Inhibition of prostaglandin E1-induced activation of adenylate cyclase in human blood platelet membrane

Activation of human blood platelet adenylate cyclase is initiated through the binding of prostaglandin E1 to the membrane receptors. Incubation of platelet membrane with [3H]prostaglandin E1 at pH 7.5 in the presence of 5 mM MgCl2 showed that the binding of the autacoid was rapid, reversible and highly specific. The binding was linearly proportional to the activation of adenylate cyclase. Although the membrane-bound radioligand could not be removed either by GTP or its stable analogue 5'-guanylylimido diphosphate, 150 nM cyclic AMP displaced about 40% of the bound agonist from the membrane. Scatchard analyses of the binding of the prostanoid to the membrane in the presence or absence of cyclic AMP showed that the nucleotide specifically inhibited the high-affinity binding sites without affecting the low-affinity binding sites. Incubation of the membrane with 150 mM cyclic AMP and varying amounts of prostaglandin E1 (25 nM to 1.0 microM) showed that the percent removal of the membrane-bound autacoid was similar to the percent inhibition of adenylate cyclase at each concentration of the agonist. At a concentration of 25 nM prostaglandin E1, both the binding of the agonist and the activity of adenylate cyclase were maximally inhibited by 40%. With the increase of the agonist concentration in the assay mixture, the inhibitory effects of the nucleotide gradually decreased and at a concentration of 1.0 microM prostaglandin E1 the effect of the nucleotide became negligible. These results show that cyclic AMP inhibits the activation of adenylate cyclase by low concentrations of prostaglandin E1 through the inhibition of the binding of the agonist to high-affinity binding sites.

Colony-stimulating factor 1-induced Na+ influx into human monocytes involves activation of a pertussis toxin-sensitive GTP-binding protein

Colony-stimulating factor 1 (CSF-1) regulates the survival, growth, and differentiation of monocytes through binding to a single class of high affinity receptors. The present studies demonstrate that the interaction of CSF-1 with monocyte membranes is associated with a 2.4-fold increase in specific binding of the GTP analogue, GTP gamma S. Scatchard analysis of the GTP gamma S binding data indicated that CSF-1 stimulates GTP binding by increasing the affinity, rather than the number, of available sites. This stimulation of GTP binding by CSF-1 was also associated with an increase in GTPase activity. Furthermore, the CSF-1-induced stimulation of GTPase activity was sensitive to pertussis toxin. We also demonstrate that CSF-1 stimulates Na+ influx into monocytes by an amiloride-sensitive mechanism, presumably the Na+/H+ antiport. This CSF-1-stimulated influx of Na+ was further associated with an increase in Na+,K+-ATPase activity. Moreover, this stimulation of Na+ influx and Na+,K+-ATPase activity by CSF-1 was sensitive to pertussis toxin. Finally, we demonstrate that CSF-1-induced proliferation is also a pertussis toxin-sensitive event. The present findings thus suggest: 1) that the CSF-1 receptor is linked to a pertussis toxin-sensitive G protein; and 2) that a pertussis toxin-sensitive G protein is involved in the induction of Na+ influx by CSF-1.

Gn-proteins are distinct from ras p21 and other known low molecular mass GTP-binding proteins in the platelet

The 27 kDa platelet membrane protein (Gn27) that binds [alpha-32P]GTP on nitrocellulose blots of SDS-polyacrylamide gels [(1987) Biochem. J. 245, 617-620] was compared with other low molecular mass GTP-binding proteins. Platelet membranes also contained 21 kDa proteins that bound anti-ras p21 antibody and 22-23 kDa proteins that could be ADP-ribosylated by botulinum neurotoxin type D. These groups of proteins were resolved electrophoretically from each other and from Gn27. A low molecular mass GTP-binding protein from bovine brain [(1987) Biochem. J. 246, 431-439] was also resolved from Gn27. At the levels normally present in cell membranes, only Gn-proteins bound significant amounts of [32P]GTP after transfer of protein from SDS-polyacrylamide gels to nitrocellulose.

