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M D Stern

Publications and source records attributed to M D Stern.

At least 55 records · Page 3Linked to original sources
PubMed1996

Comparison of nitrogen-15 and purines as microbial markers in continuous culture.

Eight dual-flow continuous-culture fermenters were used in four replicated periods to compare the effects of diet and microbial marker on estimates of N metabolism in continuous culture of ruminal microorganisms. A basal diet was supplemented with urea and tryptone, soybean meal (SBM), lignosulfonate-treated SBM, corn gluten meal, blood meal (BM), hydrolyzed feather meal, fish meal (FM), or meat and bone meal (MBM). Microbial protein flow and protein degradation in fermenters were estimated using purines, purine N, and 15N in bacteria obtained from fermenter flasks or from the effluent. The ratio of purine N to total N in bacteria averaged .083 and was not affected (P > .05) by treatment. Dietary purine content (percentage of DM) ranged from .033 in BM to .084 in FM. Escape of feed purine N (percentage of total purine N flow) averaged 1.7% (SE = 2.9) and was not different (P > .05) among treatments. Bacterial N flows obtained using purines were more variable than estimates obtained using 15N. Bacterial N flows calculated using 15N in bacteria isolated from fermenters were more variable than those obtained using bacteria isolated from the effluent. The use of purines as a microbial marker resulted in lower estimates of protein degradation and smaller differences among treatments compared with use of 15N. Data suggest that escape of feed purine N seems to be a minor factor affecting calculation of bacterial N flow and that the use of 15N in effluent bacteria may be a more accurate procedure when using continuous-culture fermenters.

Animals↗
PubMed1996

Effects of Saccharomyces cerevisiae and Aspergillus oryzae cultures on ruminal fermentation in dairy cows.

Four lactating Holstein cows, fitted with ruminal and duodenal cannulas, were used in a 4 x 4 Latin square design to examine the effects of supplemental yeast (Saccharomyces cerevisiae) and fungal (Aspergillus oryzae) cultures on ruminal fermentation, microbial populations, and nutrient supply to the small intestine. Cows were fed a basal diet comprising 32.5% corn silage, 17.5% alfalfa hay, 35.3% corn grain, 12.7% soybean meal, and 2% vitamin and mineral mixture on a DM basis. Treatments were arranged in a 2 x 2 factorial as follows: 1) basal diet, 2) basal diet plus 57 g/d of yeast culture, 3) basal diet plus 3 g/d of fungal culture, and 4) basal diet plus 57 g/d of yeast culture and 3 g/d of fungal culture. Ruminal pH, ammonia N concentration, and total VFA concentration were similar among treatments. Molar percentages of ruminal isoacids were lower for cows fed a mixture of yeast and fungal culture than for cows fed yeast or fungal culture alone. Yeast culture increased ruminal OM and CP digestion and decreased OM and N flow to the duodenum. Fiber digestion in the rumen was similar among treatments. Fungal culture stimulated proteolytic and cellulolytic bacterial counts. Proteolytic bacterial counts were also stimulated by yeast culture. Results from this experiment demonstrated that yeast and fungal cultures could influence ruminal fermentation and microbial populations.

Ammonia↗
PubMed1995

Mitochondrial membrane potential in single living adult rat cardiac myocytes exposed to anoxia or metabolic inhibition.

