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PubMed1988

The effects of adrenocorticotropin hormone and angiotensin II on adrenal corticosteroid secretions in the freshwater turtle Pseudemys scripta.

This study examined the effects of angiotensin II (ANG II) and mammalian adrenocorticotropin hormone (ACTH) on adrenal corticosteroid secretions in the freshwater turtle, Pseudemys scripta. Synthetic turtle ANG II ([Asp1, Val5] ANG II) was infused at rates of 1, 10, and 100 ng/kg/min in conscious turtles while monitoring blood pressure (BP). One 60-min saline (0.6%) infusion preceded the ANG II infusions; two followed. Blood samples were collected at 30- and 60-min intervals and the plasma was frozen at -20 degrees until assay. Mammalian ACTH was infused at doses of 0.1 and 1.0 IU/min; the procedures were followed as delineated above. The plasma was assayed for corticosterone, cortisol, and aldosterone utilizing radioimmunoassay techniques. Infusions of exogenous, native ANG II at subpressor and pressor rates elicited dose-dependent increases in BP, which rose from a control mean of 22.6 +/- 5.8 mm Hg to a maximum mean value of 38.2 +/- 11.0 mm Hg (P less than 0.05 compared to control), and plasma corticosterone concentrations, which rose from a control mean of 6.6 +/- 2.8 ng/ml to a maximum mean value of 27.2 +/- 2.6 ng/ml (P less than 0.05 compared to control). Furthermore, both BP and corticosterone levels returned toward control levels during the final saline recovery period, suggesting that neither physical stress suffered by the animal nor blood volume changes due to infusions and blood sampling affected these parameters. ACTH failed to alter either BP or corticosterone. Neither ANG II nor ACTH had any effect on plasma cortisol or aldosterone concentrations--which fell below the minimal detection levels for these assays.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Cortex↗
PubMed1989

The complete amino acid sequence of growth hormone from the sea turtle (Chelonia mydas).

The complete amino acid sequence of growth hormone (GH) from a reptilian species (the sea turtle, Chelonia mydas) has been determined for the first time. The hormone was reduced, carboxymethylated, and subsequently cleaved in turn with cyanogen bromide and Staphylococcus aureus protease. The intact protein was also cleaved with lysyl endopeptidase and o-iodosobenzoic acid. The resulting fragments were exclusively separated by reversed-phase high-performance liquid chromatography and subjected to sequence analysis by automated gas-phase sequencer employing the Edman method. The sea turtle GH consist of 190 amino acid residues with two disulfide linkages formed between residues 52-160 and 180-188, and possesses a microheterogeneity, indicated by the presence or absence of an additional alanine residue at the N-terminus. Sequence identities of sea turtle GH to other species of GH are 89% with chicken GH, 79% with rat GH, 68% with blue shark GH, 58% with eel GH, 59% with human GH, and 40% with a teleostean GH such as chum salmon. On the basis of amino acid sequence comparisons, a molecular phylogenetic tree is proposed.

Amino Acid Sequence↗
PubMed1989

Salt intake and plasma renin activity in the freshwater turtle.

In mammals, a well-documented inverse relationship exists between oral salt intake and plasma renin activity (PRA). We carried out this study to determine if a similar relationship exists in the freshwater turtle Pseudemys scripta. Three groups of turtles (N = 8 for each group) were fed different amounts of salt dissolved in distilled water (2 cc/kg). The high salt group received 580 mg (10 mEq) NaCl/kg twice per week, the medium salt group received 290 mg (5 mEq) NaCl/kg twice per week, and the low salt (control) group received 2 cc/kg distilled water twice per week with no salt. The animals were weighed weekly and blood was collected by cardiac puncture after 3 and 6 weeks of salt loading and again 3 weeks after termination of the salt loading. PRA and plasma electrolytes (PNa, PK, PCl) were determined. The low salt (control) group showed no changes in any of the measured variables throughout the 9-week study. At 3 weeks the following mean values were obtained for the control group: PNa, 119.5 +/- 7.2 mEq/liter; PK, 5.0 +/- 1.0 mEq/liter; PCl, 74.1 +/- 2.6 mEq/liter; PRA, 1.0 +/- 0.2 ng/ml/hr. In the medium salt group, no significant changes were seen until 3 weeks after termination of the salt loading when PNa and PRA were elevated to 137.9 +/- 3.6 mEq/liter and 1.9 +/- 0.2 ng/ml/hr, respectively (P less than 0.05 compared to control). In the high salt group, PNa (136.5 +/- 6.5 mEq/liter) was elevated after 3 weeks of salt loading. At 6 weeks, PNa (136.8 +/- 4.9 mEq/liter) remained elevated in the high salt group and PCl (86.3 +/- 1.3 mEq/liter) and PRA (1.7 +/- 0.2 ng/ml/hr) also increased significantly (P less than 0.05 compared to control in each case). Three weeks after termination of salt loading, PNa (136.8 +/- 3.3 mEq/liter). PCl (88.0 +/- 1.6 mEq/liter), and PRA (1.9 +/- 0.2 ng/ml/hr) remained elevated (P less than 0.05 in each case) in the high salt group while PK dropped to 3.5 +/- 1.6 mEq/liter (P less than 0.05). The results show that after 6 weeks of salt loading sufficient to raise PNa in the turtle, PRA was significantly elevated.