GTP gamma S-stimulated hydrolysis of phosphatidylinositol-4,5-bisphosphate soluble phospholipase C from human platelets requires soluble GTP-binding protein

GTP-binding activity was fractionated into two peaks (GI and GII) by chromatography on heparin-agarose. GTP-dependent PLC activity eluted as a single peak, which co-chromatographed with GTP-binding peak GII. Rechromatography of peak GII on heparin-agarose, in the presence of 0.5% sodium cholate, resulted in separation of PLC and GTP-binding activities, and loss of GTP-dependent PLC activity. Recombining fractions containing PLC and GTP-binding activities restored GTP-dependent PLC activity. A specific GTP-binding protein of 29,000 daltons was identified in peak GII by Western blotting of column fractions with [alpha-32P]GTP. These results demonstrate that the soluble phospholipase C from human platelets is regulated by GTP S-binding protein (G29).

The adrenergic responses of carp (Cyprinus carpio) red cells: effects of PO2 and pH

Carp (Cyprinus carpio) red cells do not show beta-adrenergic responses when incubated with 10(−5) mol l-1 adrenaline at atmospheric oxygen tension and a pH value close to the in vivo resting pH (approx. 8.1). However, when either the pH or the oxygen tension of the incubation medium is decreased, the adrenergic responses appear, showing that oxygen or an oxygen-linked phenomenon has a direct influence on the response. Once present, the adrenergic red cell response is similar to that of trout: cellular water content, sodium content and intracellular pH all increase. Quantitatively the effect appears to be much smaller in carp than in trout. Adrenaline induces an increase in red cell oxygen content when the oxygen content is plotted as a function of extracellular pH. This effect coincides with the onset of the Root effect and is caused by the adrenaline-induced increase in intracellular pH, since it disappears when the oxygen content is plotted as a function of intracellular pH. The red cell ATP content decreases metabolically during adrenaline incubations. In contrast, cellular GTP content is not metabolically reduced in adrenaline-treated cells, showing that the rapid and selective decrease in red cell GTP concentration, observed in hypoxic cyprinids, is not adrenergically induced.

Solubility of nitrogen and argon in eel whole blood and its relationship to pH

The solubility coefficients (alpha) for the inert gases, nitrogen (N2) and argon (Ar), were measured by mass spectrometry in whole blood of the freshwater-adapted European eel, Anguilla anguilla, at varied pH and at two temperatures, 5 and 15 degrees C. The pH was altered either by varying PCO2 (0.75-75 mmHg; 1 mmHg = 133.3 Pa) or by adding fixed acid (HCl or lactic acid). No dependence of alpha on pH (range 5.5-8.4) or on lactate concentration (range 0.2-25 mmol l-1) was detectable. Average values (+/− S.D.) for alpha (mumol l-1 mmHg-1) were: alpha N2 = 1.25 +/− 0.01, alpha Ar = 2.60 +/− 0.05 at 5 degrees C and alpha N2 = 1.09 +/− 0.03, alpha Ar = 2.12 +/− 0.07 at 15 degrees C. These data yield values for Q10 of 0.87 for nitrogen and 0.82 for argon, and for activation energy, Ea (kJ mol-1 K-1), of −9.2 for nitrogen and −13.4 for argon. The results do not support earlier reports on significant pH dependence of alpha in eel blood and suggest, in contrast, that no fundamental differences exist in respect of inert gas solubility between whole blood of the eel and of other vertebrates.

Heparin uncouples alpha 2-adrenoceptors from the Gi-protein in membranes of human platelets

The influence of heparin was studied on the inhibitory regulation of adenylate cyclase in human platelet membranes. Heparin blocked the adrenaline-induced inhibition of adenylate cyclase and the stimulation of GTP hydrolysis with half-maximal and maximal efficiency at 0.3 and 1-3 micrograms/ml, respectively. The effect of heparin was reversed by washing the membranes. Heparin did not change the number of alpha-adrenoceptors. In contrast, the affinity of the alpha-adrenoceptor for adrenaline was decreased in the presence of heparin. The pertussis toxin-catalysed ADP-ribosylation of the inhibitory guanine nucleotide-binding Gi-protein was not altered by heparin. Heparin also abolished the inhibition of adenylate cyclase caused by GTP itself. The data indicate that heparin can impair the hormone-induced inhibition of adenylate cyclase and the stimulation of GTP hydrolysis and suggest that the effects of heparin are caused by an action at the Gi-protein of the adenylate cyclase system.

