Lipid Metabolism in the Brown Marine Algae Fucus vesiculosus and Ascophyllum nodosum

Lipid metabolism and environmental effects on this process havebeen studied in the marine brown algae Fucus vesiculosus andAscophyllum nodosum. These algae showed very similar patternsof lipid metabolism during 24 h incubations. Labelling from[1-¹⁴C]acetate showed the major labelled lipids to be the ß-alanineether lipid and the neutral lipid fraction in both algae. Ofthe glycolipids, only sulphoquinovosyldiacylglycerol was welllabelled and the phosphoglycerides were all poorly labelled.The major labelled fatty acids were palmitate and oleate, againin both algae, although Fucus vesiculosus also showed significantlabelling of stearate and behenate. Although the amount of fattyacid labelling increased with time, the proportion of labelin palmitate and oleate remained approximately constant. Verylong chain fatty acids (arachidic, behenic) were increasinglylabelled with time. Lowered incubation temperatures decreased labelling of the saturatedfatty acids. Cu²⁺ increased the proportion of oleate labelledin both algae, and of linoleate in Fucus vesiculosus. This cationdecreased the percentage labelling of stearate and myristatein Ascophyllum nodosum. Lipid metabolism in Ascophyllum nodosumwas more sensitive to raised Cu²⁺ levels than in Fucus vesiculosus Key words: Acyl lipid metabolism, Fucus vesiculosus, temperature effects, Ascophyllum nodosum, copper pollution     

The oxidation and utilization of palmitate, stearate, oleate and acetate by the mammary gland of the fed goat in relation to their overall metabolism, and the role of plasma phospholipids and neutral lipids in milk-fat synthesis

1. Measurements were made of milk yield, mammary blood flow and arteriovenous differences of each plasma lipid fraction, and their specific radioactivities, during the infusion of [U-¹⁴C]stearate, [U-¹⁴C]oleate, [U-¹⁴C]palmitate and [1-¹⁴C]acetate into fed lactating goats. 2. Entry rates of fatty acids into the circulation were 4·2mg./min./kg. body wt. for acetate, and 0·18, 0·28 and 0·42mg./min./kg. for stearate, oleate and palmitate respectively. Acetate accounted for 23% of the total carbon dioxide produced by the whole animal, and contributed to the oxidative metabolism of the mammary gland to about the same extent. Corresponding values for each of the long-chain acids were less than 1%. 3. There were no significant arteriovenous differences of phospholipids, sterols or sterol esters, and their fatty acid composition showed no net changes during passage through the mammary gland. 4. There were large arteriovenous differences of plasma triglycerides, and their fatty acid composition showed marked changes across the gland. The proportions of palmitate and stearate fell, and that of oleate increased. 5. Arteriovenous differences of plasma free fatty acids (FFA) were small and variable, but a large fall in the specific radioactivity of each of the long-chain acids examined indicated substantial uptake of plasma FFA, accompanied by roughly equivalent FFA release from mammary tissue. The uptake of FFA was confirmed by the extensive transfer of radioactivity into milk. The FFA of milk were similar in composition and radioactivity to the milk triglyceride fatty acids, and quite unlike plasma FFA. 6. The formation of large amounts of oleic acid (18–21 mg./min.) from stearic acid was demonstrated. 7. During the terminal stages of the [¹⁴C]acetate infusion, milk triglyceride fatty acids of chain length C₄–C₁₄ showed specific radioactivities that were 75–90% of that of blood acetate, and that of palmitate was roughly one-quarter of this value. Oleate and stearate were unlabelled. 8. The results confirmed that milk fatty acids of chain length C₄–C₁₄ arise largely from blood acetate, and palmitate is derived partly from acetate and partly from plasma triglyceride, the latter fraction being almost the sole precursor of oleate and stearate.     

