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M D Stern

Publications and source records attributed to M D Stern.

At least 19 recordsLinked to original sources
PubMed2005

Nitrogen metabolism in the rumen.

Protein metabolism in the rumen is the result of metabolic activity of ruminal microorganisms. The structure of the protein is a key factor in determining its susceptibility to microbial proteases and, thus, its degradability. Ruminal protein degradation is affected by pH and the predominant species of microbial population. Ruminal proteolytic activity decreases as pH decreases with high-forage dairy cattle-type rations, but not in high-concentrate beef-type rations. Accumulation of amino acid (AA) N after feeding suggests that AA uptake by rumen microorganisms could be the limiting factor of protein degradation in the rumen. In addition, there are several AA, such as Phe, Leu, and Ile, that are synthesized by rumen microorganisms with greater difficulty than other AA. The most common assessment of efficiency of microbial protein synthesis (EMPS) is determination of grams of microbial N per unit of rumen available energy, typically expressed as true organic matter or carbohydrates fermented. However, EMPS is unable to estimate the efficiency at which bacteria capture available N in the rumen. An alternative and complementary measure of microbial protein synthesis is the efficiency of N use (ENU). In contrast to EMPS, ENU is a good measurement for describing efficiency of N capture by ruminal microbes. Using EMPS and ENU, it was concluded that optimum bacterial growth in the rumen occurs when EMPS is 29 g of bacterial N/kg of fermented organic matter, and ENU is 69%, implying that bacteria would require about 1.31 x rumen-available N per unit of bacterial N. Because the distribution of N within bacterial cells changes with rate of fermentation, AA N, rather than total bacterial N should be used to express microbial protein synthesis.

Amino Acids↗
PubMed2004

The elementary events of Ca2+ release elicited by membrane depolarization in mammalian muscle.

Cytosolic [Ca(2+)] transients elicited by voltage clamp depolarization were examined by confocal line scanning of rat skeletal muscle fibres. Ca(2+) sparks were observed in the fibres' membrane-permeabilized ends, but not in responses to voltage in the membrane-intact area. Elementary events of the depolarization-evoked response could be separated either at low voltages (near -50 mV) or at -20 mV in partially inactivated cells. These were of lower amplitude, narrower and of much longer duration than sparks, similar to 'lone embers' observed in the permeabilized segments. Their average amplitude was 0.19 and spatial half-width 1.3 microm. Other parameters depended on voltage. At -50 mV average duration was 111 ms and latency 185 ms. At -20 mV duration was 203 ms and latency 24 ms. Ca(2+) release current, calculated on an average of events, was nearly steady at 0.5-0.6 pA. Accordingly, simulations of the fluorescence event elicited by a subresolution source of 0.5 pA open for 100 ms had morphology similar to the experimental average. Because 0.5 pA is approximately the current measured for single RyR channels in physiological conditions, the elementary fluorescence events in rat muscle probably reflect opening of a single RyR channel. A reconstruction of cell-averaged release flux at -20 mV based on the observed distribution of latencies and calculated elementary release had qualitatively correct but slower kinetics than the release flux in prior whole-cell measurements. The qualitative agreement indicates that global Ca(2+) release flux results from summation of these discrete events. The quantitative discrepancies suggest that the partial inactivation strategy may lead to events of greater duration than those occurring physiologically in fully polarized cells.

Animals↗
PubMed2003

Ca2+ sparks and embers of mammalian muscle. Properties of the sources.