Persistent jaundice after hepatic porto-jejunostomy in biliary atresia: are the patients' prognoses determined within 3 months after surgery?

Eighteen patients with biliary atresia who showed persistent jaundice after hepatic porto-jejunostomy were studied clinically. It was revealed that: 1) Patients who had abnormally high preoperative values of laboratory data showed persistent jaundice; 2) high portal pressure occurred frequently in patients with persistent jaundice; 3) most patients of persistent jaundice had a history of postoperative cholangitis; 4) in contrast to jaundice-free patients, those with persistent jaundice tended to show elevation in gamma-globulin, TTT and gamma-GTP in the early postoperative period. These results suggest that for patients showing an upward tendency in these laboratory data after surgery, carefully management should be taken, even if the serum bilirubin level continue to decrease.

Acute exposure to graded levels of hypoxia in rainbow trout (Salmo gairdneri): metabolic and respiratory adaptations

We have studied the mechanisms of acute hypoxia tolerance in rainbow trout (Salmo gairdneri). Fish held at 9 degrees C were exposed to various levels of hypoxia for 24 h. At an environmental PO2 of 30 Torr, the fish showed an initial plasma acidosis probably of metabolic origin which was subsequently offset such that blood pH returned to normal within about 4 h. Over this time period, red cell pH was maintained constant. Comparing the effects of different levels of hypoxia following 24 h exposure, oxygen consumption of the animal remained unchanged over a broad range of inspired oxygen tensions but declined by over 30% of normoxic values at inspired water PO2 levels of 80 Torr. This appeared to be a true metabolic depression because signs of increased anaerobic metabolism did not occur until there was a further reduction in water oxygen levels. Rainbow trout appear to be able to maintain a relatively high energy status in their white muscle during 24 h exposure to severe hypoxia (water PO2 = 30 Torr). As the level of hypoxia was intensified, there was a reduction in the oxygen gradient across the gills, probably facilitated in part by the release of catecholamines into the blood. The erythrocytic ATP: Hb4 molar ratios declined with increasing hypoxic stress as did the pH gradient between the erythrocyte and plasma. The overall effect was no change in Hb O2-affinity after 24 h exposure to severe hypoxia.

Identification and purification of a novel G protein from neutrophils

A novel G protein which appears to couple chemotactic peptide receptors to a polyphosphoinositide phospholipase C has been purified from rabbit neutrophils. Neutrophil membranes were solubilized with sodium cholate and fractionated by successive anion exchange, gel filtration and hydrophobic chromatography. Guanosine-5'-(3-O-thio)triphosphate binding activity was purified 170-fold from the soluble extract. The alpha-subunit of the purified G protein was identified by pertussis toxin-catalyzed ADP-ribosylation, and found to have an Mr of 40,000. The beta-subunit (Mr 36,000) comigrated on SDS-polyacrylamide gel electrophoresis with the beta-subunits of bovine brain Gi and Go. The neutrophil pertussis toxin substrate is highly unstable in cholate solution unless 30% ethylene glycol is added. Structural and functional analysis of this novel G protein will advance our understanding of the molecular mechanisms of coupling of receptors to phospholipase C.