Biosynthesis of Acyl Moieties of Capsaicin and its Analogues from Valine and Leucine in Capsicum Fruits

Biosynthetic pathways of acyl moieties of capsaicinoid in intactCapsicum fruits and spheroplasts prepared from placentas ofCapsicum fruits were examined using a radioisotopic technique.In intact Capsicum fruits, L-[U-¹⁴C] valine was incorporatedinto capsaicin and dihydrocapsaicin, the acyl constituents ofwhich are even-number branched chain fatty acids, while L-[U-¹⁴C]leucine was incorporated into nordihydrocapsaicin and homodihydrocapsaicin,which have odd-number branched chain facty acids as the acylmoieties. The intermediates of the odd- and even-number branchedchain fatty acids were identified with GLC/GPC after the spheroplastshad been incubated with L-[U-¹⁴C] valine or L-[U-¹⁴C] leucine.After incubation with L-[U-¹⁴C] valine, isobutyric acid and8-methyl nonanoic acid were detected, while isopentanoic acidand 9-methyl decanoic acid were found after incubation withL-[U-¹⁴C] leucine. The involvement of a-ketoisovalerate or a-ketoisocaproatein the biosynthesis of acyl moieties of capsaicinoid was alsodemonstrated in vitro using cell-free extracts of the placentasof Capsicum fruits. These findings suggest that the acyl moietiesof individual capsaicinoids in Capsicum fruits are synthesizedby pathways similar to those proposed for adipose tissue andbacteria. ¹Formation and Metabolism of Pungent Principle of Capsicum Fruits.Part IX. (Received September 2, 1980; Accepted November 17, 1980)     

Contraction-induced increase in Vmax of palmitate uptake and oxidation in perfused skeletal muscle

To evaluate the effects of contractions on thekinetics of uptake and oxidation of palmitate in a physiological musclepreparation, rat hindquarters were perfused with glucose (6 mmol/l),albumin-bound [1-¹⁴C]palmitate, andvarying amounts of albumin-bound palmitate (200-2,200 µmol/l) atrest and during muscle contractions. When plotted against the unboundpalmitate concentration, palmitate uptake and oxidation displayedsimple Michaelis-Menten kinetics with estimated maximal velocity(V_max)and Michaelis-Menten constant(K_m) values of42.8 ± 3.8 (SE)nmol · min¹ · g¹and 13.4 ± 3.4 nmol/l for palmitate uptake and 3.8 ± 0.4 nmol · min¹ · g¹and 8.1 ± 2.9 nmol/l for palmitate oxidation, respectively, at rest.Whereas muscle contractions increased theV_maxfor both palmitate uptake and oxidation to 91.6 ± 10.1 and 16.5 ± 2.3 nmol · min¹ · g¹,respectively, theK_m remainedunchanged.V_maxand K_m estimates obtained from Hanes-Woolf plots (substrate concentration/velocity vs.substrate concentration) were not significantly different. In theresting perfused hindquarter, an increase in palmitate delivery from31.9 ± 0.9 to 48.7 ± 1.2 µmol · g¹ · h¹by increasing perfusate flow was associated with a decrease in thefractional uptake of palmitate so that the rates of uptake andoxidation of palmitate remained unchanged. It is concluded that therates of uptake and oxidation of long-chain fatty acids (LCFA) saturatewith an increase in the concentration of unbound LCFA in perfusedskeletal muscle and that muscle contractions, but not an increase inplasma flow, increase theV_maxfor LCFA uptake and oxidation. The data are consistent with the notion that uptake of LCFA in muscle may be mediated in part by a transport system.

     

Radiolabelling Studies on the Lipid Metabolism in the Marine Brown Alga Dictyopteris membranacea