1. The relation between mitochondrial membrane potential (delta psi m) and cell function was investigated in single adult rat cardiac myocytes during anoxia and reoxygenation. delta psi m was studied by loading myocytes with JC-1 (5,5',6,6'-tetrachloro-1,1',3,3'- tetra-ethylbenzimidazolylcarbocyanine iodide), a fluorescent probe characterized by two emission peaks (539 and 597 nm with excitation at 490 nm) corresponding to monomer and aggregate forms of the dye. 2. De-energizing conditions applied to mitochondria, cell suspensions or single cells decreased the aggregate emission and increased the monomer emission. This latter result cannot be explained by changes of JC-1 concentration in the aqueous mitochondrial matrix phase indicating that hydrophobic interaction of the probe with membranes has to be taken into account to explain JC-1 fluorescence properties in isolated mitochondria or intact cells. 3. A different sensitivity of the two JC-1 forms to delta psi m changes was shown in isolated mitochondria by the effects of ADP and FCCP and the calibration with K+ diffusion potentials. The monomer emission was responsive to values of delta psi m below 140 mV, which hardly modified the aggregate emission. Thus JC-1 represents a unique double sensor which can provide semi-quantitative information in both low and high potential ranges. 4. At the onset of glucose-free anoxia the epifluorescence of individual myocytes studied in the single excitation (490 nm)-double emission (530 and 590 nm) mode showed a gradual decline of the aggregate emission, which reached a plateau while electrically stimulated (0.2 Hz) contraction was still retained. The subsequent failure of contraction was followed by the rise of the emission at 530 nm, corresponding to the monomer form of the dye, concomitantly with the development of rigor contracture. 5. The onset of the rigor was preceded by the increase in intracellular Mg2+ concentration ([Mg2+]i) monitored by mag-indo-1 epifluorescence. Since under these experimental conditions intracellular [Ca2+] and pH are fairly stable, the increase in [Mg2+]i was likely to be produced by a decrease in ATP content. 6. The inhibition of mitochondrial ATPase induced by oligomycin during anoxia was associated with a rapid and simultaneous change of both the components of JC-1 fluorescence, suggesting that delta psi m, instead of producing ATP, is generated by glycolytic ATP during anoxia. 7. The readmission of oxygen induced a rapid decrease of the monomer emission and a slower increase of the aggregate emission. These fluorescence changes were not necessarily associated with the recovery of mechanical function.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Diphosphate↗
PubMed1995

Consequences of altered aspartate aminotransferase activity on 13C-glutamate labelling by the tricarboxylic acid cycle in intact rat hearts.

The appearance of 13C label in glutamate has been used to quantify cellular tricarboxylic acid (TCA) cycle activity using 13C-NMR spectroscopy. Glutamate is linked to the TCA cycle by the amino-transferase reactions, however the consequences of alterations in amino-transferase activity on glutamate labelling kinetics, at a constant total tricarboxylic acid cycle activity, have not been investigated. Aspartate amino-transferase activity in [2-13C]acetate-perfused beating rat hearts was found to be similar to total TCA cycle flux in the presence of normal perfusion conditions and was reduced by more than 50% with the subsequent administration of amino-oxyacetic acid (AOA). AOA did not reduce contractile or kinetic measures of total TCA cycle flux, but did slow the 13C labelling of glutamate, in accord with current mathematical predictions. The impact of similar reductions in amino-transferase activity on estimates of total TCA cycle flux derived from several previously reported methods was also evaluated. Because total TCA cycle and the amino-transferase activities both affect the kinetics of 13C-glutamate labelling and because the amino-transferase activities are often unknown under physiologic conditions and can be reduced under pathologic conditions, the calculation of total TCA cycle flux from 13C-NMR data in the future is probably best accomplished either with a sufficiently sophisticated mathematical model that assesses amino-transferase activity or with an empiric model that is relatively insensitive to variations in amino-transferase activity.

Aminooxyacetic Acid↗
PubMed1995

Effects of sarcoplasmic reticulum Ca2+ load on the gain function of Ca2+ release by Ca2+ current in cardiac cells.

We studied the effects of variable sarcoplasmic reticulum (SR) Ca2+ loading on changes in the gain index of Ca2+ release from the SR, measured as the ratio of the amount of Ca2+ released to the magnitude of the Ca2+ current (ICa) integrated for the initial 20 ms of the depolarization, in whole cell voltage-clamped rat ventricular myocytes dialyzed with the Ca2+ indicator indo 1 salt at 23 degrees C. Changes in ICa were measured directly, and changes in the SR Ca2+ release were indexed by changes in the amplitudes and rates of rise of cytosolic Ca2+ (Ca2+i) transients. The SR Ca2+ load was graded by the duration of conditioning voltage-clamp steps and verified by caffeine-dependent Ca2+i transients. A train of abbreviated (from 100 to 20 ms) voltage-clamp depolarizations, which triggers SR Ca2+ release but fails to replenish the SR with Ca2+, diminished the SR Ca2+ load by 56 +/- 5%, did not alter peak ICa but reduced the amplitudes of the ICa-dependent Ca2+i transients by 52 +/- 3%, and decreased the gain index by 60 +/- 3% (SE; n = 5 or 6). Changes in the amplitudes of Ca2+i transients elicited by ICa and changes in the gain index were linearly correlated (r2 = 0.83 and 0.79, respectively; P < 0.001 for each) with changes in amplitudes of Ca2+i transients elicited by caffeine pulses applied in lieu of the respective voltage-clamp pulses.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

A three-step in vitro procedure for estimating intestinal digestion of protein in ruminants.