Detection of 23-27 kDa GTP-binding proteins in platelets and other cells

Membrane proteins from rabbit and human platelets were separated by SDS/polyacrylamide-gel electrophoresis and the resolved polypeptides blotted on nitrocellulose. A family of GTP-binding proteins, termed Gn proteins, was detected by incubation of these blots with [alpha-32P]GTP in the presence of Mg2+. A major Gn protein with a molecular mass of 27 kDa (Gn27) and lesser amounts of 23, 24 and 25 kDa Gn proteins were observed in platelet membranes; much smaller amounts were in the platelet soluble fraction. Binding of [alpha-32P]GTP by platelet Gn proteins was blocked by GDP, GTP or guanosine 5'-[gamma-thio]triphosphate, but not by GMP or adenosine 5'-[beta gamma-imido]triphosphate. Rabbit and human red-cell membranes contained only Gn27. When rat tissues were analysed for Gn proteins, the largest amounts were found in brain, which contained two membrane-bound forms (Gn27 and Gn26) and a soluble form (Gn26).

Purification and immunochemical characterization of the major pertussis-toxin-sensitive guanine-nucleotide-binding protein of bovine-neutrophil membranes

Bovine peripheral neutrophils contain high levels of a 40-kDa pertussis toxin substrate, which was found highly enriched in a light membrane fraction upon subcellular fractionation of neutrophil homogenates. The 40-kDa pertussis toxin substrate, referred to as alpha n, was purified to near homogeneity from this fraction by sequential ion-exchange, gel-filtration and hydrophobic chromatography. Purified alpha n was shown to interact with beta gamma subunits, undergo ADP-ribosylation by pertussis toxin, and bind guanine nucleotides with high affinity. The mobility of purified alpha n on SDS/polyacrylamide gels was intermediate between those of the alpha subunits of Gi and Go, purified from bovine brain, and slightly lower than the mobility of the alpha subunit of transducin (Gt). Several polyclonal antisera against the alpha subunits of bovine Gt and Go did not react with alpha n on immunoblots. CW 6, a polyclonal antiserum reactive against the bovine alpha i, reacted only minimally with alpha n. These results suggest that the major pertussis toxin substrate of bovine neutrophils, designated Gn, is structurally different from previously identified pertussis toxin substrates and may represent a novel guanine-nucleotide-binding protein.

Specific binding of [alpha-32P]GTP to cytosolic and membrane-bound proteins of human platelets correlates with the activation of phospholipase C

We have assessed the binding of [alpha-32P]GTP to platelet proteins from cytosolic and membrane fractions. Proteins were separated by NaDodSO4/PAGE and electrophoretically transferred to nitrocellulose. Incubation of the nitrocellulose blots with [alpha-32P]GTP indicated the presence of specific and distinct GTP-binding proteins in cytosol and membranes. Binding was prevented by 10-100 nM GTP and by 100 nM guanosine 5'-[gamma-thio]triphosphate (GTP[gamma S]) or GDP; binding was unaffected by 1 nM-1 microM ATP. One main GTP-binding protein (29.5 kDa) was detected in the membrane fraction, while three others (29, 27, and 21 kDa) were detected in the soluble fraction. Two cytosolic GTP-binding proteins (29 and 27 kDa) were degraded by trypsin; another cytosolic protein (21 kDa) and the membrane-bound protein (29.5 kDa) were resistant to the action of trypsin. Treatment of intact platelets with trypsin or thrombin, followed by lysis and fractionation, did not affect the binding of [alpha-32P]GTP to the membrane-bound protein. GTP[gamma S] still stimulated phospholipase C in permeabilized platelets already preincubated with trypsin. This suggests that trypsin-resistant GTP-binding proteins might regulate phospholipase C stimulated by GTP[gamma S].

G-protein dissociation, GTP-GDP exchange and GTPase activity in control and PMA treated neutrophils stimulated by fMet-Leu-Phe

The addition of the chemotactic factor fMet-Leu-Phe to cell homogenates causes a decrease in the pertussis toxin catalyzed ADP-ribosylation of a 41 kDa protein. The fMet-Leu-Phe induced decrease is not abolished in homogenates prepared from phorbol 12-myristate 13-acetate treated neutrophils. This decreased ribosylation probably reflects a dissociation of the GTP-binding protein oligomer that is not followed by association, possibly because of the release of the alpha-subunit into the suspending medium. Furthermore, fMet-Leu-Phe stimulates the binding of radiolabelled guanylylimidodiphosphate to membrane preparations. Again, the stimulated binding of guanylylimidodiphosphate is not affected by treating the intact neutrophils with phorbol 12-myristate 13-acetate. In addition leukotriene B4, platelet activating factor and fMet-Leu-Phe activate a high-affinity GTPase in membrane preparations. The basal level of this GTPase activity is dramatically inhibited in membrane preparations isolated from cells treated with phorbol 12-myristate 13-acetate. On the other hand, the fMet-Leu-Phe stimulated component is only marginally reduced. The present findings suggest that PMA does not prevent receptor G-protein interaction.