The lipid metabolism of the marine brown alga D. membranaceawas investigated using [2–¹⁴C]acetate, [1–¹⁴C]myristate,[l–^I4C]oleate and [l–¹⁴C]arachidonate as precursors.On incubation with [2–¹⁴C]acetate, 18:1 and 16:0 werethe main products formed by de novo synthesis and incorporatedinto polar lipids. With all the exogenous substrates used, DGTAwas strongly labelled and the subsequent rapid turnover of radioactivitysuggested a key role for this lipid in the redistribution ofacyl chains and most likely also in the biosynthesis of theeukaryotic galacto-lipids produced in the absence of PC. Inthe glycolipids a continuous accumulation of radioactivity wasobserved with all the substrates used. The labelling kineticsof molecular species of MGDG suggested the desaturation of 18:1to 18:4 and of 20:4 (n-6) to 20:5 (n–3) acids on thislipid. Both PG and PE were primary acceptors of de novo synthesizedfatty acids and exogenous [l–¹⁴C]oleate, but no evidenceexists for a further processing of acyl chains on these lipids.TAG, although strongly labelled with all exogenous [l–¹⁴CJacids,was not labelled when [2–¹⁴C]acetate was used as a precursorindicating the flux of endogenous fatty acids to be differentof that of exogenously supplied fatty acids. (Received November 4, 1997; Accepted February 23, 1998)     

Differences in partitioning of meal fatty acids into blood lipid fractions: a comparison of linoleate, oleate, and palmitate

There has been much interest in the health effects of dietary fat, but few studies have comprehensively compared the acute metabolic fate of specific fatty acids in vivo. We hypothesized that different classes of fatty acids would be variably partitioned in metabolic pathways and that this would become evident over 24 h. We traced the fate of fatty acids using equal amounts of [U-(13)C]linoleate, [U-(13)C]oleate, and [U-(13)C]palmitate given in a test breakfast meal in 12 healthy subjects. There was a tendency for differences in the concentrations of the tracers in plasma chylomicron-triacylglycerol (TG) (oleate > palmitate > linoleate). This pattern remained in plasma nonesterified fatty acid (NEFA) and very low-density lipoprotein (VLDL)-TG (P 相似文献   

Cooperative Pathway for Lipid Biosynthesis in Young Pea Leaves: Oleate Exportation from Chloroplasts and Subsequent Integration into Complex Lipids of Added Microsomes

In vitro [1-¹⁴C]-acetate incorporation into pea chloroplastlipids resulted in the synthesis of palmitic and oleic acids.Separation of chloroplasts after the incorporation proved thespecific exportation of [¹⁴C]-oleate towards the external medium.The addition of microsomes resulted in a stimulated exportationand integration of the exported oleate into the phosphatidylcholine(PC). In such experiments, the galactolipids were labelled byboth palmitate and oleate and confirmed the intraplastidialorigin of the fatty acids they incorporated. Isolated chloroplastsalone performed an acylation of PC by labelled oleate. The chloroplasticlocalization of this activity is discussed. (Received August 13, 1981; Accepted November 16, 1981)     

Acyl-CoA Synthetase in Maturing Safflower Seeds

Acyl-CoA synthetase in maturing seeds of safflower (Carthamustinctorius) was membranebound, and the highest specific activitywas associated with microsomes. Activity absolutely dependedon the concentrations of fatty acid, CoA, ATP and Mg²⁺. Theapparent K_m values were 4.2 µM for oleate, 24 µMfor CoA, and 250 µM for ATP. The optimum pH of the reactionwas 7.5. Triacsin C, a potent inhibitor of the animal and bacterialacyl-CoA synthetase, was ineffective for the safflower enzyme.The enzyme utilized C₁₆ and C₁₈ long-chain fatty acids preferentially,while medium-chain and very-long-chain fatty acids were poorsubstrates. The order of specificity for native fatty acidswas linoleate > oleate=palmitate > stearate. Althoughactivity per seed varied during seed maturation, it was enoughto account for the rate of triacylglycerol synthesis in vivo. (Received February 2, 1993; Accepted March 3, 1993)     

Respective oxidation of 13C-labeled lactate and glucose ingested simultaneously during exercise

