Tissue channel morphology in Octopus

Summary The morphology of tissue channels in muscle and neural tissues of Octopus was investigated, at the ultrastructural level, with a technique involving the precipitation of ferrocyanide ions. The numbers, sizes and conductivities of the channels were estimated from quantitative data. No evidence was gained to indicate that the low microvascular density in Octopus is coupled to an especially extensive network of extravascular channels. The tissue channel system in Octopus appears to be broadly comparable with the mammalian system; a lack of information prevents more appropriate comparisons with marine fishes. Probable functions of tissue channels in Octopus and mammals, and reasons for apparent similarities and differences in the channel organization of these divergent groups, are discussed.     

Association-dissociation equilibria of Octopus hemocyanin

The equilibria between the native (decameric) Octopus hemocyanin and its subunits were studied by analytical sedimentation. Equilibrium is obtained slowly, but the reaction is thermodynamically reversible. The mass action law for a monomer-decamer reaction is obeyed. The reassociated hemocyanin is virtually identical in its sedimentation behavior and oxygen binding with the native protein. The association-dissociation equilibria are mediated by cations; Mg2+, Ca2+, Na+, and H+ are all effective in stabilizing the decameric form at appropriate concentrations. About three to four cations per monomer must be bound for association to occur. Under some conditions, dimers of the subunits can be observed, but formation of this dimer does not depend on cation concentration, and it does not appear to be an obligate intermediate in the association to decamer.     

D-lactate metabolism in starved Octopus ocellatus

The concentrations of D- and L-lactate, methylglyoxal and pyruvate were measured in tissues of normal and starved Octopus ocellatus. D-Lactate was always more abundant than L-lactate in the tissues. D-Lactate, pyruvate and methylglyoxal were present in 320, 94 and 43 times higher concentrations in tentacle of O. ocellatus of control group than those in normal rat skeletal muscle. The D-lactate concentration in the tentacle of O. ocellatus was 17-fold higher than that in Octopus vulgars. The activities of enzymes involved with D-lactate metabolism such as pyruvate kinase, octopine dehydrogenase, glyoxalase I and II and lactate dehydrogenase were measured in those tissues. The activities of glyoxalase I and II, and D-lactate dehydrogenase were increased in mantle and tentacle of starved octopus, while the levels of D-lactate and related metabolites were lowered in these tissues. The experimental results presented in this report and up to the present indicate that D-lactate is actively used for energy production in the tentacle and mantle of the starved animals. In octopus, especially starved octopus D-lactate was actively produced from methylglyoxal, which is formed via aminoacetone from threonine and glycine.     

Neuropeptidergic control of Octopus oviducal gland

The oviducal gland of the female of Octopus vulgaris lies about halfway along the oviduct. Progesterone and 17beta-estradiol receptors have been immunolocalized in the nuclei of the cells of the glandular compartment of previtellogenic glands. We also have evidence of FMRFamide-like and cGnRH-I-like immunoreactivity in the nerve endings that reach the oviducal gland. Moreover, we have recently shown APGWamide immunoreactivity in the glandular cells of the inner part of the oviducal gland. Here we report a review on these findings as well as our latest studies on the effect that neuropeptides may exert on the secretory activity of the oviducal gland. cAMP seems to be a possible second messenger involved in such a process. We discuss the findings of a neuropeptidergic action on the glandular cells of oviducal gland in a more complex frame of molecules, such as steroids, biogenic amines and neuromodulators, controlling the activity of the gland.     