Evidence for two GTPases activated by thrombin in membranes of human platelets

Thrombin inhibits adenylate cyclase and stimulates GTP hydrolysis by high-affinity GTPase(s) in membranes of human platelets at almost identical concentrations. Both of these thrombin actions are similar to those observed with agonist-activated alpha 2-adrenoceptors coupling to the inhibitory guanine nucleotide-binding protein N1. However, stimulation of GTP hydrolysis caused by adrenaline (alpha 2-adrenoceptor agonist) and by thrombin at maximally effective concentrations was partially additive, whereas with regard to adenylate cyclase inhibition no additive response was observed. Furthermore, treatment of platelet membranes with pertussis toxin, which inactivates Ni and largely abolishes thrombin- and adrenaline-induced adenylate cyclase inhibition and adrenaline-induced GTPase stimulation, decreased the thrombin-induced stimulation of GTP hydrolysis by only about 30%. Additionally, the thiol reagent N-ethylmalemide (NEM) at rather low concentrations abolished thrombin- and adrenaline-induced stimulation of GTP hydrolysis was decreased by only 30-40% by treatment of platelet membranes with even high concentrations of NEM. Treatment with cholera toxin, which inhibits GTPase activity of the Ns (stimulatory guanine nucleotide-binding) protein, has no effect on thrombin-stimulated GTP hydrolysis. The data suggest that thrombin interaction with its receptor sites in platelet membranes leads to stimulation of two GTP-hydrolysing enzymes. One of these enzymes is apparently Ni and is also activated by agonist-activated alpha 2-adrenoceptors and is inactivated by pertussis toxin and NEM treatment. The other GTP-hydrolysing enzyme activated by thrombin may represent a guanine nucleotide-binding protein apparently involved in the coupling of thrombin receptors to the phosphoinositide phosphodiesterase.

Blood respiratory properties of the mudsucker fish Labeo capensis (Smith)

For Labeo capensis (Smith) the increase in blood organic phosphates (ATP, GTP) in winter fish exceeds the increase in summer fish. Blood chlorides, blood osmotic pressure, hematocrit and hemoglobin concentration decrease significantly in winter fish when compared to summer fish. Four effectors, viz. temperature, organic phosphates, H+ and Cl-, could lower the oxygen affinity of whole blood, especially in summer fish.

Z-nucleotide accumulation in erythrocytes from Lesch-Nyhan patients

5-Amino-4-imidazolecarboxamide riboside 5'-monophosphate (ZMP) is an intermediate in the purine de novo synthetic pathway that may be further metabolized to inosine 5'-monophosphate, degraded to the corresponding nucleoside (5-amino-4-imidazole-carboxamide riboside; Z-riboside), or phosphorylated to the corresponding 5'-triphosphate (ZTP). Accumulation of ZTP in microorganisms has been associated with depletion of folate intermediates that are necessary for the conversion of ZMP to inosine 5'-monophosphate and has been postulated to play a regulatory role in cellular metabolism. We have shown the presence of Z-nucleotides in erythrocytes derived from five individuals with the Lesch-Nyhan syndrome. Erythrocyte folate levels were within the normal range, although guanosine triphosphate levels were significantly reduced below those in normal controls (P less than 0.01). A small amount of Z-nucleotide accumulation was also found in one individual with partial deficiency of the enzyme hypoxanthine guanine phosphoribosyltransferase and in two individuals with other disorders of purine overproduction. In contrast, no Z-nucleotides were detected in 13 normal controls or in three individuals with hyperuricemia on allopurinol therapy. We conclude that Z-nucleotide formation may result from markedly increased rates of de novo purine biosynthesis. It is possible that metabolites of these purine intermediates may play a role in the pathogenesis of the Lesch-Nyhan syndrome.