Péronnet, F., Y. Burelle, D. Massicotte, C. Lavoie,and C. Hillaire-Marcel. Respective oxidation of¹³C-labeled lactate and glucoseingested simultaneously during exercise. J. Appl.Physiol. 82(2): 440-446, 1997.The purpose ofthis experiment was to measure, by using¹³C labeling, the oxidation rateof exogenous lactate (25 g, as Na⁺,K⁺,Ca²⁺, andMg²⁺ salts) and glucose (75 g)ingested simultaneously (in 1,000 ml of water) during prolongedexercise (120 min, 65 ± 3% maximum oxygen uptake in 6 male subjects). The percentage of exogenous glucose and lactateoxidized were similar (48 ± 3 vs. 45 ± 5%, respectively). However, because of the small amount of oral lactate that could be tolerated without gastrointestinal discomfort, the amountof exogenous lactate oxidized was much smaller than that of exogenousglucose (11.1 ± 0.5 vs. 36.3 ± 1.3 g, respectively) andcontributed to only 2.6 ± 0.4% of the energy yield(vs. 8.4 ± 1.9% for exogenous glucose). The cumulative amount ofexogenous glucose and lactate oxidized was similar to that observedwhen 100 g of[¹³C]glucose wereingested (47.3 ± 1.8 vs. 50.9 ± 1.2 g, respectively). When[¹³C]glucose wasingested, changes in the plasma glucose¹³C/¹²Cratio indicated that between 39 and 61% of plasma glucose derived fromexogenous glucose. On the other hand, the plasma glucose ¹³C/¹²Cratio remained unchanged when[¹³C]lactate wasingested, suggesting no prior conversion into glucose before oxidation.

     

Mobilization of Reserves and Synthesis of Sterols and Triterpenes in Seedlings of Two Canarian Euphorbia Species

Seedlings from Euphorbia canariensis and Euphorbia lambii weregrown in the dark at 25 °C. Protein and triglyceride contentas well as levels of sugars and amino acids in the endospermwere determined during endosperm depletion. In the endospermof Euphorbia canariensis, relatively low levels of amino acids(up to 1 µmol.endosperm^–1) were found of which glutamine/glutamateaccounted for 40% at the stage of radicle emergence. High levelsof amino acids (up to 4 µmol.endosperm^–1) comparedwith sugars (up to 2 µmol sucrose.endosperm^–1) weredetected in the endosperm of Euphorbia lambii. Arginine wasthe main component (28 µmol%) of the amino acids in thistissue. In both species amino acid composition changed graduallyduring endosperm depletion. Cotyledons retained their ability to absorb a variety of watersoluble substrates after removal of the endosperm. ¹⁴C from[U-¹⁴C]sucrose was effectively incorporated into the triterpenesof the laticifers and to a lesser extent into the sterols ofthe seedling. The highest incorporation values were found inyoung seedlings about 2 d after the emergence of the radicle.Seedlings of this age also showed high incorporation rates of¹⁴C from labelled alanine, serine, threonine, valine, leucineand isoleucine into both triterpenols and sterols, but no generalconclusions about metabolic channelling in lipid synthesis couldbe made. Endosperm, Euphorbia canariensis L. Euphorbia lambii Svent., sterols, triterpenols, amino acids, laticifer, biosynthesis     

Glycerolipid Synthesis in Avena Leaves during Greening of Etiolated Seedlings IV. Effect of Light on Fatty Acid Desaturation

Etiolated Avena sativa L. leaves were fed with [l-¹⁴C]acetatefor 20 h in the dark and labeled fatty acids in glycerolipidswere chased during 24 h in the light (greening condition) orin the dark, to determine the light effect on the fatty aciddesaturation. Oleate decrease in phosphatidylcholine was thesame in the light and in the dark, showing that oleate desaturationis independent of light (or greening). Linoleate desaturationin galactolipids, especially in monogalactosyl diacylglycerol,was enhanced by light and palmitate desaturation to hexadecenoatein phosphatidylglycerol was strictly light-dependent. (Received May 11, 1983; Accepted August 16, 1983)     

Formation of L-(+)-Tartaric Acid in Leaves of the Bean, Phaseolus vulgaris L.: Radioisotopic Studies with Putative Precursors

