The maintenance of shore-level size gradients in an intertidal snail (Littorina sitkana)

Summary The size of many intertidal animals varies with tidal height. These size gradients could be produced by growth or survival varying with tidal height, or by animals moving to a preferred tidal level. The body size of the snail, Littorina sitkana, increases steadily with tidal height in rocky high intertidal habitats of British Columbia. To determine how size gradients were maintained in L. sitkana, I quantified how growth, survival, and snail movement varied with tidal height. I studied populations of L. sitkana found on sheltered pebble beach and exposed basaltic shelf habitats. Mark-recapture studies and experimental transplants showed that growth could not have produced the size gradients because snail growth rates in both habitats were as fast or faster at low tidal levels (where the snails were the smallest) than at high tidal levels. However, survival rates were lowest at low tidal levels. On pebble beaches, this was due to size selective predation on large snails by the pile perch, Rhacochilus vacca. On basaltic shelves, heavy wave action at low tidal levels may have caused the poor survival rates. Transplanted snails moved homeward on pebble beaches, but not on basaltic shelves. Reduced survival rates at low tidal levels cause size gradients in both habitats, and snail movement helps to maintain size gradients on pebble beaches.     

Role of calcium ions in the regulation of intramitochondrial metabolism. Effects of Na+, Mg2+ and ruthenium red on the Ca2+-stimulated oxidation of oxoglutarate and on pyruvate dehydrogenase activity in intact rat heart mitochondria.

1. In uncoupled rat heart mitochondria, the kinetic parameters for oxoglutarate oxidation were very close to those found for oxoglutarate dehydrogenase activity in extracts of the mitochondria. In particular, Ca2+ greatly diminished the Km for oxoglutarate and the k0.5 value (concentration required for half-maximal effect) for this effect of Ca2+ was close to 1 microM. 2. In coupled rat heart mitochondria incubated with ADP, increases in the extramitochondrial concentration of Ca2+ greatly stimulated oxoglutarate oxidation at low concentrations of oxoglutarate, but not at saturating concentrations of oxoglutarate. The k0.5 value for the activation by extramitochondrial Ca2+ was about 20 nM. In the presence of either Mg2+ or Na+ this value was increased to about 90 nM, and in the presence of both to about 325 nM. 3. In coupled rat heart mitochondria incubated without ADP, increases in the extramitochondrial concentration of Ca2+ resulted in increases in the proportion of pyruvate dehydrogenase in its active non-phosphorylated form. The sensitivity to Ca2+ closely matched that found to affect oxoglutarate oxidation, and Mg2+ and Na+ gave similar effects. 4. Studies of others have indicated that the distribution of Ca2+ across the inner membrane of heart mitochondria is determined by a Ca2+-transporting system which is composed of a separate uptake component (inhibited by Mg2+ and Ruthenium Red) and an efflux component (stimulated by Na+). The present studies are entirely consistent with this view. They also indicate that the intramitochondrial concentration of Ca2+ within heart cells is probably about 2--3 times that in the cytoplasm, and thus the regulation of these intramitochondrial enzymes by Ca2+ is of likely physiological significance. It is suggested that the Ca2+-transporting system in heart mitochondria may be primarily concerned with the regulation of mitochondrial Ca2+ rather than cytoplasmic Ca2+; the possible role of Ca2+ as a mediator of the effects of hormones and neurotransmitters on mammalian mitochondrial oxidative metabolism is discussed.     

The activation of pyruvate dehydrogenase in the perfused rat heart by adrenaline and other inotropic agents.

Adrenaline resulted in a reversible 4-fold increase in the amount of pyruvate dehydrogenase in its active non-phosphorylated form in the perfused rat heart within 1 min. The increase was less in extent in hearts from starved or diabetic rats or in hearts from control rats oxidizing acetate, unless pyruvate was added to the perfusion medium. Increases could also be induced by other inotropic agents, supporting the hypothesis that increases in cytoplasmic Ca2+ can be relayed into mitochondria and influence oxidative metabolism.     

Sequencing, cloning, and expression of human red cell-type acid phosphatase, a cytoplasmic phosphotyrosyl protein phosphatase.

Low molecular weight phosphotyrosyl protein phosphatases of human placenta and human red cell were purified and sequenced by a combination of Edman degradation and tandem mass spectrometry. Screening of a human placental lambda gt11 cDNA library yielded overlapping cDNA clones coding for two distinct human cytoplasmic low molecular weight phosphotyrosyl protein phosphatases (HCPTPs). The two longest clones, designated HCPTP1-1 and HCPTP2-1, were found to have identical nucleotide sequences, with the exception of a 108-base pair segment in the middle of the open reading frame. Polymerase chain reaction studies with human genomic DNA suggest that the difference between HCPTP1-1 and HCPTP2-1 does not result from alternative RNA splicing. Studies with a human chromosome 2-specific library confirmed that these sequences are located on chromosome 2, which is known to be the location of red cell acid phosphatase locus ACP1. The coding sequences of HCPTP1-1 and HCPTP2-1 were placed downstream from a bacteriophage T7 promoter and the proteins were expressed in Escherichia coli. The resulting recombinant enzymes (designated HCPTP-A and HCPTP-B, respectively) showed molecular weights of 18,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and both of them exhibited immunoreactivity with antisera raised against authentic human placental and bovine heart enzymes. The expressed proteins were highly active towards the phosphatase substrates p-nitrophenyl phosphate, beta-naphthyl phosphate, and O-phospho-L-tyrosine, but not alpha-naphthyl phosphate, threonine phosphate, or O-phospho-L-serine. HCPTP-A and -B possessed effectively identical amino acid compositions, immunoreactivities, inhibition by formaldehyde, and kinetic properties when compared with two human red cell acid phosphatase isoenzymes. It is concluded that HCPTP-A and -B are the fast and slow forms of red cell acid phosphatase, respectively, and that this enzyme is not unique to the red cell but is instead expressed in all human tissues.     