Evidence that the primary effect of phosphorylation of eukaryotic initiation factor 2(alpha) in rabbit reticulocyte lysate is inhibition of the release of eukaryotic initiation factor-2.GDP from 60 S ribosomal subunits

The phosphorylation of eukaryotic initiation factor (eIF) 2 alpha that occurs when rabbit reticulocyte lysate is incubated in the absence of hemin or with poly(I.C) causes inhibition of polypeptide chain initiation by preventing a separate factor (termed RF) from promoting the exchange of GTP for GDP on eIF-2. When lysate was incubated in the presence of hemin and [14C] eIF-2 or [alpha-32P]GTP, we observed binding of eIF-2 and GDP or GTP to 60 S ribosomal subunits that was slightly greater than that bound to 40 S subunits and little binding to 80 S ribosomes. When incubation was in the absence of hemin or in the presence of hemin plus 0.1 microgram/ml poly(I.C), eIF-2 and GDP binding to 60 S subunits was increased 1.5- to 2-fold, that bound to 80 S ribosomes was almost as great as that bound to 60 S subunits, and that bound to 40 S subunits was unchanged. Our data indicate that about 40% of the eIF-2 that becomes bound to 60 S subunits and 80 S ribosomes in the absence of hemin or with poly(I.C) is eIF-2(alpha-P) and suggest that the eIF-2 and GDP bound is probably in the form of a binary complex. The accumulation of eIF-2.GDP on 60 S subunits occurs before binding of Met-tRNAf to 40 S subunits becomes reduced and before protein synthesis becomes inhibited. The rate of turnover of GDP (presumably eIF-2.GDP) on 60 S subunits and 80 S ribosomes in the absence of hemin is reduced to less than 10% the control rate, because the dissociation of eIF-2.GDP is inhibited. Additional RF increases the turnover of eIF-2.GDP on 60 S subunits and 80 S ribosomes to near the control rate by promoting dissociation of eIF-2.GDP but not eIF-2(alpha-P).GDP. Our findings suggest that eIF-2.GTP binding to and eIF-2.GDP release from 60 S subunits may normally occur and serve to promote subunit joining. The phosphorylation of eIF-2 alpha inhibits polypeptide chain initiation by preventing dissociation of eIF-2.GDP from either free 60 S subunits (thus inhibiting subunit joining directly) or the 60 S subunit component of an 80 S initiation complex (thereby blocking elongation and resulting in the dissociation of the 80 S complex).

Human platelet adenylate cyclase: persistent binding of guanine nucleotide is central to the regulation of both hormone-stimulated and basal activities

Prostaglandin E1 stimulation of human platelet adenylate cyclase, in purified plasma membranes, occurs without the addition of exogenous GTP. Possible contamination of the adenylate cyclase assay mixture by GTP either from nonspecifically bound nucleotide in the plasma membrane or from the substrate ATP was ruled out as follows: (a) variation of the membrane concentration, repeated washing, inclusion of EDTA, GDP beta S, or GMP in the wash step, or UDP in the assay, are all without effect, and (b) analysis of the substrate by high-performance liquid chromatography revealed no contaminating GTP. Other prostaglandins (I2, E2, D2) also activate cyclase without the addition of GTP. In sharp contrast, stimulation of adenylate cyclase in the human neutrophil plasma membrane by prostaglandin E1 shows an obligatory requirement for GTP, under identical assay conditions. GDP beta S pretreatment amplifies the fold cyclase stimulation by GTP in the presence and absence of prostaglandin E1, by lowering the basal activity. This alteration occurs without lowering the GTP-independent prostaglandin E1 activation, and is specific for inhibitory guanine nucleotides (GDP beta S, GMP, GDP) in the pretreatment. Extensive washing with buffer or incubation with other nucleotides, epinephrine, or prostaglandin E1 prior to the assay, is without effect. GTP gamma S treatment of the membrane induces a high-activity state and abolishes the GDP beta S effect on basal activity as well as prostaglandin E1 activation of cyclase. The results suggest distinct patterns of prostaglandin stimulation in platelet and neutrophil cyclase systems, and further imply that guanine nucleotide, prebound to specific sites within the GTP-regulatory proteins, may modify the kinetic characteristics of platelet adenylate cyclase.

