Inter-site variation in allometry and wood density of Goupia glabra Aubl. in Amazonia.

The present study aims to compare the allometry and wood density of Goupia glabra Aubl. (Goupiaceae) in two different terra-firme sites in Amazonian forest. A total of 65 trees ≥ 10 cm DBH was sampled in both sites, with 39 trees in Nova Olinda do Norte (NOlinda, near the Amazon River) and 29 trees in Apuí (near the southern edge of the Amazon forest). Except for the relationship between DBH (diameter at breast height) and Ht (total height), allometric relationships for G.glabra differed significantly between sites. Apuí had lower intercept and greater slope for log10 (DBH) versus log10 (Hs - stem height), and, conversely, greater intercept and lower slope for log10 (DBH) versus log10 (Ch - crown height). The slope differed significantly between the sites for DBH versus Cd (crown diameter), with greater slope found for NOlinda. Mean basic wood density in Apuí was 8.8% lower than in NOlinda. Our findings highlight the variation in adaptive strategy of G. glabra due to environmental differences between sites. This is probably because of different canopy-understory light gradients, which result in differentiation of resource allocation between vertical and horizontal growth, which, in turn, affects mechanical support related to wood density. We also hypothesize that differences in soil fertility and disturbance regimes between sites may act concomitantly with light.

Restoration of membrane potential in mitochondria deenergized with carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP).

The membrane potential (delta psi) of rat liver mitochondria dropped upon addition of carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) but was gradually and fully restored to the original value by the subsequent addition of dithioerythritol. Concomitantly, Ca2+ released from mitochondria was reaccumulated and the oxidative phosphorylation process completely recoupled. Neither of these effects has been observed with dinitro-o-cresol or 2,4-dinitrophenol, uncouplers which, unlike FCCP, do not react with thiols. Delta psi abolished by FCCP was also restored, though incompletely, by albumin; a prompt and complete restoration was however achieved upon subsequent addition of dithioerythritol. Dithioerythritol also completely and rapidly restored the delta psi decreased by addition of diazene dicarboxylic acid bisdimethylamide (diamide).

Studies on the transport of carnitine in the brain using synaptosomes isolated from guinea-pig cerebral cortex.

Synaptosomes isolated from guinea pig cerebral cortex accumulate L-carnitine from the medium in an active process, dependent on the sodium gradient across the plasma membrane and on (Na+ + K+)-ATPase activity. L-Carnitine uptake is inhibited by oxidative phosphorylation uncouplers and by ouabain, a known inhibitor of (Na+ + K+)-ATPase. In addition, the omission of Na+ or its replacement by Li+ inhibited the transport, which was also competitively inhibited by gamma-aminobutyrate. The kinetics of carnitine uptake show that the overall process would consist of two components: a passive diffusion and a carrier-mediated transport which is saturated at 1-2 mM carnitine concentration.

Spermine-mediated casein kinase II-uptake by rat liver mitochondria.

Spermine, ubiquitous intracellular polyamine, is able to promote the transmembrane translocation of casein kinase CKII through the outer membrane of rat liver mitochondria and its binding to more internal mitochondrial structures. These findings suggest that spermine may play a critical role in regulating the subcellular distribution of casein kinase CKII.

Uptake of spermine by rat liver mitochondria and its influence on the transport of phosphate.

Spermine, a polyamine present in the mammalian cells at rather high concentration, has, among other actions, a remarkable stabilizing effect on mitochondria, functions which have generally been attributed to the capability of this and other polyamines to bind to membrane anionic sites. In the present paper evidence is provided that at physiological concentrations spermine may also be transported into rat liver mitochondrial matrix space, provided that mitochondria are energized and inorganic phosphate is simultaneously transported. The close dependence of spermine transport is also demonstrated by the concurrent efflux of spermine and inorganic phosphate when mitochondria preloaded with the two ionic species are deenergized either with uncouplers or respiratory chain inhibitors. Furthermore, Mersalyl, the known inhibitor of phosphate transport, prevents both spermine uptake and release. Mg2+ inhibits the transport of spermine conceivably by competing for the some binding sites on the mitochondrial membrane. The physiological significance of these results is discussed.

