Model studies of intracellular acid-base temperature responses in ectotherms

Measurements of intracellular pH (pHi) in air-breathing ectotherms have only been made in the steady state; these pHi indicate that protein charge state, measured as alpha imidazole (alphaIM), the fractional dissociation of protein histidine imidazole groups, is preserved when ectotherm tissues change temperature in vivo, with related changes in pHi and PCO2. In partial answer to the question of how such tissues are able to avoid disrupting transients to functions sensitive to protein charge states, model studies were carried out to assess the passive intracellular buffer system response to a combined change in body temperature and CO2 partial pressure as occurs in vivo in these species. The cell compartment was modeled as a closed volume of ternary buffer solution, containing protein imidazole (50 mM/1); phosphate (15 mM/1) and CO2-bicarbonate buffer components, permeable only to CO2 and permitted no change in buffer base. Excursions from a steady-state non-equilibrium pHi were computed to a step-change in temperature/PCO2. Computations for frog (Rana catesbeiana) striated muscle show that the calculated pHi response on the basis of estimated composition and concentration of cell buffer components, moves along the curve describing the steady-state temperature relationship. No transient away from steady-state alphaIM and carbon dioxide content need be postulated. Applications to turtle (Pseudemys scripta) striated muscle are also explored. These calculations show that ectotherm cells may be capable of responding without appreciable time for adaptation to intracellular acid-base state changes incurred by sudden alteration of body temperature in vivo, given the observed adjustments of blood PCO2 with temperature.

Active transport of sugars in tortoise intestine

The tortoise intestine capability for active transport of sugars has been studied in vitro at 30 degrees C, using labelled sugars. A release of glucose from the glycogen stores of the intestinal wall to the medium took place throughout the incubation period of the sacs. An active transport of 14C-D-glucose against a concentration gradient from the mucosal to the serosal compartment was evident, whereas no such activity could be detected for 14C-D-galactose. The tissue oxygen uptake was 36% higher with glucose than with galactose in the medium.

Plasma amino acids in reptiles after feeding protein or amino acids and after injecting amino acids

Turtles (Pseudemys scripta elegans) and alligators (Alligator mississipiensis) were fed fish, casein, or free amino acid mixtures, or were injected with free amino acid mixtures, quantities in each case being equivalent to about 42 mmoles of amino acids/kg body weight. The experiments were designed to determine whether protein synthesis normally precedes catabolism of the amino acids absorbed from digesting food. Both animals disposed of free or food-derived amino acids more rapidly than could be accounted for by catabolism alone, but the transient increases in turtle plasma concentrations consisted mostly of essential amino acids, whereas the alligator plasma showed little increase in essential amino acids and considerable rises in four nonessential amino acids, glutamine, glutamic acid, glycine and alanine. Despite some species variation, these two species with low metabolic rates apparently utilized protein synthesis to dispose of amino acid mixtures prior to the necessarily slow process of catabolism for energy.

H+ current response to CO2 and carbonic anhydrase inhibition in turtle bladder

To evaluate the role of CO2 and carbonic anhydrase (CA) in H+ transport (JH) by turtle urinary bladder the effect of CO2 addition, with and without addition of CA inhibitiors, was examined on JH. Since in the presence of exogenous CO2 and HCO3- the pH stat-measured rate of mucosal (M) acidification underestimates JH by the rate of electroneutral HCO3- secretion, the reverse short-circuit current (RSCC) applied across ouabain-treated bladders was used to estimate JH. That the RSCC is a measure of JH was demonstrated by: 1) in the absence of added CO2 and HCO3- the rate of M acidification totally accounted for the RSCC, and 2) increases in RSCC with CO2 addition occurred without changes in Na+ and K+ fluxes or the coupled ration of HCO3- secretion for Cl-absorption. When serosal (S) percent CO2 was progressively progressively increased JH achieved a maximum rate of 64 +/- 3 muA (SE) with 4.5% CO2. At higher S percent CO2 JH did not change, suggesting that factors other than the rate of CO2 hydration were rate limiting. The maximum rate of JH was not decreased by low concentrations of CA inhibitors (acetazolamide, 5 X 10(-5) M), although the percent CO2 at which this maximum rate occurred increased to 8.5%. The increased percent CO2 requirement for the maximum rate of JH with low concentrations of CA inhibitors suggests that these agents alter JH by decreasing the rate of enzymatic CO2 hydration. At high concentrations (acetazolamide, 5 X 10(-4) M) these inhibitors decrease the maximum rate of JH in the presence of CO2, implying that these inhibitors at higher concentrations directly interfere with the H+ transport system.