The biosynthetic pathway from D-glucose to L-(+)-tartaric acid(TA) in detached leaves of the bean, Phaseolus vulgaris L.,was studied in three cultivars, two of which were known to containTA and one of which lacked TA, with the aid of several putativeradiolabeled intermediates, namely D-[l-¹⁴C]glucose, D-[6-¹⁴C]glucose,D-[U-¹⁴C]glucose, D-[U-¹⁴C]gluconate, L-[U-¹⁴C]-ascorbic acid,L-[l-^l4C]idonate, D-xylo-5-[U-¹⁴C]hexulosonate, D-xylo-5-[l-¹⁴C]hexulosonate,D-xylo-5-[6-^l4C]hexulosonate and L-[U-^l4C]threonate. D-[U-¹⁴C]Glucoseand D-[U-^l4C]gluconate were converted to TA with low isotopicyield but this yield was further reduced when leaf tissues weresupplied with unlabeled D-gluconate or D-xylo-5-hexulosonate.D-xylo-5-[U-¹⁴C]Hexulosonate and D-xylo-5-[l-¹⁴C]hexulosonatewere good precursors of TA. D-xylo-5-[6-¹⁴C]Hexulosonate didnot furnish ¹⁴C to TA. Addition of a metabolic product of D-xylo-5-hexulosonate(which was labeled by D-xylo-5-[l-¹⁴C]hexulosonate but not byD-xylo-5-[6-¹⁴C]hexulosonate) to leaves labeled with D-xylo-5-[l-¹⁴C]hexulosonatedoubled the incorporation of ¹⁴C into TA. L-[U-¹⁴C]Ascorbicacid, L-[l-¹⁴C]idonate and L-[U-¹⁴C]threonate failed to producelabeled TA. A metabolic scheme to accommodate these observationsis presented. (Received October 21, 1988; Accepted March 29, 1989)     

The Metabolism of Abscisic Acid

The light-catalysed isomerization of (+)-abscisic acid (ABA)to its trans isomer during isolation from leaves was monitoredby the addition of (±)-[2-¹⁴C]ABA to the extraction medium.(+)Trans-abscisic acid (t-ABA) was found to occur naturallyin rose (Rosa arvensis) leaves at 20µg/kg fresh weight;(+)-ABA was present at 594µg/kg. (±)-[2-¹⁴D]Trans-abscisicacid was not isomerized enzymically to ABA in tomato shoots. (±)-Abscisic acid was converted by tomato shoots to awater-soluble neutral product, ‘Metabolite B’, whichwas identified as abscisyl-ß-D-glucopyranoside. When(±)-[2-¹⁴C]trans-abscisic acid in an equimolar mixturewith (±)-[2-¹⁴C}ABA was fed to tomato shoots it was convertedto its glucose ester 10 times faster than was ABA. Trans-abscisyl-ß-D-glucopyrano8ide only was formedfrom (±)-[2-¹⁴C]t-ABA in experiments lasting up to 30h. Glucosyl abscisate was formed slowly from ABA and the freeacid fraction contained an excess of the unnatural (–).ABAas did the ABA released from abscisyl-ß-D-glucopyranosideby alkaline hydrolysis. The (+).ABA appeared to be the solesource of the acidic ‘Metabolite C" previously noted. The concentrations of endogenous (+)-, (+)-[2-¹⁴C]-, and (–)-[2-¹⁴C]ABAremaining as free acid, and also in the hydrolysate of abscisyl-ß-D-glucopyranoside,were measured by the ORD, UV absorption, and scintillation spectrometryof highly purified extracts of ABA from tomato shoots whichhad been supplied with racemic [2-^l4C]ABA.     