Animals↗
PubMed1989

Temperature dependence of in vitro pituitary, testis, and thyroid secretion in a turtle, Pseudemys scripta.

In vitro culture was used to examine the direct actions of temperature at the level of pituitary hormone [luteinizing hormone (LH), thyrotropin (TSH), growth hormone (GH), prolactin (PRL)] responses to neuropeptides and two related peripheral endocrine responses [thyroid hormone (T4) and testicular androgen secretion] to pituitary hormones (TSH and gonadotropins) in a turtle, Pseudemys scripta. All these responses were fully suppressed at very low temperatures (5-6 degrees) and maximal near the species' preferred body temperature (28 degrees), but sensitivities differed markedly in intermediate ranges. At the pituitary level, the response of TSH, GH, and PRL to thyrotropin-releasing hormone (TRH) was considerably more temperature sensitive than the response of LH to gonadotropin-releasing hormone (GnRH) stimulation. TSH, GH, and PRL were unresponsive at 20 degrees or below, whereas LH secretion was stimulated almost equally between 12 and 28 degrees; the main effect of cooling on LH secretion was to reduce the duration of the response to GnRH. There was no clear effect of previous thermal history on temperature sensitivity of pituitary neuropeptide responsiveness although the general responsiveness of the gland was altered; however, these latter effects may also be related to variations in other factors such as photoperiod, season, and nutrition. Temperature sensitivities of the thyroid and testes also differed, but in the opposite way from the related pituitary cell types. Thyroid glands were relatively insensitive to temperature and responded to TSH between 12 and 32 degrees, with no difference between 20 and 28 degrees. In contrast, testicular androgen secretion showed an abrupt decline in gonadotropin responsiveness below 28 degrees; dose sensitivity, response rate, and maximal output were affected. Results were similar for sea turtle LH, snapping turtle LH, and ovine follicle-stimulating hormone. Thus, the temperature dependence of the two endocrine systems may have a different rate-limiting component.

Androgens↗
PubMed1989

Seasonal variation in hepatic binding of estrogen in the turtle, Chrysemys picta.

The present study describes the seasonal changes of the estrogen receptor (ER) system in the liver of the turtle, Chrysemys picta. [3H]Estradiol ([3H]E2) binding capacities and affinities of liver cytosols and nuclear extracts were measured with established procedures and analyzed by Scatchard plots. Our data revealed significant seasonal variations in both receptor content and the ER's affinity for [3H]E2 in the liver of the turtle. Nuclear ER content remained at a fairly stable level of 70 fmol/g tissue throughout the year, but exhibited two sharp increases in the months of May and October, attaining values of approximately 150 fmol/g tissue. These rises in nuclear ER content coincided temporally with the two peaks of vitellogenin accumulation and estrogen surge in the annual cycle previously reported for the female turtle. Cytosolic ER level in the liver exhibited a much more complex pattern. It fluctuated with a much wider range of 80 to 250 fmol/g tissue. Right after oviposition in July, it declined to its lowest value of 80 +/- 9 fmol/g tissue but gradually increased to 160 +/- 15 fmol/g tissue in September and remained at this medium range for the remaining of the fall season but rose sharply again to the highest value of the year in December, reaching a value of 270 +/- 7 fmol/g tissue. In the following winter months, cytosolic ER level declined until March before it rebounded to a second peak value of 242 +/- 6 fmol/g tissue in May.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

The complete amino acid sequence of prolactin from the sea turtle (Chelonia mydas).