Metastatic uveal melanoma. Pretherapy serum liver enzyme and liver scan abnormalities

The liver was the organ most frequently involved in 50 patients with primary melanomas of the choroid or ciliary body, who were treated with enucleation or cobalt plaque radiotherapy and who subsequently developed systemic metastasis. Forty-seven (94%) of the patients had clinical or laboratory evidence of liver metastasis. The median survival time following treatment of the primary choroidal melanoma was 28 months (range, 7.7 to 123.1 months). Results of pretreatment studies, including serum liver enzyme levels, liver scans, or both, were abnormal in six (12%) of the patients studied. As a group, the eight patients who died within one year following ocular surgery had a significantly higher prevalence of pretreatment laboratory abnormalities. Extraocular extension of the choroidal melanoma was also present in four (50%) of these eight patients. Conversely, no patient who survived longer than the median survival period (28 months) had abnormal pretreatment laboratory findings.

Metabolism of guanosine in human erythrocytes

The metabolism of guanosine in human erythrocytes has been studied in two different experimental systems--direct incubation and dialysis incubation--the latter allowing continuous addition and removal of substances. Intra- and extracellular purine compounds were analyzed using high-performance liquid chromatography (HPLC). At 37 degrees C, a normal pH (7.4) and a favorably high concentration of inorganic phosphate, guanine nucleotides were synthesized at a substance rate of about 0.17 mmol . h-1 (calculated per liter erythrocytes) when guanosine was kept at a concentration of 25 mumol . l-1. At a higher guanosine concentration the rate of synthesis increased only moderately. Erythrocytes loaded with guanylates lost these nucleotides at a rate of 0.023 mmol . h-1 at a normal phosphate concentration and somewhat slower at a higher phosphate concentration. The metabolism kept the guanylates in an equilibrium that was similar to the equilibrium between the adenylates.

Changes in blood metabolites following stress from capture and handling of the marine teleost Girella tricuspidata

Whole blood nucleoside triphosphate (NTP) and lactate in the parore (Girella tricuspidata, Fam: Kyphosidae) were monitored over a period of 12 hr following capture by gill net. An increase in NTP during the post-capture recovery period was mainly attributable to a significant rise (P less than 0.05) in the NTP component guanosine triphosphate (GTP). The rise in GTP levels correlated with the decline in blood lactate (r = -0.72) accumulated during the period of capture stress. It is suggested that metabolism of lactate via the Krebs cycle may be responsible for the rise in GTP.

Temperature acclimation and oxygen binding properties of blood of the European eel, Anguilla anguilla

Temperature acclimation of the European eel, Anguilla anguilla, resulted in red cell GTP/Hb molar ratios of 1.20, 1.77 and 0.80 at 2, 17 and 29 degrees C, respectively. A small increase in blood oxygen capacity was present in 29 degrees C acclimated eels. The CO2 Bohr effect and the shape of the oxygen binding curve (n-Hill) were invariant with both temperature and GTP/Hb. The significant differences in the GTP/Hb ratio corresponded with a strong enhancement of the temperature effect on blood oxygen affinity between 2 and 17 degrees C and a similarly strong compensation between 17 and 29 degrees C. Predicted in vivo P50 values were 3.0, 13.8 and 17.6 mmHg at 2 degrees C, 17 and 29 degrees C, respectively. The adaptational value of these findings are discussed in relation to standard metabolic rates at the various temperatures. A tentative hypothesis is proposed that the present study confirms and expands earlier work and supports the contention that adjustments in blood oxygen affinity of thermally acclimated teleosts serve to provide them with an unloading O2 tension for diffusion closely matching the standard oxygen requirements at the various temperatures.