A three-step in vitro procedure was developed to estimate intestinal digestion of proteins in ruminants. Dacron bags containing feed samples were suspended in the rumen for 16 h. Residue containing 15 mg of N after ruminal exposure was incubated for 1 h in 10 mL of a .1 N HCl solution containing 1 g/L of pepsin. After incubation, pH was neutralized with .5 mL of 1 N NaOH and 13.5 mL of a pH 7.8 phosphate buffer containing 37.5 mg of pancreatin were added to the solution and incubated at 38 degrees C. After a 24-h incubation, 3 mL of a 100% (wt/vol) trichloroacetic acid solution were added to precipitate undigested proteins. Preincubation of samples in the rumen did not affect (P > .05) pepsin-pancreatin digestion of residual CP in soybean meal (SBM), corn gluten meal (CGM), and blood meal (BM) and reduced (P < .05) pepsin-pancreatin digestion of residual CP in hydrolyzed feather meal (HFM), fish meal (FM), and meat and bone meal (MBM) (80 vs 70, 88 vs 81, and 82 vs 56%, respectively, for nonruminal vs ruminal preincubation). Pepsin digestion before pancreatin digestion increased (P < .05) CP digestion of all proteins tested by a mean of 23 percentage units. The pancreatin digestion step was validated using 34 duodenal samples from which small intestinal CP digestion was determined in vivo. The regression equation of in vivo estimates on pancreatin digestion had an r value of .91 (P < .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Effects of protein source on nitrogen metabolism in continuous culture and intestinal digestion in vitro.

Eight dual flow continuous culture fermenters were used in four replicated periods to study the effects of protein supplements on ruminal fermentation and CP digestion. A basal diet was supplemented with isonitrogenous amounts of urea and tryptone (control; CTRL), soybean meal (SBM), lignosulfonate-treated SBM (LSBM), corn gluten meal (CGM), blood meal (BM), hydrolyzed feather meal (HFM), fish meal (FM), or meat and bone meal (MBM). Digestion of DM, OM, and carbohydrates was not affected by treatment. Ammonia N concentration was highest (P < .05) for CTRL and lowest (P < .05) for LSBM, CGM, BM, HFM, and FM. Nonammonia N flow was lowest (P < .05) for CTRL. Dietary N flow was lowest (P < .05) for CTRL, intermediate for SBM, and highest (P < .05) for LSBM, CGM, BM, HFM, FM, and MBM. Total N flow, bacterial N flow, and efficiency of microbial protein synthesis were not affected by treatment. Protein degradation was highest (P < .05) for CTRL. Flow of total amino acids (AA) was lowest (P < .05) for CTRL, SBM, and MBM. Diets containing BM provided the largest (P < .05) amounts of essential AA and lysine, and FM provided the largest (P < .05) amounts of methionine in fermenter effluent. Supplementation of diets with proteins low in ruminal degradability increased flows of nonammonia N, dietary N, and total and essential AA and modified the AA profile flowing out of fermenters.

Amino Acids↗
PubMed1995

Effects of ruminal versus duodenal dosing of fish meal on ruminal fermentation and milk composition.