The complete amino acid sequence of prolactin (PRL) from a reptile, the sea turtle (Chelonia mydas), was determined for the first time. Sequence analysis was performed on fragments obtained from cleavage of intact and performic acid-oxidized hormone with lysyl endopeptidase, Staphylococcus aureus protease, and o-iodosobenzoic acid employing manual Edman degradation. The sea turtle PRL consists of 198 amino acid residues with three disulfide linkages formed between residues 4-11, 58-173, and 190-198 and possesses heterogeneity indicated by four replacements at positions 55, 145, 148, and 171. Sequence comparison with other vertebrate PRLs revealed that the degree of sequence identity conforms well to expectations based on phylogeny except for the rodent PRLs; sea turtle PRL has 86% identity with chicken PRL; 81% with horse, pig, and fin whale PRLs; 75-71% with cattle, sheep, and human PRLs; 60-56% with mouse and rat PRLs; and 35-31% with carp, salmon, and tilapia PRLs.

Amino Acid Sequence↗
PubMed1990

Modulation of neuropeptide-stimulated pituitary hormone secretion in hatchling turtles.

Neuropeptides that have relatively narrow actions on mammalian pituitary secretion may have divergent effects on pituitary hormone secretion in ectothermal vertebrates. In turtles, secretion of both thyrotropin (TSH) and growth hormone (GH) can be stimulated in vitro by thyrotropin-releasing hormone (TRH) and by members of corticotropin-releasing hormone (CRH) and growth hormone-releasing hormone (GHRH) peptide families. To determine if these neuropeptides share common modes of action, and to study other potential regulators of the turtle pituitary, somatostatin-14 (SRIH) and monoamines were tested for direct effects on in vitro basal and neuropeptide-stimulated TSH and GH secretion. Pituitary glands from young turtles (Pseudemys scripta) were cultured in the presence of 25 nM TRH, ovine CRH, or rat GHRH with or without SRIH. Glands were incubated for several 2-hr periods in medium alone or in medium containing peptides. Preincubation for 4 hr with SRIH (6 or 60 nM) significantly reduced basal and TRH-stimulated TSH and GH output (SRIH present during entire incubation). In another experiment, basal hormone secretion was reduced when SRIH (60 nM) was present only during the 2-hr basal period; however, reduction of TSH and GH responses to TRH required the presence of SRIH (60 nM) during the basal period and the period of stimulation. TSH responses to 25 nM oCRH and rGHRH and GH responses to rGHRH were significantly reduced by preincubation with 60 nM SRIH. The biogenic amines, dopamine (DA), serotonin (5HT), and norepinephrine (NE) (50 or 500 nM) were tested for possible direct actions on basal and neuropeptide-stimulated pituitary TSH and GH secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

The effect of anoxic submergence and recovery on circulating levels of catecholamines and corticosterone in the turtle, Chrysemys picta.

The ability of some freshwater turtles to tolerate prolonged anoxia is well known. The role of hormones in the regulation of the metabolic adjustments that occur during anoxia, however, is unknown. This study examined the changes in plasma glucose, lactate, catecholamine, and corticosterone levels during submergence anoxia and recovery at 22 degrees C in the painted turtle, Chrysemys picta. Plasma catecholamine levels increased greatly during anoxia, while corticosterone levels decreased. During recovery from anoxia, plasma catecholamine levels fell rapidly while corticosterone levels increased 10-fold over controls. The results are consistent with a role for the catecholamines and corticosterone in the regulation of glucose metabolism in the turtle during anoxia and recovery, respectively. We hypothesize that the catecholamines function to stimulate hepatic glycogenolysis during anoxia and thereby increase plasma glucose levels. Corticosterone may function in the recovery from anoxia by enhancing the resynthesis of liver glycogen from lactate.

Analysis of Variance↗
PubMed1992

Measurement of plasma thyroxine binding protein in relation to thyroidal condition in the turtle, Trachemys scripta, by radioimmunoassay.