Microdialysis ethanol removal reflects probe recovery rather than local blood flow in skeletal muscle

The present study compared the microdialysis ethanoloutflow-inflow technique for estimating blood flow (BF) in skeletalmuscle of humans with measurements by Doppler ultrasound of femoralartery inflow to the limb(BF_FA). The microdialysis probeswere inserted in the vastus lateralis muscle and perfused with a Ringeracetate solution containing ethanol,[2-³H]adenosine (Ado),andD-[¹⁴C(U)]glucose.BF_FA at rest increased from0.16 ± 0.02 to 1.80 ± 0.26 and 4.86 ± 0.53 l/minwith femoral artery infusion of Ado (Ado_FA,i) at 125 and 1,000 µg · min¹ · l¹thigh volume (low dose and high dose, respectively;P < 0.05) and to 3.79 ± 0.37 and6.13 ± 0.65 l/min during one-legged, dynamic, thigh muscle exercisewithout and with high Ado_FA,i,respectively (P < 0.05). The ethanoloutflow-to-inflow ratio (38.3 ± 2.3%) and the probe recoveries(PR) for [2-³H]Ado(35.4 ± 1.6%) and forD-[¹⁴C(U)]glucose(15.9 ± 1.1%) did not change withAdo_FA,i at rest (P = not significant). During exercisewithout and with Ado_FA,i, theethanol outflow-to-inflow ratio decreased(P < 0.05) to a similar level of17.5 ± 3.4 and 20.6 ± 3.2%, respectively(P = not significant), respectively,while the PR increased (P < 0.05) toa similar level (P = not significant)of 55.8 ± 2.8 and 61.2 ± 2.5% for[2-³H]Ado and to 42.8 ± 3.9 and 45.2 ± 5.1% forD-[¹⁴C(U)]glucose.Whereas the ethanol outflow-to-inflow ratio and PR correlated inverselyand positively, respectively, to the changes in BF during muscularcontractions, neither of the ratio nor PR correlated tothe Ado_FA,i-induced BF increase.Thus the ethanol outflow-to-inflow ratio does not represent skeletalmuscle BF but rather contraction-induced changes in molecular transport in the interstitium or over the microdialysis membrane.

     

Uptake and metabolism of biotin by human peripheral blood mononuclear cells

We studied the uptake of biotin into human peripheral bloodmononuclear cells (PBMC) using[³H]biotin and studiedthe catabolism of biotin in PBMC using[¹⁴C]biotin. Over 30 min, [³H]biotin uptakewas greater at 37°C than at 25°C(K_T = 2.6 ± 0.4 nM, maximal velocity = 2.9 ± 0.2 fmol · 10⁶cells¹ · 30 min¹). Ouabain reduced[³H]biotin uptake to65% of control values, suggesting that biotin uptake is Na-K-ATPasedependent. Unlabeled biotin and biotin analogs reduced the uptake of[³H]biotin to22-70% of control values, suggesting the presence of acompetition for a structurally specific biotin transporter. Whenendocytosis by PBMC was stimulated by various acyl glycerols, [³H]biotin uptake was40-73% of control values; these data are consistent with thehypothesis that stimulated endocytosis reduces biotin transporterdensity on the cell surface. During a 168-h incubation, PBMC did notcatabolize[¹⁴C]biotin.

     

Role of microtubules in the regulation of metabolism in isolated cerebral microvessels

We used¹³C-labeled substrates and nuclearmagnetic resonance spectroscopy to examine carbohydrate metabolism invascular smooth muscle of freshly isolated pig cerebral microvessels(PCMV). PCMV utilized[2-¹³C]glucose mainlyfor glycolysis, producing[2-¹³C]lactate.Simultaneously, PCMV utilized the glycolytic intermediate [1-¹³C]fructose1,6-bisphosphate (FBP) mainly for gluconeogenesis, producing[1-¹³C]glucose withonly minor[3-¹³C]lactateproduction. The dissimilarity in metabolism of[2-¹³C]FBP derivedfrom [2-¹³C]glucosebreakdown and metabolism of exogenous[1-¹³C]FBPdemonstrates that carbohydrate metabolism is compartmented in PCMV.Because glycolytic enzymes interact with microtubules, we disruptedmicrotubules with vinblastine. Vinblastine treatment significantlydecreased[2-¹³C]lactate peakintensity (87.8 ± 3.7% of control). The microtubule-stabilizing agent taxol also reduced[2-¹³C]lactate peakintensity (90.0 ± 2.4% of control). Treatment with both agentsfurther decreased[2-¹³C]lactateproduction (73.3 ± 4.0% of control). Neither vinblastine, taxol,or the combined drugs affected[1-¹³C]glucose peakintensity (gluconeogenesis) or disrupted the compartmentation ofcarbohydrate metabolism. The similar effects of taxol and vinblastine, drugs that have opposite effects on microtubule assembly, suggest thatthey produce their effects on glycolytic rate by competing withglycolytic enzymes for binding, not by affecting the overall assemblystate of the microtubule network. Glycolysis, but not gluconeogenesis,may be regulated in part by glycolytic enzyme-microtubule interactions.