Three midlactation Holstein cows with ruminal and duodenal cannulas were used in a 3 x 3 Latin square design to determine whether ruminal or postruminal alterations in metabolism were responsible for the changes in milk composition that frequently are associated with dietary fish meal. Cows were offered a diet of 60:40 forage to concentrate (aliquots at 6-h intervals) that was supplemented with isonitrogenous amounts of soybean meal (1.3 kg of DM/d) dosed into the rumen or fish meal (1.0 kg DM/d) dosed either into the rumen or into the duodenum. The DMI, ruminal NDF digestion, and flows of total N and microbial N to the duodenum decreased for cows receiving fish meal. Dietary N flow increased when fish meal was dosed into the rumen. Total concentration of ruminal VFA was greater for cows receiving the soybean meal treatment; however, treatment had no effect on the ratio of ruminal acetate plus butyrate to propionate. Milk and FCM yields were unaffected by treatment, but milk fat content decreased, and milk protein content increased when cows were supplemented with fish meal. The difference in mammary arteriovenous glucose difference decreased when cows were dosed with fish meal. Changes in plasma NEFA and triglycerides were small and inconsistent. Results from this experiment suggest that effects of fish meal on milk composition are due to postruminal alterations in metabolism.

Acetates↗
PubMed1994

Regulation of intracellular free Mg2+ and contraction in single adult mammalian cardiac myocytes.

Studies in isolated cardiac myocytes have increased our understanding of intracellular Ca2+ regulation. Because less is known about Mg2+ regulation, adult rat ventricular myocytes were loaded with the Mg(2+)-sensitive fluorescent probe mag-indo 1, and changes in intracellular Mg2+ concentration ([Mg2+]i) and cell length were examined under a variety of conditions. The fluorescent signal was calibrated intracellularly and found to differ slightly from that for the probe in solution. Roughly 40% of the signal was intramitochondrial; the remainder was localized in the cytosol. Basal [Mg2+]i averaged 1.02 +/- 0.03 mM (n = 53 cells). No change in [Mg2+]i was observed during a single electrically stimulated contraction, and only a minor increase was seen during rapid electrical stimulation, which was expected to raise intracellular Ca2+ concentration ([Ca2+]i) to approximately 1 microM. An acid shift in intracellular pH of approximately 1 pH unit was accompanied by a small change in [Mg2+]i (0.34 +/- 0.03 mM, n = 6, P < 0.05). No change in [Mg2+]i was observed when cells were superfused with 15 mM Mg2+, despite marked changes in contraction. [Mg2+]i more than doubled when cells were depleted of ATP by exposure to hypoxia or metabolic inhibitors. The increase in [Mg2+]i was abrupt and occurred at the time of the failure of contraction, plateauing as rigor contracture developed. Reoxygenation was accompanied by a gradual fall in [Mg2+]i in cells that recovered mechanical function, and in a subset of cells that underwent hypercontracture. Studies in cell suspensions confirmed that rapid cellular energy depletion was accompanied by increases in [Mg2+]i and parallel decreases in ATP. Thus [Mg2+]i was largely insensitive to changes in [Ca2+]i or pHi and extracellular [Mg2+] but was rapidly altered by changes in energy state in a manner that was related to specific changes in cell morphology and contractile function.

Adenosine Triphosphate↗
PubMed1994

Sodium channel blockade reduces hypoxic sodium loading and sodium-dependent calcium loading.

BACKGROUND: Studies have shown that the rise in intracellular ionized calcium, [Ca2+]i, in hypoxic myocardium is driven by an increase in sodium, [Na+]i, but the source of Na+ is not known. METHODS AND RESULTS: Inhibitors of the voltage-gated Na+ channel were used to investigate the effect of Na+ channel blockade on hypoxic Na+ loading, Na(+)-dependent Ca2+ loading, and reoxygenation hypercontracture in isolated adult rat cardiac myocytes. Single electrically stimulated (0.2 Hz) cells were loaded with either SBFI (to index [Na+]i) or indo-1 (to index [Ca2+]i) and exposed to glucose-free hypoxia (PO2 < 0.02 mm Hg). Both [Na+]i and [Ca2+]i increased during hypoxia when cells became inexcitable following ATP-depletion contracture. The hypoxic rise in [Na+]i and [Ca2+]i was significantly attenuated by 1 mumol/L R 56865. Tetrodotoxin (60 mumol/L), a selective Na(+)-channel blocker, also markedly reduced the rise in [Ca2+]i during hypoxia and reoxygenation. Reoxygenation-induced cellular hypercontracture was reduced from 83% (45 of 54 cells) under control conditions to 12% (4 of 32) in the presence of R 56865 (P < .05). Lidocaine reduced hypercontracture dose dependently with 13% of cells hypercontracting in 100 mumol/L lidocaine, 42% in 50 mumol/L lidocaine, and 93% in 25 mumol/L lidocaine. The Na(+)-H+ exchange blocker, ethylisopropylamiloride (10 mumol/L) was also effective, limiting hypercontracture to 12%. R 56865, lidocaine, and ethylisopropylamiloride were also effective in preventing hypercontracture in normoxic myocytes induced by 75 mumol/L veratridine, an agent that impairs Na+ channel inactivation. Ethylisopropylamiloride prevented the veratridine-induced rise in [Ca2+]i without affecting Na(+)-Ca2+ exchange, suggesting that amiloride derivatives can reduce Ca2+ loading by blocking Na+ entry through Na+ channels, an action that may in part underlie their ability to prevent hypoxic Na+ and Ca2+ loading. CONCLUSIONS: Na+ influx through the voltage-gated Na+ channel is an important route of hypoxic Na+ loading, Na(+)-dependent Ca2+ loading, and reoxygenation hypercontracture in isolated rat cardiac myocytes. Importantly, the Na+ channel appears to serve as a route for hypoxic Na+ influx after myocytes become inexcitable.