The role of mitochondrial Ca2+ transport and matrix Ca2+ in signal transduction in mammalian tissues

The pyruvate, NAD(+)-isocitrate and 2-oxoglutarate dehydrogenases are key regulatory enzymes in intramitochondrial oxidative metabolism in mammalian tissues, and can all be activated by increases in Ca2+ in the micromolar range. There is now mounting evidence that hormones and other stimuli which act by increasing cytosolic Ca2+ also, as a result, cause increases in mitochondrial matrix Ca2+ and hence activation of these enzymes, suggesting that the primary physiological function of mitochondrial Ca2(+)-transport is to be involved in this relay mechanism. This may also explain how in such circumstances rates of ATP production may be increased to meet the greater demand, but without any decreases in ATP/ADP occurring.     

The effects of calcium ions and adenine nucleotides on the activity of pig heart 2-oxoglutarate dehydrogenase complex.

1. The effects of Ca2+ (mainly by using EGTA buffers), pH, ATP and ADP on the activity of the 2-oxoglutarate dehydrogenase complex from pig heart were explored. 2. Ca2+ (about 30 micrometer) resulted in a decrease in the apparent Km for 2-oxoglutarate from 2.1 to 0.16 mM (at pH 7) without altering the maximal velocity. At 0.1 mM-oxoglutarate there was a 4--5-fold activation by Ca2+, with an apparent Km for Ca2+ of 1.2 micrometer. A similar activation was also observed with Sr2+ (Km 15.1 micrometer), but not wised markedly from pH 7.4 TO 6.6. The effects of Ca2+ remained evident over this pH range. 4. In the presence of Mg2+, ATP resulted in a marked increase in the apparent Km for oxoglutarate, whereas ADP greatly decreased thisp arameter. The concentrations of adenine nucleotide required for half-maximal effects were about 10 micrometer in each case. 5. The effects of the adenine nucleotides and Ca2+ on the apparent Km for oxoglutarate appeared to be essentially independent of each other, reversible, and demonstrable in the presence of end product inhibition by NADH and obtained. 6. Effects similar to those described above were also observed on the activity of 2-oxoglutarate dehydrogenase from rat heart and brown adipose tissue. 7. We discuss the mechanisms controlling this enzyme's activity and compare these regulatory features with those of NAD-isocitrate dehydrogenase and the pyruvate dehydrogenase system, which are also sensitive to Ca2+ and adenine nucleotides.     

Abnormal dorsal light response in teleost fish after intraocular injection of 6-hydroxydopamine

Following unilateral intraocular injection with 6-hydroxydopamine to the right eye, Midas cichlids displayed an acute abnormal dorsal light response, in favour of the right eye. This condition was reversed immediately by dopamine or dopamine receptor agonists delivered by intraocular injection but this recovery was not sustained, Retinal dopamine production reappeared gradually from day 30 post-6-hydroxydopamine treatment, and coincided with the fish beginning to adopt a normal dorsal light reaction. Dopamine production recovered completely at day 45 post-6-hydroxydopamine injection and coincided with complete recovery of the normal dorsal light reaction. These observations suggest a role for intraocular dopamine in maintenance of the visual part of the normal dorsal light reaction.     

Rapid Copper Acquisition by Developing Murine Mesothelioma: Decreasing Bioavailable Copper Slows Tumor Growth,Normalizes Vessels and Promotes T Cell Infiltration

Copper, an essential trace element acquired through nutrition, is an important co-factor for pro-angiogenic factors including vascular endothelial growth factor (VEGF). Decreasing bioavailable copper has been used as an anti-angiogenic and anti-cancer strategy with promising results. However, the role of copper and its potential as a therapy in mesothelioma is not yet well understood. Therefore, we monitored copper levels in progressing murine mesothelioma tumors and analyzed the effects of lowering bioavailable copper. Copper levels in tumors and organs were assayed using atomic absorption spectrophotometry. Mesothelioma tumors rapidly sequestered copper at early stages of development, the copper was then dispersed throughout growing tumor tissues. These data imply that copper uptake may play an important role in early tumor development. Lowering bioavailable copper using the copper chelators, penicillamine, trientine or tetrathiomolybdate, slowed in vivo mesothelioma growth but did not provide any cures similar to using cisplatin chemotherapy or anti-VEGF receptor antibody therapy. The impact of copper lowering on tumor blood vessels and tumor infiltrating T cells was measured using flow cytometry and confocal microscopy. Copper lowering was associated with reduced tumor vessel diameter, reduced endothelial cell proliferation (reduced Ki67 expression) and lower surface ICAM/CD54 expression implying reduced endothelial cell activation, in a process similar to endothelial normalization. Copper lowering was also associated with a CD4⁺ T cell infiltrate. In conclusion, these data suggest copper lowering is a potentially useful anti-mesothelioma treatment strategy that slows tumor growth to provide a window of opportunity for inclusion of other treatment modalities to improve patient outcomes.