     

Na+-K+-ATPase in frog esophagus mucociliary cell membranes: inhibition by protein kinase C activation

We examined protein kinase C (PKC)-dependentregulation ofNa⁺-K⁺-ATPasein frog mucociliary cells. Activation of PKC by12-O-tetradecanoylphorbol-13-acetate (TPA) or 1,2-dioctanoyl-sn-glycerol(diC8) either in intact cells or isolated membranes resulted in aspecific inhibition ofNa⁺-K⁺-ATPaseactivity by ~25-45%. The inhibitory effects in membranes exhibited time dependence and dose dependence [half-maximalinhibition concentration (IC₅₀) = 0.5 ± 0.1 nM and 2.4 ± 0.2 µM, respectively, for TPA anddiC8] and were not influenced byCa²⁺. Analysis of the ouabaininhibition pattern revealed the presence of twoNa⁺-K⁺-ATPaseisoforms with IC₅₀ values forcardiac glycoside of 2.6 ± 0.8 nM and 409 ± 65 nM,respectively. Most importantly, the isoform possessing a higheraffinity for ouabain was almost completely inhibited by TPA, whereasits counterpart was hardly sensitive to the PKC activator. The resultssuggest that, in frog mucociliary cells, PKC regulatesNa⁺-K⁺-ATPaseand that this action is related to the specificNa⁺-K⁺-ATPaseisoform.

     

K+ supplementation increases muscle [Na+-K+-ATPase] and improves extrarenal K+ homeostasis in rats

Bundgaard, Henning, Thomas A. Schmidt, Jim S. Larsen, andKeld Kjeldsen. K⁺supplementation increases muscle[Na⁺-K⁺-ATPase]and improves extrarenal K⁺homeostasis in rats. J. Appl. Physiol.82(4): 1136-1144, 1997.Effects ofK⁺ supplementation (~200 mmolKCl/100 g chow) on plasma K⁺,K⁺ content, andNa⁺-K⁺-adeonsinetriphosphatase(ATPase) concentration([Na⁺-K⁺-ATPase])in skeletal muscles as well as on extrarenalK⁺ clearance were evaluated inrats. After 2 days of K⁺supplementation, hyperkalemia prevailed(K⁺-supplemented vs.weight-matched control animals) [5.1 ± 0.2 (SE) vs. 3.2 ± 0.1 mmol/l, P < 0.05, n = 5-6], and after 4 daysa significant increase in K⁺content was observed in gastrocnemius muscle (104 ± 2 vs. 97 ± 1 µmol/g wet wt, P < 0.05, n = 5-6). After 7 days ofK⁺ supplementation, a significantincrease in[³H]ouabain bindingsite concentration (344 ± 5 vs. 239 ± 8 pmol/g wet wt,P < 0.05, n = 4) was observed in gastrocnemiusmuscle. After 2 wk, increases in plasmaK⁺,K⁺ content, and[³H]ouabain bindingsite concentration in gastrocnemius muscle amounted to 40, 8, and 68%(P < 0.05) above values observed inweight-matched control animals, respectively. The latter change wasconfirmed by K⁺-dependentp-nitrophenyl phosphatase activitymeasurements. Fasting for 1 day reduced plasmaK⁺ andK⁺ content in gastrocnemius musclein rats that had been K⁺supplemented for 2 wk by 3.1 ± 0.3 mmol/l(P < 0.05, n = 5) and 15 ± 2 µmol/g wet wt(P < 0.05, n = 5), respectively. After induction of anesthesia, arterial plasma K⁺was measured during intravenous KCl infusion (0.75 mmolKCl · 100 g bodywt¹ · h¹).The K⁺-supplemented fasted groupdemonstrated a 42% (P < 0.05) lower plasma K⁺ rise, associated with asignificantly higher increase inK⁺ content in gastrocnemius muscleof 7 µmol/g wet wt (P < 0.05, n = 5) compared with their controlanimals. In conclusion, K⁺supplementation increases plasmaK⁺,K⁺ content, and[Na⁺-K⁺-ATPase]in skeletal muscles and improves extrarenalK⁺ clearance capacity.

