Tide-related changes of blood respiratory variables in the lugworm Arenicola marina (l.)

Primitive, and protective, our cellular oxygenation status?

The primitive atmosphere where aerobic life started on earth was hypoxic and hypercapnic. Remarkably, an adaptation strategy whereby O2 partial pressure, PO2, in the arterial blood is maintained within a low and narrow range of 1-3 kPa, largely independent of inspired PO2, has also been reported in modern water-breathers. In mammalian tissues, including brain, the most frequently measured PO2 is also in the same low range. Based on the postulate that basic cellular machinery has been established since the early stages of evolution, we propose that this similarity in oxygenation status is the consequence of an early adaptation strategy which, subsequently, throughout the course of evolution, maintained cellular oxygenation in the same low and primitive range independent of environmental changes. Specialized enzymes aimed at protecting cells against O2 toxicity are thought to have appeared very early in evolution but we suggest that preventing high PO2's is also the simplest and most efficient tool for limiting reactive oxygen species (ROS) production. It could be a cue mechanism to widen our understanding of the ageing process.

From low arterial- to low tissue-oxygenation strategy. An evolutionary theory

The primitive atmosphere where aerobic life started on earth was hypoxic and hypercapnic. Remarkably, an adaptation strategy whereby O(2) partial pressure, P(O(2)), in the arterial blood is maintained within a low and narrow range of 1-3 kPa, largely independent of inspired P(O(2)), has also been reported in modern water-breathers. In mammalian tissues, including brain, the most frequently measured P(O(2)) is in the same low range. Based on the postulate that basic cellular machinery has been established since the early stages of evolution, we propose that this similarity in oxygenation status is the consequence of an early adaptation strategy which, subsequently throughout the course of evolution, maintained cellular oxygenation in the same low and primitive range independent of environmental changes. The rational for such an evolutionary theory is discussed in terms of an equilibrium between physiological and pathological reactions associated with O(2) excess vs O(2) lack and emerging concepts about the importance of cellular O(2)-dependent mechanisms in the low but physiological P(O(2)) range.

Nonvertebrate hemoglobins: functions and molecular adaptations

Hemoglobin (Hb) occurs in all the kingdoms of living organisms. Its distribution is episodic among the nonvertebrate groups in contrast to vertebrates. Nonvertebrate Hbs range from single-chain globins found in bacteria, algae, protozoa, and plants to large, multisubunit, multidomain Hbs found in nematodes, molluscs and crustaceans, and the giant annelid and vestimentiferan Hbs comprised of globin and nonglobin subunits. Chimeric hemoglobins have been found recently in bacteria and fungi. Hb occurs intracellularly in specific tissues and in circulating red blood cells (RBCs) and freely dissolved in various body fluids. In addition to transporting and storing O(2) and facilitating its diffusion, several novel Hb functions have emerged, including control of nitric oxide (NO) levels in microorganisms, use of NO to control the level of O(2) in nematodes, binding and transport of sulfide in endosymbiont-harboring species and protection against sulfide, scavenging of O(2 )in symbiotic leguminous plants, O(2 )sensing in bacteria and archaebacteria, and dehaloperoxidase activity useful in detoxification of chlorinated materials. This review focuses on the extensive variation in the functional properties of nonvertebrate Hbs, their O(2 )binding affinities, their homotropic interactions (cooperativity), and the sensitivities of these parameters to temperature and heterotropic effectors such as protons and cations. Whenever possible, it attempts to relate the ligand binding properties to the known molecular structures. The divergent and convergent evolutionary trends evident in the structures and functions of nonvertebrate Hbs appear to be adaptive in extending the inhabitable environment available to Hb-containing organisms.