Ca2+ sparks of membrane-permeabilized rat muscle cells were analyzed to derive properties of their sources. Most events identified in longitudinal confocal line scans looked like sparks, but 23% (1,000 out of 4,300) were followed by long-lasting embers. Some were preceded by embers, and 48 were "lone embers." Average spatial width was approximately 2 microm in the rat and 1.5 microm in frog events in analogous solutions. Amplitudes were 33% smaller and rise times 50% greater in the rat. Differences were highly significant. The greater spatial width was not a consequence of greater open time of the rat source, and was greatest at the shortest rise times, suggesting a wider Ca2+ source. In the rat, but not the frog, spark width was greater in scans transversal to the fiber axis. These features suggested that rat spark sources were elongated transversally. Ca2+ release was calculated in averages of sparks with long embers. Release current during the averaged ember started at 3 or 7 pA (depending on assumptions), whereas in lone embers it was 0.7 or 1.3 pA, which suggests that embers that trail sparks start with five open channels. Analysis of a spark with leading ember yielded a current ratio ranging from 37 to 160 in spark and ember, as if 37-160 channels opened in the spark. In simulations, 25-60 pA of Ca2+ current exiting a point source was required to reproduce frog sparks. 130 pA, exiting a cylindric source of 3 microm, qualitatively reproduced rat sparks. In conclusion, sparks of rat muscle require a greater current than frog sparks, exiting a source elongated transversally to the fiber axis, constituted by 35-260 channels. Not infrequently, a few of those remain open and produce the trailing ember.

Animals↗
PubMed2002

Persistence and functional impact of a microbial inoculant on native microbial community structure, nutrient digestion and fermentation characteristics in a rumen model.

Small sub-unit (SSU) rRNA-targeted oligonucleotide probes were used to monitor the persistence of a genetically engineered bacterium inoculated in model rumens. Eight dual flow continuous culture fermenters were operated with either standard artificial saliva buffer or buffer with chondroitin sulfate (0.5 g/l) added. After 168 h of operation, fermenters were inoculated with Bacteroides thetaiotaomicron BTX (BTX), at approximately 1% of total bacteria. B. thetaiotaomicron was quantified using a species-specific probe and shown to persist in fermenters 144 h after inoculation (relative abundance 0.48% and 1.42% of total SSU rRNA with standard and chondroitin sulfate buffers, respectively). No B. thetaiotaomicron SSU rRNA was detected in fermenter samples prior to inoculation with strain BTX. Relative abundances of Bacteria, Eucarya and Archaea were not affected by either inoculation or buffer type. Fiber digestion, in particular the hemicellulose fraction, increased after strain BTX addition. Chondroitin sulfate addition to the buffer increased bacterial nitrogen flow in fermenters, but did not alter fiber digestion. Neither inoculum nor buffer type altered total short chain fatty acid (VFA) concentrations but proportions of individual VFA differed. In model rumens, B. thetaiotaomicron BTX increased fiber digestion when added to mixed ruminal microbes, independent of chondroitin sulfate addition; but further study is needed to determine effects on other fiber-digesting bacteria.

Animals↗
PubMed2001

A preferred amplitude of calcium sparks in skeletal muscle.

In skeletal and cardiac muscle, calcium release from the sarcoplasmic reticulum, leading to contraction, often results in calcium sparks. Because sparks are recorded by confocal microscopy in line-scanning mode, their measured amplitude depends on their true amplitude and the position of the spark relative to the scanned line. We present a method to derive from measured amplitude histograms the actual distribution of spark amplitudes. The method worked well when tested on simulated distributions of experimental sparks. Applied to massive numbers of sparks imaged in frog skeletal muscle under voltage clamp in reference conditions, the method yielded either a decaying amplitude distribution (6 cells) or one with a central mode (5 cells). Caffeine at 0.5 or 1 mM reversibly enhanced this mode (5 cells) or induced its appearance (4 cells). The occurrence of a mode in the amplitude distribution was highly correlated with the presence of a mode in the distribution of spark rise times or in the joint distribution of rise times and spatial widths. If sparks were produced by individual Markovian release channels evolving reversibly, they should not have a preferred rise time or amplitude. Channel groups, instead, could cooperate allosterically or through their calcium sensitivity, and give rise to a stereotyped amplitude in their collective spark.

Algorithms↗
PubMed2001

Ion concentration-dependence of rat cardiac unitary L-type calcium channel conductance.