Ca2+-mediated action of long-chain acyl-CoA on liver mitochondria energy-linked processes.

The decrease of steady-state transmembrane potential (delta psi) and loss of accumulated Ca2+ are magnified if palmitoyl-CoA is added to rat liver mitochondria exposed to Ca2+ and phosphate. The extent of this damage increases with increasing concentration of long-chain acyl-CoA. Addition of L-carnitine with or without the addition of palmitoyl-CoA considerably delays the deenergization. In the latter case, there is a substantial decrease in the assayed endogenous long-chain acyl-CoA content. This protective action of L-carnitine is abolished by L-aminocarnitine, a powerful inhibitor of carnitine palmitoyl transferase (palmitoyl-CoA: L-carnitine O-palmitoyltransferase, EC 2.3.1.21.). The removal of Ca2+ by EGTA, or the inhibition of its uptake by Ruthenium red or Mg2+ further enhances the degree of protection.

Metabolic changes induced by maximal exercise in human subjects following L-carnitine administration.

In double-blind cross-over experiments, ten moderately trained male subjects were submitted to two bouts of maximal cycle ergometer exercise separated by a 3 day interval. Each subject was randomly given either L-carnitine (2 g) or placebo orally 1 h before the beginning of each exercise session. At rest L-carnitine supplementation resulted in an increase of plasma-free carnitine without a change in acid-soluble carnitine esters. Treatment with L-carnitine induced a significant post-exercise decrease of plasma lactate and pyruvate and a concurrent increase of acetylcarnitine. The determination of the individual carnitine esters in urine collected for 24 h after the placebo exercise trial revealed a decrease of acetyl carnitine and a parallel increase of a C4 carnitine ester, probably isobutyrylcarnitine. Conversely, acetylcarnitine was strongly increased and C4 compounds were almost suppressed in the L-carnitine loading trial. These results suggest that L-carnitine administration prior to high-intensity exercise stimulates pyruvate dehydrogenase activity, thus diverting pyruvate from lactate to acetylcarnitine formation.

Mitochondrial alterations induced by aspirin in rat hepatocytes expressing mitochondrially targeted green fluorescent protein (mtGFP).

Mitochondria in primary living hepatocytes were visualized in cells transfected with a chimeric plasmid encoding for the green fluorescent protein (GFP) of Aequorea victoria engineered to be specifically targeted to mitochondria, as described recently (Rizutto et al. (1995) Curr. Biol. 5, 635-642). The identification of the fluorescent organelles as authentic mitochondria was confirmed by double labeling with rhodamine 123. Acetylsalicylate treatment of hepatocytes induced in mitochondria typical morphological alterations closely analogous to the swelling promoted by acetylsalicylate in isolated mitochondria. Cyclosporin A, which in isolated mitochondria prevents the changes induced by acetylsalicylate, had no protective action but induced per se specific alterations in the morphology of mitochondria. Moreover, exposure of hepatocytes to cyclosporin A followed by acetylsalicylate caused the same mitochondrial changes induced by each of the two compounds separately. The structural alterations caused by acetylsalicylate were constantly associated with a decrease in mitochondrial urea synthesis and cell viability.

Favorable effects of L-carnitine treatment on hypertriglyceridemia in hemodialysis patients: decisive role of low levels of high-density lipoprotein-cholesterol.

Twenty-nine hemodialyzed patients with hypertriglyceridemia were given L-carnitine (20 mg/kg iv at the end of each dialysis) for 120 days and then placebo for the same duration in order to evaluate the lipid-lowering effects of the metabolite. A dramatic reduction in triglyceride levels was observed only in the group of patients (n = 12) with high basal triglyceride values, low levels of high-density lipoprotein-cholesterol, and with apoprotein A at the lower limit of normal range. During L-carnitine treatment these patients exhibited significantly increased high-density lipoprotein-cholesterol and apoprotein A. No rebound effects were observed. L-Carnitine did not provoke changes in the lipid parameters in the group (n = 17) with high basal triglyceride values, and normal high-density lipoprotein-cholesterol and apoprotein A. Hematocrit values increased in all the 29 patients during L-carnitine treatment. At the end of the experimental protocol, L-carnitine dosage was increased to 60 mg/kg iv (at the end of each dialysis) in four patients of the group of nonresponders and prolonged for 60 days. This produced a considerable reduction in triglyceride levels. The above results suggest that L-carnitine can be effective in the management of hypertriglyceridemia in the hemodialyzed patient especially when low high-density lipoprotein-cholesterol levels are present.