Quaternary structure of the extracellular haemoglobin of the lugworm Arenicola marina: a multi-angle-laser-light-scattering and electrospray-ionisation-mass-spectrometry analysis

To elucidate the quaternary structure of the extracellular haemoglobin (Hb) of the marine polychaete Arenicola marina (lugworm) it was subjected to multi-angle laser-light scattering (MALLS) and to electrospray-ionisation mass spectrometry (ESI-MS). It was also subjected to SDS/PAGE analysis for comparative purposes. MALLS analysis gave a molecular mass of 3648 +/- 24 kDa and a gyration radius of 11.3 +/- 1.7 nm. Maximum entropy analysis of the multiply charged electrospray spectra of the native, dehaemed, reduced and carbamidomethylated Hb forms, provided its complete polypeptide chain and subunit composition. We found, in the reduced condition, eight globin chains of molecular masses 15952.5 Da (a1), 15974.8 Da (a2), 15920.9 Da (b1), 16020.1 Da (b2), 16036.2 Da (b3), 16664.8 Da (c), 16983.2 Da (d1), 17033.1 Da (d2) and two linker chains L1, 25174.1 Da, and L2, 26829.7 Da. In the native Hb, chains b, c, d occur as five disulphide-bonded trimer subunits T with masses of 49560.4 Da (T1), 49613.9 Da (T2), 49658.6 Da (T3), 49706.8 Da (T4), 49724.5 Da (T5). Linker chains L1 and L2 occur as one disulphide-bonded homodimer 2L1 (D1) of 50323.1 Da and one disulphide-bonded heterodimer L1-L2 (D2) of 51 981.5 Da. Polypeptide chains a and d possess one free cysteine residue and chains d possess an unusual total of five cysteine residues. Semi-quantitative analysis of ESI-MS data allowed us to propose the following model for the one-twelfth protomer: [(3a1)(3a2)2T] (T corresponding to either T3, T4 or T5). From electron micrograph data T1 and T2 are probably located at the centre of the molecule as mentioned in previous studies. The Hb would thus be composed of 198 polypeptide chains with 156 globin chains and 42 linker chains, each twelfth being in contact with 3.5 linker subunits, providing a total mass of 3682 kDa including haems in agreement with the experimental molecular mass determined by MALLS. From ESI-MS relative intensities and the model proposed above, the globin/linker ratio gave 0.71:0.29 and 0.73:0.27, respectively. The estimation of haem content by pyridine haemochromogen and by cyanmethaemoglobin (HiCN) methods also support the globin chain number provided by ESI-MS.

Seawater salinity and blood acid-base balance in the lugworm, Arenicola marina (L.)

The kinetics of variations in the blood acid base balance (ABB) were investigated in a moderately euryhaline osmoconformer, the lugworm Arenicola marina (L.), exposed to natural and experimental hypo- or hyperosmotic shocks. In natural as well as in experimental conditions, a hyposmotic shock induced a transient and essentially metabolic acidosis, probably linked to the ionic readjustments following the shock, which was rapidly overridden by a metabolic alkalosis. In field conditions, a new ABB equilibrium was then attained, the metabolic alkalosis being neutralized by the respiratory and metabolic acidosis occurring normally in the lugworm during low tide. Conversely, in the normoxic conditions of our laboratory experiments, a new ABB equilibrium was never reached. Under experimental conditions, a hyperosmotic shock always induced a respiratory and metabolic acidosis. In the field, this phenomenon must occur at the beginning of high tide and must help to restore normal blood ABB in lugworms submitted to a moderate hyposmotic shock during low tide. All the observed blood ABB variations reveal the complex intracellular processes through which the lugworm submitted to moderate osmotic shocks tentatively regulates, sometimes without any real success, its osmoticity and volume. Obviously, complementary physical, physiological and behavioral mechanisms allow the lugworm to live in sediments washed by almost fresh water during a 7-8 h 'low tide'.

Ventilation and respiratory gas exchanges of the lugworm Arenicola marina (L.) as functions of ambient PO2 (20-700 torr)

Ventilatory regulation of intact, unrestrained lugworms Arenicola marina living in glass-tube artificial burrows was examined for values of inspired seawater PO2, PIO2, from 20 to 700 torr, at constant ambient pH and PCO2 values. The water ventilation rate and the respiratory characteristics of the ventilated seawater were measured. The water convection requirement and the corresponding specific rates of O2 uptake and CO2 production were calculated. The mean ventilatory water flow was a complex function of PIO2: decrease in hyperoxia, increase in hypoxia, decrease in extreme hypoxia. Compared to the normoxic responses, hyperoxia led to a hypercapnia (and acidosis) and moderate hypoxia to a hypocapnia (and alkalosis) in the expired water, variations which presumably reflect blood acid-base balance changes. Thus, as in other water breathers, the regulation of the organism's oxygenation may override the regulation of its acid-base balance. The lugworm's oxygen exchanger is highly efficient. However, below a critical partial pressure, PIO2 ca 120 torr, values of O2 consumption and ventilation decreased. A second critical O2 partial pressure appeared at PIO2 values between 80 and 40 torr; a 'switch-on' of anaerobic metabolism. These phenomena may be viewed as features of an adaptative respiratory strategy selected for in relation with the lugworm's particular peristaltic ventilatory mechanism and its intertidal mode of life.