Heavy metal-induced alterations in ion transport by turtle urinary bladder

Previous studies of heavy metal salt-induced acute renal failure demonstrated abnormalities of fluid and solute transport by nephron segments and alterations in glomerular filtration rate and renal hemodynamics. To determine the direct effects of uranyl nitrate (UN) or HgCl2 on ion transport, their effects were studied on the isolated urinary bladder of the turtle. Unidirectional 24Na+ and 36Cl- fluxes were measured across short-circuited bladders. The addition of 0.1 mM UN to the mucosal solution resulted in a 69.9 +/- 4% (SEM) decrease in short-circuit current (SCC) without change in transepithelial resistance. Net Na+ flux (7.95 +/- 0.81 mueq/h per 8 cm2) decreased by the same magnitude as the SCC, primarily due to a 5.75 +/- 0.76 mueq/h per 8 cm2 decrease in the mucosal- (M) to-serosal (S) Na+ flux. Net Cl- flux decreased also primarily due to a decrease in M-to-S Cl- flux. Addition of 0.4 mM UN to S did not measurably affect the SCC or ion fluxes. The addition of 10 muM HgCl2 in another group of bladders reduced SCC and M-to-S Na+ flux by 81 +/- 7% without change in Cl- fluxes or resistance. The removal of either UN or HgCl2 from M by washing did not reverse the decreased SCC, but after washing addition of either dithiothreitol, 2 mM, or amphotericin B, 20 mug/ml, to M completely reversed the effects of UN or HgCl2 on SCC. These studies suggest that heavy metal salts inhibit Na+ transport by the turtle bladder without altering passive ion fluxes.

Isolation and characterization of follicle-stimulating hormone and luteinizing hormone and its subunits from snapping turtle (Chelydra serpentina) pituitaries

Highly purified luteinizing hormone and follicle-stimulating hormone have been isolated from extracts of snapping turtle (Chelydra serpentina) pituitaries. Both hormones are potent in non-mammalian gonadotropin bioassays (1.8 X NIH-LH-S1 and 30 X NIH-FSH-S1). The materials have been characterized by polyacrylamide gel electrophoresis, amino terminal group analysis, amino acid and carbohydrate content, and, in the case of turtle luteinizing hormone, ultracentrifugation. The luteinizing hormone was shown to dissociate and subunits were prepared by the countercurrent distribution technique and characterized. Biological activity of the hormone could be regenerated by recombination of the subunits. In addition, it was shown that the snapping turtle luteinizing hormone subunits could be combined with subunits from ovine luteinizing hormone with generation of significant biological activity. Comparisons in properties of the turtle gonadotropins have been made with ovine gonadotropins, showing, in many cases, similarities in properties, suggesting structural features which have been conserved during evolution.

Energetics of swimming of a sea turtle

Young (mean mass 735 g) green turtles (Chelonia mydas) were able to swim in a water channel at sustained speeds between 0–14 and 0–35 m.s-1. Oxygen consumption at rest was was 0–07 l.kg-1.h-1; at maximum swimming speed oxygen consumption was 3–4 times greater than at rest for a given individual. In comparison with other animals of the same body mass the cost of transport for the green turtle (0.186lO2.kg-1.km-1) is less than that for flying birds but greater than that for fish. From drag measurements it was calculated that the aerobic efficiency of swimming was between 1 and 10%; the higher efficiencies were found at the higher swimming speeds. Based upon the drag calculations for young turtles, it is estimated that adult turtles making the round-trip breeding migration between Brazil and Ascension Island (4800 km) would require the equivalent of about 21% of their body mass in fat stores to account for the energetic cost of swimming.

The sulfatides and some histochemical correlations of the lachrymal glands involved in salt secretion in Chelonia

High concentrations of sulfolipids (four fractions having different hexose/sulfate ratio), intense enzyme activity (ATPase, oxoreductases) and evidence of mucines (staining with PAS and Alcian blue) in intercellular spaces were found in the lachrymal glands of Caretta caretta and Malaclemys terrapin adapted to sea water. In addition, the supranuclear region of the gland cells in Malaclemys terrapin is filled with mucin granules. These biochemical and histochemical observations indicate that these glands have a function in salt secretion in both species and are also consistent with a function of mucous secretion exclusively in Malaclemys terrapin. Limited signs of hypotrophy are not accompanied by changes in concentrations of sulfolipids in Malaclemys terrapin adapted to fresh water; only the reactions for enzyme activities are less intense. The mucous secretion is not affected, whereas, in correlation with changes in salt secretion, the change in ATPase activity is mot conspicuous. The correlations between the different components of the gland and salt secretion are compared with salt glands of birds and elasmobranchs.