Amiloride↗
PubMed1994

Influence of non-fibrous carbohydrate and degradable intake protein on fermentation by ruminal microorganisms in continuous culture.

Four continuous culture fermenters were used in a 4 x 4 Latin square design to evaluate the effects of dietary non-fibrous carbohydrate (NFC) and ruminally degradable intake protein (DIP) on fermentation by ruminal microorganisms. Four diets, arranged in a 2 x 2 factorial, were formulated to contain either 25 or 40% NFC and 50 or 70% of dietary CP as DIP. Dietary DM contained 32% corn silage, 20% alfalfa-grass hay, and 48% concentrate. Solvent-extracted or lignosulfonate-treated soybean meal were used to alter DIP and contributed 40% of dietary CP. Corn or soybean hulls were included at 28% of dietary DM to alter NFC levels. Percentage of true OM digestion was similar (P > .05) among diets but NDF and total nonstructural carbohydrate digestion were inversely related depending on NFC content of the diet. Amylolytic bacterial concentrations (cells/milliliter) were lower (P = .03) in fermenters supplied with 25% NFC diets, resulting in less (P = .0001) total nonstructural carbohydrate digestion. Cellulolytic concentrations were similar (P > .05) among diets despite an increase (P = .002) in NDF digestion with 25% NFC diets. Total viable bacterial concentrations tended to decrease (P = .11) with 50% DIP diets, inducing a decline (P = .03) in total VFA production (millimoles/day). Reduced degradation of CP in 50% DIP diets (P = .008) increased outflow of total amino acid (P = .07) and individual outflows (P < .05) of glutamic acid, aspartic acid, arginine, histidine, and lysine. Few interactions occurred for the parameters measured despite the controlled nature of the fermentation in the current experiment. The preponderance of significant main effects illustrates that ruminal fermentation may not be improved by synchronization of energy and N release but may more likely be limited by either energy or N alone.

Amino Acids↗
PubMed1994

Effects of beet pulp and animal by-products on milk yield and in vitro fermentation by rumen microorganisms.

Forty-six Holstein cows (30 primiparous) were assigned to one of four dietary treatments arranged as a 2 x 2 factorial experiment during wk 4 to 17 of lactation. Main effects were corn versus dried sugar beet pulp and soybean meal versus animal by-product meal (mixture of meat and bone meal, feather meal, and blood meal). Beet pulp replaced half of the corn at 15% of dietary DM. Diet DM (mean of four treatments) contained 18% alfalfa pellets, 17.4% alfalfa hay, 17.2% corn silage, and 47.1% concentrate. Milk yield did not differ among treatments (mean 32.0 kg/d). Dry matter intake, milk CP percentage, and milk CP yield decreased 5.6, 3.7 and 5.2%, respectively, but milk fat percentage increased 4.7% when beet pulp replaced corn. Animal by-products did not affect DMI or milk fat, but milk CP percentage decreased 3.0%. The same diets were evaluated in a continuous culture system. Fungal extract (Aspergillus oryzae), added as the third treatment, had little effect on fermentation. Digestion of DM, OM, NDF, and ADF were not affected by dietary treatments. Molar proportion of acetate was greater when corn was replaced by beet pulp. Although flow of NAN from fermenters increased by 3.2% with beet pulp and 3.1% with animal by-products, milk CP percentages decreased.