Polyclonal (rabbit) antisera were generated against a high-affinity plasma thyroxine (T4) binding protein (TBP) purified from the turtle, Trachemys scripta, and used to develop a specific radioimmunoassay (RIA). The RIA demonstrated the presence of an immunochemically related protein in the plasma of several other species of Trachemys and in members of several other genera from the same family, Emydidae. Plasma from all nonemydids and some emydid genera either showed no competition or nonparallelism in RIA. The presence and level of radioimmunoassayable TBP in diverse species correlated with results of previous comparative measurements of T4 binding activity. However, an immunoreactive protein of the same molecular weight as TBP was identified in all turtles by Western blot analysis. More detailed studies in T. scripta demonstrated that variations in plasma T4 binding activity induced by experimental or environmental manipulations were related to differences in TBP concentrations. The concentration of TBP varied by orders of magnitude (from less than 1 to ca. 150 mg/liter) in euthyroid animals; levels showed ontogenetic changes (virtually absent in hatchlings) and were directly related to thyroidal status. Experimentally induced hypothyroidism (goitrogen treatment or surgical thyroidectomy) resulted in a marked suppression of TBP, and T4 treatment prevented its decline or reinstated it. Thus, in the turtle, this T4 transport protein may exist in higher concentrations and its levels are more variable and show a different relationship to thyroid activity than the analogous T4 binding globulin (TBG) in mammals.

Aging↗
PubMed1989

Cutaneous fibropapillomas of green turtles (Chelonia mydas).

Six juvenile green turtles (Chelonia mydas) from the Indian River Lagoon System, Florida, U.S.A., with multiple cutaneous fibropapillomas, were kept in isolation and examined over a 6-month period. Histologically, the fibropapillomas consisted of a slightly to moderately hyperplastic epidermis overlying a thickened hypercellular dermis. In the earliest lesions, ballooning degeneration was present predominantly in the stratum basale where rete ridges extended into the dermis; aggregates of mixed inflammatory cells were present around dermal vessels. As the lesions matured, they developed an arborizing, papillary pattern. More mature lesions had a less verrucous, often ulcerated surface, with the dermis composed primarily of large collagenous fascicles and relatively few fibroblasts. While numerous trematode eggs were present within dermal capillaries of a histologically similar biopsy specimen from an Hawaiian green turtle, no trematode eggs were observed in any of 28 biopsies examined from the six Florida green turtles in this study. Low stringency Southern blot hybridization and a reverse Southern blot failed to demonstrate papillomavirus DNA in any of the samples extracted. Ultrastructural evaluation of the earliest lesions demonstrated membrane-bound intracytoplasmic vacuoles within epidermal cells in the stratum basale. Similar vacuoles were also observed in the epidermal intercellular spaces and within the dermis. Occasionally, particles with electron-dense centres and measuring 155 to 190 nm were observed in these vacuoles.

Animals↗
PubMed1987

Characterization of steroid receptors in the gut and kidney of the frog (Rana catesbeiana) and in the gut of the turtle (Chrysemys picta).

Paraglucocorticoid- and paramineralocorticoid-binding cytosolic receptors (pGR, pMR) were demonstrated in the intestine and kidney of the frog, Rana catesbeiana and in the intestine of the turtle, Chrysemys picta, in the presence of sodium molybdate. These receptors were of high affinity and low capacity with the following binding parameters: pGR:Kd:frog intestine (FI), triamcinolone acetonide (TA): 3.3 nM, corticosterone (B): 3.4 nM; frog kidney (FK), TA:4.3 nM, B: 9.3 nM; turtle intestine (TI), TA: 4.8 nM; Nmax: FI, TA: 357, B: 371; FK, TA: 301, B: 157; TI, TA: 350 fmol/mg protein. pMR:Kd: FI, aldosterone: 0.9 and 90 nM (biphasic curves); FK, aldosterone: 0.6 and 36 nM (biphasic curves); Nmax: FI, 13 and 147 fmol/mg protein; FK, 78 and 109 fmol/mg protein. The receptor had the following ligand affinities: pGR: FI and FK: triamcinolone acetonide greater than DOC greater than 11 beta-hydroxyprogesterone greater than progesterone greater than corticosterone greater than cortisol greater than aldosterone greater than 11-dehydrocorticosterone greater than 17 alpha-hydroxyprogesterone greater than cortisone; TI: triamcinolone acetonide greater than corticosterone greater than progesterone greater than DOC greater than cortisol greater than aldosterone; pMR: FI and FK: corticosterone greater than 11 beta-hydroxyprogesterone greater than aldosterone greater than triamcinoline acetonide = cortisol greater than DOC greater than 11-dehydrocorticosterone greater than progesterone greater than 17 alpha-hydroxyprogesterone greater than cortisone. Androgens, estrogens or 18-hydroxycorticosterone did not compete for binding in either tissue. The heat activated frog receptors did not bind to naked DNA, though the turtle receptor did. It was possible to show that cytosol receptor-ligand complexes from all tissues were bound by nuclear acceptor sites. On linear sucrose gradients, the FI TA-receptor complex sediments with a single peak (7.5S), the FK TA-receptor complex gave two peaks (8.0 and 4.4S) and the TI TA-receptor complex showed a single peak (9.0S). The hydrodynamic parameters of the pGR's were determined by gel exclusion on Sephacel S-300. The following results were obtained: Mr: FI, 265, 80, 40 kDa (multiple proteins); FK, 280, 60, 20 kDa (multiple proteins); TI, 366 kDa; Rs: FI, 6.9, 3.9 nm; FK, 6.9, 2.9 nm; TI, 7.6 nm; f/f0: FI, 1.6; FK, 1.6; TI, 1.6. It is suggested on the basis of the binding and hydrodynamic parameters that non-mammalian epithelia corticosterone receptors have undergone biochemical evolution from one class of vertebrates to another.