The blood-aqueous barrier in five species

The in vivo sites of the blood-aqueous barrier were determined in five animal species, using acriflavine neutral (224 mol. wt.), ultrafreezing and drying, fluorescence microscopy, and fluorometry. Not toxic, acriflavine had specific in vivo affinity for nuclear DNA and RNA, produced intense fluorescence, and did not pass through hematic barriers. Acriflavine was given in doses to produce the same concentrations in the systemic blood or in the aqueous humor. The exact sites of the blood-aqueous barrier, demonstrated by tracing the acriflavine fluorescence through tissues and individual cells, were in the basal cell membranes of inner ciliary and iridial epithelia and apical cell membranes of iridial and corneal endothelia. Acriflavine passed freely from the aqueous humor into the blood stream. It also followed an aqueous flow into the vitreous body and optic nerve head vessels. Interruption or reversal of this flow may cause open-angle glaucoma.

Glycogen in epidermal nerve terminals of Lacerta sicula (squamata: reptilia)

Proof is given that the granula occuring in the epidermal discoid nerve terminals of Lacerta sicula consist of glycogen. Staining with PA-PbCi shows 300 A sized alpha-particles and 70 A sized beta-particles. The electron-dense boundary appearing after digestion with alpha-amylase consists of limit-dextrins.

Energy dependence of urinary bicarbonate secretion in turtle bladder

Addition of HCO3- to the serosal side (S) of the isolated turtle bladder results in a HCO3- flow from S to the mucosal side (M) which markedly reduces the net rate of acid secretion. To characterize the driving forces for this downhill HCO3- flow, the effects of metabolic inhibitors and substrates were examined. In short-circuited bladders with the M pH lowered to the point of zero net H+ secretion, the rate of HCO3- entry into M in response to a 20-mM HCO3- gradient was measured by pH stat titration. Deoxygenation reduced the HCO3- flux from 1.24 plus or minus 0.1 mum/h/8 cm2 (SEM) to 0.50 plus or minus 0.1 muM/h with glucose (2 times 10-3 M) AND FROM 1.32 PLUS OR MINUS TO 0.47 PLUS OR MINUS 0.1 MUM/h without glucose. A similar reduction (61 per cent) was observed in the presence of 1 per cent C92. Dinitrophenol (10-4 M), cyanide (10-3 M), and deoxyglucose (10-2 M) inhibited the HCO3- flux by 39 per cent, 37 per cent, and 38 per cent, respectively. The combination of any of these inhibitors with N2 caused the same inhibition as N2 alone. In bladders depleted of substrate, pyruvate (5 times 10-3 M) increased the HCO3- flux from 0.36 plus or minus 0.05 to 0.58 plus or minus 0.01 muM/h (P smaller than 0.005); the increment was abolished by deoxygenation. The results indicate that the bulk of the downhill HCO3- flow in this system is dependent on metabolic energy derived primarily from oxidative sources, and that this energy-dependent flow approximates the electroneutral component of HCO3- secretion that is coupled to Cl- absorption.

Reptilian ovarian steroidogenesis and the influence of mammalian gonadotrophins (follicle-stimulating hormone and luteinizing hormone) in vitro

The synthesis of steroids from [7α-3H]cholesterol, [7α-3H]pregnenolone and [7α-3H]progesterone by lizard and turtle ovarian tissues in vitro was studied. Progesterone, 17α-hydroxyprogesterone, dehydroepiandrosterone, androstenedione, testosterone, oestrone and oestradiol were identified as products. In the turtle (Pseudemys), conversion of pregnenolone to progesterone was efficient, but transformation of progesterone to other steroids was relatively slow as indicated by the accumulation of progesterone over the incubation period. In Dipsosaurus, accumulation of radioactivity was greatest in testosterone, the quantities of which continued to increase at each sampling period. The rate of utilization of pregnenolone as a substrate was similar for the two species studied and the quantities of oestrone and oestradiol formed were lower in Pseudemys. The use of progesterone as precursor by Dipsosaurus ovarian tissue revealed a similar pattern of Δ4-steroid metabolism to that obtained with pregnenolone as precursor.

The effects of addition of purified follicle-stimulating hormone (FSH) and luteinizing hormone (LH) on the metabolism of [14C]cholesterol in vitro was studied using Pseudemys follicular tissue. The pattern of cholesterol metabolism was similar to that for pregnenolone in this species. The synthesis of pregnenolone, progesterone, dehydroepiandrosterone and androstenedione in vitro was significantly enhanced in the presence of LH. Follicle-stimulating hormone had no effect on steroid synthesis except for a decrease of androstenedione formation. The stimulatory effect of LH on steroidogenesis in vitro is discussed in relation to the literature suggesting that mammalian FSH, but not LH, stimulates all phases of reptilian ovarian function when injected in vivo.