The alterations in the energy linked properties induced in rat liver mitochondria by acetylsalicylate are prevented by cyclosporin A or Mg2+.

The alterations in rat liver mitochondria induced by acetylsalicylate in the presence of low concentrations of Ca2+ (large amplitude swelling, permeability to 14C]sucrose, collapse of transmembrane potential and effluxes of endogenous Mg2+ and accumulated Ca2+) were fully prevented by either cyclosporin A or Mg2+. Cyclosporin A and Mg2+ were also capable of restoring transmembrane potential upon its decrease induced by acetylsalicylate. The loss of endogenous Mg2+ was the primary effect promoted by acetylsalicylate; the other noxious effects followed. These results indicate that Mg2+ are fundamental components of the mitochondrial permeability barrier and that their loss might be responsible for the membrane transition induced by acetylsalicylate.

Protective action of methylglyoxal bis (guanylhydrazone) on the mitochondrial membrane.

At low concentrations (0.5-1.0 mM) methylglyoxal bis (guanylhydrazone) (MGBG) exhibited a clearcut protection of rat liver mitochondria against the deenergizing action of either Ca2+, or oxidizing agents (butylhydroperoxide and oxaloacetate). Such a protection resulted from the prevention of transmembrane potential decay, discharge of accumulated Ca2+, release of mitochondrial Mg2+, adenine nucleotides and pyridine nucleotides and mitochondrial swelling. At high concentrations (5-10 mM) MGBG induced functional alterations of mitochondria (decrease of transmembrane potential, lower capability to accumulate and to retain Ca2+) which can be reversed by resuspension of mitochondria in a MGBG free medium. These reversible mitochondrial alterations by high MGBG concentrations are interpreted as a consequence of an aggregation and coprecipitation of suspended mitochondria.

L-carnitine effect on halothane-treated mitochondria.

Addition of halothane to the incubation medium is shown to lower respiratory control and transmembrane potential and to increase ATPase activity in isolated rat liver mitochondria. Evidence is presented that L-carnitine is able to substantially decrease the negative effects of halothane on the energy-linked processes of mitochondria. The effects of halothane and the protective action of L-carnitine are discussed in the light of a possible involvement of long-chain acyl CoA in the unpairing of mitochondrial energy-linked functions.

Carnitine: metabolism and clinical chemistry.

In man carnitine is synthesized from proteic trimethyllysine in liver, brain and kidney. Muscles which contain approximately 98% of carnitine must take it up from the blood in an exchange process with endogenous deoxycarnitine, the immediate precursor of carnitine. Uneven organ distribution of the enzymes catalyzing carnitine synthesis further implies an inter-organ transport of the intermediates. Assay of these intermediates in blood may assist causal definition of carnitine deficiency syndromes. Besides catalyzing the transport of long-chain acyls in mitochondria, carnitine is necessary for the export of intra-mitochondrially produced short-chain acyls and for trapping and elimination of unphysiological acyls (benzoic, pivalic, valproic acids etc.). Unlike the corresponding acyl-CoA, carnitine esters are capable of diffusing across cellular membranes, and may be eliminated in urine, distributed in tissues or both. Assay of physiological and unphysiological carnitine esters in urine is necessary for the diagnosis of carnitine insufficiencies.

Carnitine transport in rat heart slices: I. The action of thiol reagents on the acetylcarnitine/carnitine exchange.