Animal Feed↗
PubMed1994

Effects of soybean hulls and lignosulfonate-treated soybean meal on ruminal fermentation in lactating dairy cows.

Four Holstein cows were used in a 4 x 4 Latin square design to investigate the effects of soybean hulls and lignosulfonate-treated soybean meal on ruminal fermentation and nutrient passage to the duodenum. Diets contained 32% corn silage, 19.8% alfalfa-grass hay, and 48.2% concentrate (DM basis). Treatments, arranged in a 2 x 2 factorial, were concentrate mixes based on 1) corn and soybean meal, 2) corn and treated soybean meal, 3) soybean hulls and soybean meal, and 4) soybean hulls and treated soybean meal. Individual protein supplements supplied 40% of dietary CP, and corn or soybean hulls constituted 28% of dietary DM. Intake of OM (mean 18.9 kg/d) was similar among treatments, but intake of NDF was 42% greater, and intake of nonstructural carbohydrate was 55% less, for cows fed soybean hulls. Passage of OM to the duodenum was similar among diets, but flow of NDF was 43% greater, and flow of nonstructural carbohydrate was 56% less, for cows fed soybean hulls. Ruminal pH was similar, but total concentrations of VFA increased 7% when soybean hulls replaced corn. Ruminal digestion of dietary CP was 15% less for cows fed treated soybean meal, but bacterial N flows were similar among treatments. Soybean hulls were digested to a similar extent as corn, but few interactions occurred between supplemental carbohydrate and protein sources.

Amino Acids↗
PubMed1994

Effects of extruded soybeans and forage source on fermentation by rumen microorganisms in continuous culture.

Continuous culture fermenters were used to evaluate effects of extrusion of whole soybeans and changes in forage composition of diets on microbial fermentation. Treatments were arranged in a 2 x 4 factorial design with soybeans (raw or extruded) and dietary treatment (ratio of alfalfa hay to corn silage; 82:18, 61:39, 43:57, and 27:73 of dietary forage) as main effects. Soybeans constituted 9.6, 14.4, 19.2, and 23.9% of DM for each of the respective dietary treatments. True digestion of DM, ADF, and NDF was unaffected by processing of soybeans or dietary treatment, but true digestion of OM decreased as concentration of corn silage and soybeans increased. Total VFA concentration was unaffected by source of soybeans or dietary treatments; however, molar concentration of butyrate decreased in fermenters supplied with diets containing extruded soybeans. Degradation of CP was not influenced by soybean source but decreased as the concentration of corn silage and soybeans increased. Bacterial N output decreased, and dietary N flow from the fermenters increased, as concentration of corn silage and soybeans increased. Changes in the ratio of alfalfa hay to corn silage and alteration of dietary soybean concentration affected true OM digestion and dietary CP degradation, but extrusion of whole soybeans had little effect on fermentation.

Animal Feed↗
PubMed1994

Evaluation of chemical and physical properties of feeds that affect protein metabolism in the rumen.

The goal of the NC-185 Cooperative Regional Research Project is to provide the information needed to improve the nutrition and feeding of dairy cattle, a major factor determining composition of milk and cost of milk yield. Emphasis is placed on understanding how energy and protein nutrition of lactating cows can be manipulated to increase the quantity and improve the profile of AA passing to the small intestine and to improve yield of milk and milk protein. To achieve this goal, one of the major objectives of this project has been to evaluate quantitatively the chemical and physical properties of protein and energy sources that determine AA availability to lactating cows. Reliable measurements of microbial protein synthesis and protein degradation in the rumen are critical in the evaluation process. Therefore, one of the ongoing areas of investigation of this research project has been to determine the most appropriate methods for estimating microbial protein synthesis and dietary protein degradation in the rumen. Other areas have been investigated, using continuous culture fermenters and ruminally and duodenally cannulated cows, including factors that alter microbial metabolism of N in the rumen and subsequently protein supply to the small intestine, such as sources of carbohydrate, protein, and fat and interrelationships of protein and carbohydrate. Findings of the NC-185 Cooperative Regional Research Project Committee and other investigators are summarized in this review.