Aldosterone↗
PubMed1989

Two progesterone receptors in the oviduct of the freshwater turtle Chrysemys picta: possible homology to mammalian and avian progesterone receptor systems.

Two progesterone receptors in the oviduct of the freshwater turtle Chrysemys picta: possible homology to mammalian and avian receptor systems. Here we report the characterization of two specific progesterone receptors in nuclear extracts of the turtle oviduct. The receptors differ in dissociation constants (2.8 nM vs 27 nM) which can be separated on DEAE-Sepharose, the former eluting at 0.08 M KCl and the latter at 0.20 M KCl. [3H]R5020 photoaffinity labeling SDS-PAGE revealed that the 2.8 nM moiety migrates with an apparent molecular weight of 80 +/- 5 kDa and the 27 nM moiety migrates with an apparent molecular weight of 120 +/- 5 kDa. These receptors are termed PR-A and PR-B due to their molecular mass and elution profiles. DNA-cellulose chromatographic studies show that both bind DNA-cellulose with the PR-A eluting at 0.09 M NaCl and PR-B eluting between 0.20-0.21 M NaCl. In reproductively inactive turtles (from the months of January and February) estradiol is undetectable, and PR-B is absent as determined by Scatchard analysis, [3H]R5020 photoaffinity labeling electrophoretic studies and DEAE-Sepharose and DNA-cellulose chromatography. In these animals PR-B can be replenished by estrogen treatment, suggesting a physiological role for both PR-A and PR-B and dependence of PR-B on estradiol.

Animals↗
PubMed1979

Pulmonary receptor chemosensitivity and the ventilatory response to inhaled CO2 in the turtle.

Ventilatory responses of unanesthetized turtles to changes in the intrapulmonary CO2 content of a vascularly isolated and an intact lung were measured during spontaneous breathing. The hyperpnea associated with inhalation of CO2 by the vascularly isolated lung was 19% of that associated with inhalation of CO2 by the intact lung. Transection of the vagus nerve supplying the isolated lung abolished this response. We conclude that both inhibition of pulmonary stretch receptor discharge with increasing levels of FICO2 and a functional increase in central inspiratory volume threshold during hypercapnia contribute to tidal volume increases following CO2 inhalation in normal animals. The major component of the ventilatory response of intact turtles to increasing levels of FICO2, however, was an increase in respiratory frequency. When CO2 was inspired only by the vascularly isolated lung the increase in respiratory frequency was only 21% of that recorded when the same levels of CO2 were inspired by the intact lung. Thus the ventilatory response of turtles to increasing levels of FICO2 is primarily dependent upon concomitant hypercapnia.

Animals↗
PubMed1982

Temperature-induced changes in turtle CSF pH and central control of ventilation.

Cerebrospinal fluid (CSF) and arterial blood acid-base variables, as well as respiratory minute volume (RMV), were measured at three different body temperatures in unanesthetized turtles. RMV remained constant while CSF pH decreased 0.015 U/degrees C with increasing body temperature. These results show that ventilation is not tracking CSF pH when body temperature is the independent variable; however, perfusion of the brain ventricular system of turtles with mock CSF, in which ion-dependent pH decreases were produced, caused large increases in ventilation which were independent of body temperature. Comparisons between turtles and goats reveal that central chemical control of ventilation is functioning similarly in the two animals and appears to fit the alphastat model of ventilatory control proposed by Reeves. These data strongly suggest that both animals are maintaining the fractional dissociation of imidazole constant in central receptive structures, indicating that this system is the model for central chemical control of ventilation in air-breathing vertebrates.

