visual system suggests that the ability to transduce received photoperiodic signals in the reptilian brain is broadly distributed within the central nervous system.

Characterization of the disulfide bonds and the N-glycosylation sites in the glycoprotein from Rathke's gland secretions of Kemp's ridley sea turtle (Lepidochelys kempi)

The disulfide bonds and N-glycosylation sites in a glycoprotein from the Rathke's gland secretion of the Kemp's ridley turtle (Lepidochelys kempi) have been characterized with respect to peptide sequences and glycan structures. The glycoprotein constitutes about 70% of the total protein in the secretion, and based on partial sequence information, it shows more than 20% identity with both the catalytic (esterases) and the noncatalytic (thyroglobulin) members of the esterase/lipase family of proteins. For the determination of the disulfide locations, the glycoprotein was digested with chymotrypsin, and the three HPLC peptide peaks yielding fluorescent products after treatment with tributylphosphine (Bu3P) and 4-(aminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (ABD-F) were collected. The three fractions were treated with the same reagents in separate experiments, the resulting pairs of ABD-Cys-containing peptides were separated by HPLC, and the sequence of each individual peptide was determined. The peptide identity established that three disulfide bonds existed in the glycoprotein: Cys 65-Cys 91, Cys 254-Cys 265, and Cys 130-Cys 404; the first two of these are conserved in all the members of the esterase family. For the study of the glycosylation sites, the glycoprotein was reduced with Bu3P and the SH groups covalently blocked with ABD-F, and the resulting product was digested with chymotrypsin. The glycopeptides were isolated by affinity chromatography, separated by reverse-phase HPLC, and subjected to sequence analysis and fast atom bombardment mass spectrometry before and after separation of the glycans and the peptides through the action of glycoamidase. Three separate glycosylation sites were identified, each containing multiple glycans. The sugar analyses of the hydrolysates of the glycoprotein indicated that only GlcNAc and Man were present as building blocks, and the mass spectrometric data showed that Man3GlcNAc2-, GlcNAc2-4Man3GlcNAc2-, and possibly GlcNAc2Man2GlcNAc2- were the major glycan structures, distributed differently at the three sites. The three glycosylation sites match three of the nine sites glycosylated in human serum choline esterase, and one of them, Asn 106, is also found as one of two glycosylation sites in the homologous segment of thyroglobulin.

Metabolic adaptations supporting anoxia tolerance in reptiles: recent advances

Animal survival during severe hypoxia and/or anoxia is enhanced by a variety of biochemical adaptations including adaptations of fermentative pathways of energy production and, most importantly, the ability to sharply reduce metabolic rate by 5-20 fold and enter a hypometabolic state. The biochemical regulation of metabolic arrest is proving to have common molecular principles that extend across phylogenetic lines and that are conserved in different types of arrested states (not only anaerobiosis but also estivation, hibernation, etc.). Our new studies with anoxia-tolerant vertebrates have identified a variety of regulatory mechanisms involved in both metabolic rate depression and in the aerobic recovery process using as models the freshwater turtle Trachemys scripta elegans and garter snakes Thamnophis sirtalis parietalis. Mechanisms include: 1) post-translational modification of cellular and functional proteins by reversible phosphorylation and changes in protein kinase (PKA, PKC) and/or phosphatase activities to regulate this, 2) reversible enzyme binding associations with subcellular structural elements, 3) differential gene expression and/or mRNA translation producing new mRNA variants and new protein products, 4) changes in protease activity, particularly the multicatalytic proteinase complex, and 5) both constitutive and anoxia-induced modifications to cellular antioxidant systems to deal with oxidative stress during the anoxic-aerobic transition of recovery.

Radioligand and immunochemical studies of turtle oviduct progesterone and estrogen receptors: correlations with hormone treatment and oviduct contractility

Progesterone (PR) and estrogen (ER) receptors were previously identified and characterized in the reproductive tract of the turtle, Chrysemys picta, and changes in PR levels were monitored during the seasonal cycle. To understand the hormonal regulation of PR, intact and ovariectomized animals were treated with estradiol, progesterone, and a combination of estradiol and progesterone, and high affinity PR and ER levels were determined by radioligand binding studies. Ovariectomy significantly decreased ER levels; in contrast, PR levels increased following ovariectomy. In both intact and ovariectomized animals, estradiol alone did not elevate PR levels above control; however, the PR was down-regulated by progesterone. ER levels in ovariectomized animals were not restored by any of the steroid regimens. By Western blot analysis, PR levels appeared to increase following ovariectomy, were unaffected by estradiol, and were somewhat decreased following progesterone treatment in estradiol-primed ovariectomized animals. While not quantitative, these results are supportive of radioligand binding studies. Immunocytochemical studies of oviduct PR followed the same pattern showing increased immunoreactivity following ovariectomy, no change with estradiol, and a decrease following progesterone treatment of estradiol-primed animals. Oviduct contractility was monitored as a physiological index of progesterone action. Estradiol significantly increased the amplitude of the contractions both in vivo and in vitro, whereas progesterone in combination with estradiol significantly inhibited the estrogen effect. This study suggests that estradiol alone may not be adequate for regulation of both ER and PR. While progesterone down-regulates its own receptor, it does not appear to influence the ER. These data are in contrast to mammalian and avian studies which show that estradiol increases both the ER and PR in the reproductive tract, and progesterone down-regulates both receptors.