Rat heart slices show a permeability barrier that can be crossed by carnitine but not by sucrose and inulin. The integrity of thiol groups of heart cell membrane is essential for the uptake of carnitine. N-ethylmaleimide inhibits the transport into heart slices which is insensitive to Mersalyl. On the contrary both N-ethylmaleimide and Mersalyl inhibit acetyl carnitine/carnitine exchange. The amount of thiol groups titrated by the above reagents are related to the extent of exchange inhibition.

On the transport mechanisms of carnitine and its derivative in rat heart slices.

The transport of L-carnitine and analogs in exchange with previously loaded 3H-carnitine has been studied in heart tissue slices. The slices are first loaded with 3H-carnitine; then they are transferred in vessels containing the same medium with possible exchangers. Acetylcarnitine, L-carnitine, D-carnitine and deoxycarnitine exchange with internal 3H-carnitine. The exchange with acetylcarnitine, the largest among the compounds tested, appears to be a saturation process and is not affected either by oxidative phosphorylation and glycolysis inhibitors. The exchange of external acetylcarnitine with internal carnitine support that also in vivo heart tissue can utilize acetylcarnitine present in blood. Finally the observed deoxycarnitine/carnitine exchange, occurring in the reverse direction, may be the mechanism by which the heart accumulate external carnitine in exchange with endogenous deoxycarnitine.

On the biochemical significance of phosphoserine: a working hypothesis.

The significance of the presence of free phosphoserine in living cells represents an intriguing problem. Its utilization for the synthesis of phosphoproteins and phospholipids has been ruled out. It is produced extensively by hydrolysis of phosphoproteins or phosphatidylserine since no phosphorylating enzyme for serine is present. So far the only significance of phosphoserine has been related to its participation in the exchange reaction with serine, the meaning of which is quite unclear. Evidence is presented that phosphoserine could modulate the activity of phospholipase A2, thus regulating the permeability properties of cellular and intracellular membranes which depend largely on phospholipase pattern. Phosphoserine in fact inhibits in a competitive way phospholipase A2 from cobra venom.

Carnitine transport in rat heart slices: II. The carnitine/deoxycarnitine antiport.

In rat heart slices carnitine transport occurs in an exchange process with deoxycarnitine. This has been demonstrated in double labelling experiments allowing a preloading of either 3H-carnitine or 14C-deoxycarnitine, the immediated precursor of carnitine. The stoichiometry of the carnitine/deoxycarnitine exchange resulted close to one in both directions. The relative kinetics supports the assumption that the process is mediated by a membrane bound protein. The results may rationalize the circumstance that carnitine is taken up by myocardium against a concentration gradient. The meaning of the carnitine/deoxycarnitine exchange is discussed.

Carnitine effect on heart steatosis induced in rats by rapeseed oil.

Myocardial triglyceride levels in rats fed a high erucic acid rapeseed oil diet for three days were five times higher than in controls. The incorporation of erucic acid and, to a lower extent, some unsaturated fatty acids was increased, as well as total cholesterol content, compared to controls. The presence of 5% carnitine in the diet partially prevented these effects. It is assumed that carnitine may be a rate limiting factor in the myocardial catabolism of unsaturated fatty acids and particularly erucic acid, when these substance are ingested in supraoptimal amount.

Effect of physical training on carnitine concentration in liver, heart and gastrocnemius muscle of rat.

Physical training by compulsed swimming induces in rat heart a significant increase in the concentrations of carnitine and free carnitine but no detectable changes in liver and gastrocnemius muscle are observed. These results are consistent with the increased utilisation of fatty acid and pyruvate in trained animals and with an enhanced demand for carnitine by heart muscle.

Pantethine and pantothenate effect on the CoA content of rat liver.

The role of pantethine as a precursor of CoA in rat liver has been examined. It has been demonstrated that pantethine induces a significant increase in the total CoA content both in perfused liver and in liver homogenate, while it fails to affect the mitochondrial CoA content when added to isolated mitochondria. Pantethine is more efficient than pantothenate in inducing the synthesis of CoA in rat liver, even in the presence of added cysteine. The possible metabolic implications are discussed.