Acid-Base Equilibrium↗
PubMed1982

Resistance of the shell membrane and mineral layer to diffusion of oxygen and water in flexible-shelled eggs of the snapping turtle (Chelydra serpentina).

At oviposition, flexible eggshells of many turtles have an outer mineral layer and an inner membrane layer of approximately equal thickness. We measured conductances of both layers to H2O and O2 at various levels of eggshell hydration. Both the mineral layer of the eggshell and the shell membrane offer significant resistance to diffusion of water vapor and oxygen in eggshells of the snapping turtle, Chelydra serpentina. Conductance to water vapor increases in both the membrane and mineral layer with increasing hydration of the eggshell, but conductance to oxygen decreases under similar conditions. Removal of the mineral layer increases conductance to oxygen in moist and dry eggshells, but decreases conductance at intermediate levels of dehydration. Removal of the mineral layer consistently increases conductance to water vapor. The eggshell membrane accounts for 24-76% of overall resistance to diffusion of water vapor. These results suggest that bulk flow of H2O or physical changes in the shell may interact with diffusion to limit gas exchange through the turtle eggshell.

Animals↗
PubMed1986

Postsynaptic potentials of bulbar respiratory neurons of the turtle.

Membrane potentials of bulbar respiratory neurons of Pseudemys scripta were recorded from unanesthetized, decerebrate animals. Efferent neurograms were recorded from the serratus magnus (inspiratory) and pectoralis (expiratory) nerves. The animals were paralyzed and ventilated by a servo-respirator driven by the pectoralis neurogram to mimic the spontaneous turtle respiratory cycle. Neurons, comparable to mammalian medullary respiratory neurons, were observed, namely: augmenting inspiratory, augmenting expiratory and postinspiratory neurons. In addition, two types of phase-spanning neurons, postinspiratory-expiratory and expiratory-inspiratory, were encountered. The pattern of appearance of inhibitory postsynaptic potentials generally resembled that observed in the cat. The neurons observed correspond to the activity pattern of known respiratory muscles of the turtle. The results suggest that the three phase respiratory cycle of the turtle corresponds to the ternary neural cycle postulated for mammals.

Action Potentials↗
PubMed1989

Oxygen transfer kinetics of red blood cells of the turtle Pseudemys scripta elegans.

The kinetics of O2 uptake into, and release from, the red blood cells (RBC) of the turtle Pseudemys scripta elegans were determined with a stopped-flow technique at varied temperature (10-30 degrees C) and pH (7.5-7.9). The results were compared to those obtained for RBC of other vertebrates and related to morphometric and physiological data on gas/blood diffusion in turtle lungs. The O2 transfer conductance of RBC, G, for O2 release into high concentrations of dithionite, considered to represent the best estimate of true RBC transfer conductance for O2 uptake and release, averaged 0.17 +/- 0.01 at 30 degrees C, 0.13 +/- 0.01 at 20 degrees C, 0.09 +/- 0.01 at 10 degrees C (mean +/- SD, in mmol.min-1.Torr-1.(mlRBC)-1). These values are about one half the corresponding value for human RBC, and this difference may be due to the larger size of turtle RBC (volume, 327 microns 3) compared to human RBC (90 microns 3). The temperature dependence of G, Q10 = 1.3 indicates that, as in human RBC, diffusion through aqueous media is the main limiting factor for O2 exchange. Morphometric data on the lungs of Pseudemys scripta suggest that the resistance to O2 transfer by RBC is lower than that offered by the gas-blood barrier. The total apparent transfer resistance to CO, obtained from previous measurements of pulmonary diffusing capacity for CO in the same species, is much higher than that predicted from the combination of RBC O2 kinetics and morphometric data on gas-blood barrier.

Animals↗
PubMed1984

Turtle and catfish horizontal cells show different dynamic response.

Horizontal cell responses of catfish and turtle have been found to differ in a characteristic way. These characteristics established by white-noise analysis show that the impulse response (first order Wiener kernel) of the catfish horizontal cell has a substantially shorter latency as well as peak response time than that of the turtle. The turtle horizontal cell, on the other hand, has a dynamic gain which is twice that of the catfish. Since these differences were established under conditions of ambient illumination, they may be expected to be functionally important in the visual experience of the animals under normal environmental conditions.

Action Potentials↗