Animal Feed↗
PubMed1993

Tricarboxylic acid cycle activity in postischemic rat hearts.

BACKGROUND: Although myocardial oxidative tricarboxylic acid (TCA) cycle activity and contractile function are closely linked in normal cardiac muscle, their relation during postischemic reperfusion, when contractility often is reduced, is not well defined. METHODS AND RESULTS: To test the hypothesis that oxidative TCA cycle flux is reduced in reperfused myocardium with persistent contractile dysfunction, TCA cycle flux was measured by analyzing the time course of sequential myocardial glutamate labeling during 13C-labeled substrate infusion with 13C nuclear magnetic resonance spectroscopy in beating isolated rat hearts at 37 degrees C. Total TCA cycle flux, indexed by both empirical and mathematical modeling analyses of the 13C data, was not reduced but rather increased in hearts reperfused after 17-20 minutes of ischemia (left ventricular pressure, 73 +/- 5% of preischemic values) compared with flux in developed pressure-matched controls (e.g., total flux, 2.5 +/- 0.4 versus 1.6 +/- 0.1 mumol.min-1.g wet wt-1, respectively; p < 0.01). No TCA cycle activity was detectable by 13C nuclear magnetic resonance in hearts reperfused after 40-45 minutes of ischemia, which lacked contractile recovery and had ultrastructural evidence of irreversible injury. CONCLUSIONS: These results suggest that TCA cycle activity is not persistently decreased in dysfunctional reperfused myocardium after a brief ischemic episode and therefore cannot account for the reduced contractile function at that time.

Animals↗
PubMed1992

Spontaneous sarcoplasmic reticulum Ca2+ release leads to heterogeneity of contractile and electrical properties of the heart.

The cytosolic Ca2+ (Cai) oscillation generated by the sarcoplasmic reticulum (SR) in response to an action potential (AP) occurs relatively synchronously within and among cells. The SR can also generate spontaneous Cai oscillations (S-CaOs), i.e., not triggered by sarcolemmal depolarization. The local increase in Cai due to S-CaOs is equivalent to that induced by an AP. Heterogeneity of diastolic Cai caused by asynchronous S-CaOs among cells within myocardial tissue leads to heterogeneous myofilament activation, the summation of which produces a Ca(2+)-dependent component to diastolic tone. The local increases in Cai due to S-CaOs also cause oscillatory sarcolemmal depolarizations due to Ca2+ modulation of the Na/Ca exchanger and of non-specific cation channels. Thus, inhomogeneous levels of diastolic Cai may lead to heterogeneity in cell coupling and thus may also affect the impulse conduction. The magnitude of the S-CaOs induced diastolic tonus and membrane depolarization varies with the extent to which S-CaOs are synchronized; partially synchronized S-CaOs following an AP induced SR Ca2+ release produce an aftercontraction and after depolarization. When local S-CaOs is sufficiently synchronized within the cell the resultant depolarization summates and can be sufficient to trigger spontaneous AP. Inhomogeneity of diastolic SR Ca2+ loading and sarcomere lengths within individual cardiac cells due to S-CaOs leads to inhomogeneous systolic Cai levels and sarcomere length inhomogeneities in response a subsequent AP; this heterogeneity compromises the systolic contraction amplitude. Heterogeneity of systolic Cai among cells due to diastolic S-CaOs also leads to heterogeneity of AP repolarization times, due, to heterogeneous Cai modulation of the Na/Ca exchanger, the non-specific cation channel and of the L type sarcolemmal Ca2+ channel. S-CaOs occurrence during a long AP plateau may also modulate the removal of voltage inactivation of L type Ca2+ channels and affect the likelihood of the occurrence of "early after depolarizations." Thus, as a single entity, S-CaOs may be implicated in diverse manifestations of heart failure--impaired systolic performance, increased diastolic tonus and an increased probability for the occurrence of arrhythmias.

Animals↗