Influence of intracellular pH on reduction of energy metabolism during hypoxia in the lugworm Arenicola marina

Abstract

The influence of intracellular pH (pHi) on the energy metabolism during hypoxia was studied in the lugworm Arenicola marina using in vivo 31P nuclear magnetic resonance (NMR) spectroscopy and biochemical analysis of the metabolic end products during hypoxia. By addition of phenylphosphonic acid (PPA) to the incubation medium to increase the extracellular H + buffering capacity, different degrees of intracellular acidosis during hypoxia could be attained.At low extracellular PPA concentrations pHi dropped within 1 2 h of hypoxia from 7.3 to 6.7. High extracellular PPA concentrations (50 mM) kept pHi stable at 7.2. Glycogenolysis was enhanced during hypoxia at high pHi, as shown by the measured amounts of accumulated end products. ATP production at high pHi was 31 pmol/g h vs. 15 at low pHi. The mobilisation of the phosphagen phosphotaurocyamine (PTC) was, in contrast, decreased at high pHi: the ratio PTC/p-ATP dropped from 4.8 (normoxia) to 2.8 at high vs. 1.3 at low pHi. The reduction of the metabolic rate during hypoxia hence depends on intracellular acidosis: the rate of the Embden-Meyerhof-Parnas pathway at high pHi was 4.5 kmol/g h vs. 1.9 at low pHi.The lugworm Arenicola marina lives in the tidal zone of the sea coast, where during low tide it regularly has to cope with prolonged periods of environmental hypoxia. During hypoxia the energy demand is largely compensated by anaerobic ATP production particularly due to the degradation of aspartate and glycogen to alanine, strombine, acetate, and propionate (Schottler et al., '84; Siegmund et al., '85). The rate of anaerobic energy production, however, is not constant during prolonged periods of hypoxia. It decreases within 24 hours from 40 pmol ATP/h g dry weight to 9 pmol/h g dry weight (Schottler, '86).Such a reduction in ATP production and consumption has been observed in several animals which are able to survive prolonged periods of hypoxia (for review see Gade, '83; Storey, '85a) and it might be an important strategy for saving energy stores and preventing poisoning due to the accumulation of metabolic end products during hypoxia (cf. Hochachka, '86).Our knowledge about the mechanisms regulating the reduction of energy production and consumption are very sparse (cf. Hochachka and Somero, '84; Hochachka and Guppy, '87; Wegener, '88). Due to the general relevance of pH on enzyme activity, a decrease of intracellular pH has been related with the inhibition of the various metabolic pathways during hypoxia (for a review, cf. Roos and Boron, '81; Nuccitelli and Heiple, '82). Studies on the regulatory enzyme of glycolysis, phosphofructokinase (PFK), concerning the flux through the Embden-Meyerhof-Parnas (EMP) pathway evidenced a drastic reduction of the enzyme's activity when pH decreased (Ui, '66; Ebberink, '82). Other findings on molluscs imply that a drop in fructose 2,6-bisphosphate concentration (Storey, '85b) or that a covalent modification of PFK prevents the activation of this enzyme and thereby a Pasteur effect (Storey, '84). Preliminary in v...

The diversification of the antimicrobial peptides from marine worms is driven by environmental conditions

“…Arenicin (ARE) was purified from the lugworm Arenicola marina (Annelid, Polychaeta, Scolecida), a polychaete that inhabits temperate near-shore (intertidal) sediments, digging tunnels in the sand (HOBSON, 1967;Riisgard and Banta, 1998). The burrows of these worms are exposed to periodic tidal emersion, which imposes severe thermal variations (-5 °C to 25 °C) and temporal hypoxia with mild acidic conditions (pH from 5.6 to 8.2) (Alyakrinskaya, 2003;Bat and Raffaelli, 1998;Juretschke and Kamp, 1990;Shumway and Davenport, 1977;Sommer et al, 1997;Pörtner, 1999, 2002;Toulmond, 1975;Weber, 1979). Polaricin (POL) was identified by homology search in the transcriptome of Amphitritides sp.…”

“…The antimicrobial efficacy was tested either at 10 °C, which corresponds to the optimal temperature of Arenicola marina (A. Sommer, 1999;Alyakrinskaya, 2003;Bat and Raffaelli, 1998;Juretschke and Kamp, 1990;Shumway and Davenport, 1977;Sommer et al, 1997;Sommer and Pörtner, 2002;Toulmond, 1975;Weber, 1979) or at 42 °C, which corresponds to the optimal temperature of A. pompejana (Desbruyères et al, 1998;Di Meo-Savoie et al, 2004;Gaill and Le Bris, 2007;Le Bris et al, 2005;Ravaux et al, 2013;Von Damm, 2000). The assay was first adjusted according to the growth curve of the bacteria previously determined at the different temperatures (Fig.…”

Resistance to freshwater exposure in White Sea Littorina spp. II: Acid-base regulation

“…A decrease of intracellular pH (pH i ) may have adverse e ects on enzyme functions and intracellular energy transductions (PoÈ rtner 1987a(PoÈ rtner , 1993. Although an extreme drop in pH i would have deleterious e ect on cellular functions, a moderate decrease may be advantageous during anoxia, providing a necessary background for slowing down enzymatic reactions and for improving protein stability, hence contributing to metabolic arrest (Juretschke and Kamp 1990;Kamp 1993;PoÈ rtner 1993;Hand and Hardewig 1996;Schmidt and Kamp 1996).…”

Oxygen, pHi and arrest of biosynthesis in brine shrimp embryos

“…Because of the complex interplay among pH acidi®cation, PFK±actin interaction and the PFK tetramer-dimer equilibrium, one might predict an activation of PFK with moderate acidosis and then inhibition under severe conditions (pH £ 6.7) due to PFK depolymerization (Somero & Hand 1990, Somero et al 1991. Juretschke & Kamp (1990) experimentally addressed this issue by arti®cially manipulating pH i in Arenicola marina using phenylphosphoric acid. If pH is lowered markedly below pH 7.0, a change as small as 0.05 pH unit can substantially inhibit PFK activity.…”

“…The point here is that, for acidi®cation of pH i change to have an inhibitory in¯uence on metabolic processes, it must be of suf®cient magnitude to reach the biologically sensitive range of the process in question. Juretschke & Kamp (1990) experimentally addressed this issue by arti®cially manipulating pH i in Arenicola marina using phenylphosphoric acid. Finally, it is appropriate to note that the speci®c location of a histidyl residue within a given protein (i.e.…”