Molecular architecture of annelid erythrocruorins. Extracellular hemoglobin of Arenicola marina (Polychaeta)

The respiratory protein, erythrocruorin, of the annelid Arenicola marina was investigated. Spectral properties show many analogies with those of vertebrate hemoglobine. 144 heme groups (ferroprotoporphyrin) were found in the whole molecule, which has a relative molecular mass of 3.56 X 10(6), as determined by sedimentation equilibrium, and an isoelectric point of 4.69. Protein dissociation patterns were analysed by electrophoresis after denaturation in the presence of dodecylsulfate, with and without 2-mercaptoethanol. A tentative model associating molecular mass of the native molecule, heme content, molecular mass of the polypeptide chains and functional properties is proposed. A twelfth subunit of A. marina erythrocruorin would contain twelve heme groups arranged in three functional units made up of four protomers, half of these being covalently bound to non-heme chains; two structural chains would be spatially arranged as bonds between the subunits.

Recovery of volatile fatty acids from biological materials for direct analysis by gas chromatography

A simple and efficient methodology for preparing aqueous extracts of volatile fatty acids from biological materials, for direct analysis by gas chromatography is described. Peak areas and responses relative to n-butyric acid were used to calculate concentrations of the individual acids. An example is given for analysis of the volatile fatty acids found in the blood of the lugworm Aerinocola marina.

Temperature-induced variations of blood acid-base status in the lugworm, Arenicola marina (L.): II. In vivo study

Lugworms, Arenicola marina (L.), acclimatized at 16-17 degrees C, were acclimated at temperatures between 5.3 and 25.7 degrees C for 96 h. Whereas in vitro Arenicola blood behaves like a Rosenthal system, in vivo prebranchial blood does not: the higher the acclimation temperature, the lower the pHv and [HCO3]V, PVCO2, remaining practically constant. Nevertheless, the very low relative alkalinity of the blood in vivo ([OH-]/[H+] is less than 3), and the degree of dissociation of extra- and intracellular proteins, remain practically constant whatever the temperature. From examples in the literature together with these results, it is concluded that poikilothermic air-breathers and poikilothermic water-breathers regulate their blood pH in the face of temperature changes by contrasting mechanisms. In the first, regulation is almost instantaneous and takes place at the pulmonary level through adjustment of CO2 exchanges. In the second this regulation is slow and mainly extraventilatory, occurring through ionic exchanges. This contrast must be considered in relation with differences in blood PCO2 values, caused by the much higher O2 capacitance of air compared to water.

Temperature-induced variations of blood acid-base status in the lugworm, Arenicola marina (L.): I. In vitro study

Blood of the lugworm Arenicola marina studied in vitro behaved like a Rosenthal system: when temperature rose, pH decreased and PCO2 increased, whereas [HCO3] remained practically constant. pH values were low whatever the CCO2 and SO2. The temperature coefficient dpH/dt was always significantly different from the mean temperature-induced variations of the neutral pH of pure water between 0 and 30 degrees C. Consequently, the relative alkalinity of the blood, [OH-]/[H+], was very low (range, 1.53-5.06) and increased appreciably with temperature. Calculated changes in the fractional dissociation of protein imidazole groups, alphaIm, were smaller. The very variable buffer power of Arenicola hemoglobin was maximum (beta max) for a strictly defined, temperature-dependent value of pH (pH beta max), suggesting that as yet unidentified ionizable group on the hemoglobin molecule, RH, could be responsible for the pH-dependent changes of blood buffer power in Arenicola. Assuming pK'RH = PH beta max, the calculated fractional dissociation of RH, alpha RH, was constant between 0 and 30 degrees C. The nature of RH is discussed in relation with Reeves's hypothesis concerning the preeminence of protein imidazole groups in the regulation of extra- and intracellular pH.