Monooxygenase activity of Octopus vulgaris hemocyanin

Octopus vulgaris hemocyanin ( Ov-Hc) and one of its minimal functional units ( Ov-g) have been purified, and their spectroscopic features and monooxygenase (phenolase) activity have been examined in detail. The oxy forms of both Ov-Hc and Ov-g are stable in 0.5 M borate buffer (pH 9.0) even in the presence of a high concentration of urea at 25 degrees C; approximately 90 and approximately 75% of the (mu-eta (2):eta (2)-peroxo)dicopper(II) species of Ov-Hc and Ov-g, respectively, remained unchanged after argon (Ar) gas flushing of the sample solutions for 1 h. The catalytic activity of Ov-g in the oxygenation reaction (multiturnover reaction) of 4-methylphenol ( p-cresol) to 4-methyl-1,2-dihydroxybenzene (4-methylcatechol) was higher than that of Ov-Hc, and its catalytic activity was further accelerated by the addition of urea. Kinetic deuterium isotope effect analysis and Hammett analysis using a series of phenol derivatives under anaerobic conditions (single-turnover reaction) have indicated that the monooxygenation reaction of phenols to catechols by the peroxo species of oxyhemocyanin proceeds via electrophilic aromatic substitution mechanism as in the case of tyrosinase. The effect of urea on the redox functions of oxyhemocyanin is discussed on the basis of the spectroscopic analysis and reactivity studies.     

Oxygen equilibria of Octopus dofleini hemocyanin

Oxygen binding by Octopus dofleini hemocyanin was examined under very nearly physiological conditions. The effects of pH, ionic composition, temperature, and aggregation were controlled so that the role each plays in modulating oxygen binding can be isolated. There is a very large effect of pH on affinity, the Bohr effect (delta log P50/delta pH = -1.7), which is the same at 10 and 20 degrees C. However, cooperativity is substantially altered over the same range of pHs at the two temperatures. The allosteric properties were examined by comparing the experimental data points to curves generated by use of the Monod-Wyman-Changeux model. A computer-fitting process was developed which allowed the individual allosteric parameters to be varied independently until the best fit could be determined. The relationship between kR and kT is responsible for the effect of pH on cooperativity. A change in the allosteric properties of the T form is primarily responsible for the differences due to temperature. Changing cation concentrations when the molecule is in the fully aggregated 51S form alters affinity without influencing cooperativity. The effect of Mg2+ is much greater than that of Na+. If the 51S decamer is dissociated to 11S monomers by removing divalent cations, oxygen binding is noncooperative. There is evidence for negative cooperativity, indicating heterogeneity of function within the subunit which contains seven oxygen binding domains. Association into decamers generates conformational change which results in a much wider range of allosteric function.     

Malabsorption syndrome observed in the common octopus Octopus vulgaris infected with Aggregata octopiana (Protista: Apicomplexa)

Octopus vulgaris infected with Aggregata octopiana were collected from an open-water culture system in the Ría of Aldán (NW Spain). Digestive tract infection values were determined with the use of a Neubauer chamber by counting the number of A. octopiana sporocysts. After determining enzyme activity values by the colorimetric Api-Zym system Biomerieux, one representative enzyme of glycosidases, peptid hydrolases and phosphoric hydrolases showing high activity was spectrophotometrically analysed. The enzymes were maltase and leucine-aminopeptidase (LAP) involved in the absorption process, and acid phosphatase, a lysosomic enzyme, respectively. Enzymatic activity of maltase and LAP decreased significantly, with increased sporocyst counts. However, acid phosphatase activity increased with severity of infection, indicating the presence of degradative enzymes from phagocytic cells in the infected area. A detrimental effect on gastrointestinal function may result from a decrease or malfunction of absorption enzymes. The results suggest a malabsorption syndrome resulting from parasitic infection.     

Developing Skin Analogues for a Robotic Octopus

In order to fabricate a biomimetic skin for an octopus inspired robot,a new process was developed based on mechanical properties measured from real octopus skin.Various knitted nylon textiles were tested and the one of 10-denier nylon was chosen as reinforcement.A combination of Ecoflex 0030 and 0010 silicone rubbers was used as matrix of the composite to obtain the right stiffness for the skin-analogue system.The open mould fabrication process developed allows air bubble to escape easily and the artificial skin produced was thin and waterproof.Material properties of the biomimetic skin were characterised using static tensile and instrumented scissors cutting tests.The Young's moduli of the artificial skin are 0.08 MPa and 0.13 MPa in the longitudinal and transverse directions,which are much lower than those of the octopus skin.The strength and fracture toughness of the artificial skin,on the other hand are higher than those of real octopus skins.Conically-shaped skin prototypes to be used to cover the robotic arm unit were manufactured and tested.The biomimetic skin prototype was stiff enough to maintain it conical shape when filled with water.The driving force for elongation was reduced significantly compared with previous prototypes.