Little is known about the native properties of unitary cardiac L-type calcium currents (i(Ca)) measured with physiological calcium (Ca) ion concentration, and their role in excitation-contraction (E-C) coupling. Our goal was to chart the concentration-dependence of unitary conductance (gamma) to physiological Ca concentration and compare it to barium ion (Ba) conductance in the absence of agonists. In isolated, K-depolarized rat myocytes, i(Ca) amplitudes were measured using cell-attached patches with 2 to 70 mM Ca or 2 to 105 mM Ba in the pipette. At 0 mV, 2 mM of Ca produced 0.12 pA, and 2 mM of Ba produced 0.19 pA unitary currents. Unitary conductance was described by a Langmuir isotherm relationship with a maximum gammaCa of 5.3 +/- 0.2 pS (n = 15), and gammaBa of 15 +/- 1 pS (n = 27). The concentration producing half-maximal gamma, Kd(gamma), was not different between Ca (1.7 +/- 0.3 mM) and Ba (1.9 +/- 0.4 mM). We found that quasi-physiological concentrations of Ca produced currents that were as easily resolvable as those obtained with the traditionally used higher concentrations. This study leads to future work on the molecular basis of E-C coupling with a physiological concentration of Ca ions permeating the Ca channel.

Animals↗
PubMed2001

Effects of carbohydrates from citrus pulp and hominy feed on microbial fermentation in continuous culture.

Eight dual-flow continuous-culture fermenters were used to evaluate the effect of neutral detergent-soluble carbohydrates (NDSC) on fermentation by ruminal microorganisms. Citrus pulp and hominy feed were added to a basal diet as sources of NDSC, with citrus pulp providing neutral detergent-soluble fiber (NDSF) in the form of pectic substances and with hominy feed in the form of starch. The basal diet contained 26.7% corn silage, 6.0% alfalfa hay and 3.8% cottonseed hulls on a DM basis. The dried citrus pulp diet contained on a DM basis 17.2% CP, 34.7% NDF, 33.7% NDSC, and 14.4% NDSF, whereas the hominy feed diet contained 17.9% CP, 33.2% NDF, 35.9% NDSC, and 8.8% NDSF. Organic matter, DM, and NDF and ADF digestion were not affected by source of carbohydrate. Ammonia N concentration was greater (P < 0.05) for the hominy feed diet (14.2 mg/100 mL) than for the dried citrus pulp diet (9.3 mg/100 mL). Total N, nonammonia N, microbial N, and dietary N flows were not affected by treatments; however, the efficiency of microbial protein synthesis was greater (P = 0.055) for the dried citrus pulp diet than for the hominy feed diet (30.6 vs 27.8 g of bacterial N/kg of OM truly digested). Results from this experiment indicate that NDSF from citrus pulp can provide similar sources of energy compared with starch from hominy feed to support ruminal microbial growth.

Animal Feed↗
PubMed2000

Involvement of multiple intracellular release channels in calcium sparks of skeletal muscle.

In many types of muscle, intracellular Ca(2+) release for contraction consists of brief Ca(2+) sparks. Whether these result from the opening of one or many channels in the sarcoplasmic reticulum is not known. Examining massive numbers of sparks from frog skeletal muscle and evaluating their Ca(2+) release current, we provide evidence that they are generated by multiple channels. A mode is demonstrated in the distribution of spark rise times in the presence of the channel activator caffeine. This finding contradicts expectations for single channels evolving reversibly, but not for channels in a group, which collectively could give rise to a stereotyped spark. The release channel agonists imperatoxin A, ryanodine, and bastadin 10 elicit fluorescence events that start with a spark, then decay to steady levels roughly proportional to the unitary conductances of 35%, 50%, and 100% that the agonists, respectively, promote in bilayer experiments. This correspondence indicates that the steady phase is produced by one open channel. Calculated Ca(2+) release current decays 10- to 20-fold from spark to steady phase, which requires that six or more channels be open during the spark.

Animals↗
PubMed2000

Comparison of microbial populations in model and natural rumens using 16S ribosomal RNA-targeted probes.