     

Postnatal expression and activity of the mitochondrial 2-oxoglutarate-malate carrier in intact hearts

This studyexamines the functional implications of postnatal changes in theexpression of the mitochondrial transporter protein, 2-oxoglutarate-malate carrier (OMC). Online ¹³C nuclearmagnetic resonance (¹³C NMR) measurements of isotopekinetics in hearts from neonate (3-4 days) and adult rabbitsprovided tricarboxylic acid cycle flux rates and flux rates throughOMC. Neonate and adult hearts oxidizing 2.5 mM[2,4-¹³C₂]butyrate were subjected toeither normal or high cytosolic redox state (2.5 mM lactate) conditionsto evaluate the recruitment of malate-aspartate activity and theresulting OMC flux. During development from neonate (3-4 days) toadult, mitochondrial protein density in the heart increased from19 ± 3% to 31 ± 2%, whereas OMC expression decreased by65% per mitochondrial protein content (P < 0.05).Correspondingly, OMC flux was lower in adults hearts than in neonatesby 73% (neonate = 7.4 ± 0.4, adult = 2.0 ± 0.1 µmol/min per 100 mg mitochondrial protein; P < 0.05). Despite clear changes in OMC content and flux, theresponsiveness of the malate-aspartate shuttle to increased cytosolicNADH was similar in both adults and neonates with an approximatethreefold increase in OMC flux (in densitometric units/100 mgmitochondrial protein: neonate = 25.8 ± 2.5, adult = 6.0 ± 0.2; P < 0.05). The¹³C NMR data demonstrate that OMC activity is a principalcomponent of the rate of labeling of glutamate.

     

Carbohydrate intake during prolonged cycling minimizes effect of glycemic index of preexercise meal

We studied the effects of the glycemicindex (GI) of preexercise meals on metabolism and performance whencarbohydrate (CHO) was ingested throughout exercise. Six well-trainedcyclists performed three counterbalanced trials of 2-h cycling at~70% of maximal oxygen uptake, followed by a performance ride of 300 kJ. Meals consumed 2 h before exercise consisted of 2 g CHO/kg bodymass of either high-GI potato (HGI trial) or low-GI pasta (LGI trial), or of a low-energy jelly (Con trial). Immediately before and throughout exercise, subjects ingested a 10 g/100 ml[U-¹⁴C]glucosesolution for a total of 24 ml/kg body mass. Despite differences inpreexercise glucose, insulin, and free fatty acids concentrations amongtrials, both total CHO oxidation for HGI, LGI, and Con trials,respectively, during steady-state exercise [403 ± 16, 376 ± 29, and 373 ± 24 (SE) g/2 h] andoxidation of the ingested CHO (65 ± 6, 57 ± 6, and 63 ± 5 g/2 h) were similar. There was no difference in time tocomplete the subsequent performance ride (946 ± 23, 954 ± 35, and 970 ± 26 s for HGI, LGI, and Con trials, respectively). WhenCHO is ingested during exercise in amounts presently recommended bysports nutrition guidelines, preexercise CHO intake has little effecton metabolism or on subsequent performance during prolonged cycling(~2.5 h).