A model rumen system, dual-flow continuous culture fermenters, was evaluated by two comparative criteria in two experiments using ribosomal (r)RNA-targeted DNA probes to compare key microbial groups in samples. The initial experiment measured temporal changes in population structure during adaptation of ruminal microbial populations in fermenters over 240 h. The fermenter inoculum contained 34.9% Bacteria, 60.1% Eukarya and 6.8% Archaea measured as a fraction of total small subunit (SSU) rRNA quantified using a universal probe. The cellulolytic bacterial genus Fibrobacter comprised 9.5% of total SSU rRNA in the inoculum. After 240 h of fermenter operation, the average abundance was 80.9% Bacteria, 6.1% Eukarya, 5.1% Archaea and Fibrobacter genus accounted for 6.6% of the total SSU rRNA. Divergence between ruminal and fermenter population structure was evaluated in the second experiment and samples were classified as ruminal, inoculum or fermenter (96, 120, 144 and 168 h of fermenter operation). Fermenter samples had higher relative abundances of Bacteria (84.5%) and Archaea (2.1%) and lower relative abundances of Eukarya (1.8%) than ruminal samples (average 48.0% Bacteria, 1.3% Archaea and 61.5% Eukarya). The relative abundance of Fibrobacter was similar in all samples, averaging 2.5%. The ruminal and fermenter samples had similar proportions of F. succinogenes and F. succinogenes subgroup 3 (as a percentage of Fibrobacter SSU rRNA). Fibrobacter succinogenes subgroup 1 and F. intestinalis proportions of Fibrobacter were lower in fermenter samples (8.2% and 0.7% respectively) than in ruminal samples (28.4% and 2.2% respectively). Fermenters were able to maintain a core prokaryotic community structure similar to the native microbial community in the rumen. Although protozoa populations were lost, maintenance of Fibrobacter and archaeal populations indicated that the model system supported a functional community structure similar to the rumen. This model rumen system may serve as a suitable tool for studying aspects of ruminal microbial ecology and may resolve some of the relationships between microbial community structure and function by providing control of experimental conditions.

Animals↗
PubMed2000

Protective effects of low and high doses of cyclosporin A against reoxygenation injury in isolated rat cardiomyocytes are associated with differential effects on mitochondrial calcium levels.

In this study we aimed to determine the concentration range of cyclosporin A (CsA) which was effective in protecting against reoxygenation injury in isolated cardiomyocytes, and its effects on intramitochondrial free calcium levels ([Ca2+]m). We also determined whether a high [CsA] had any deleterious effect on normal myocyte function. Isolated adult rat ventricular myocytes were placed in a chamber on the stage of a fluorescence microscope for induction of hypoxia. [Ca2+]m was determined from indo-1/am loaded cells where the cytosolic fluorescence signal had been quenched by superfusion with Mn2+. Cell length was measured using an edge-tracking device. Upon induction of hypoxia, control cells underwent rigor-contracture in 37 +/- 1 min (n = 99) (T1); CsA had no effect on T1. The percentage of control cells which recovered upon reoxygenation depended on the time spent in rigor (T2). With a T2 of 21-30 min, only 36% of control cells recovered compared with 90% and 78% of cells treated with 0.2 microM and 1 microM CsA respectively. After 40 min in rigor, [Ca2+]m was 280 +/- 60 nM in control-recovered cells (50% of cells) and 543 +/- 172 nM and 153 +/- 26 nM in cells treated with 0.2 and 1 microM CsA, respectively (all CsA treated cells recovered). In normoxic studies, CsA had no effect on cell contractility or [Ca2+]m upon rapid pacing, even in presence of an elevated external [Ca2+]. In conclusion, both low and high [CsA] protected against reoxygenation injury to cardiomyocytes despite having opposing effects on [Ca2+]m, suggesting more than one mechanism of action. CsA had no effect on either cell contractility or [Ca2+]m in normoxic cells.

Animals↗
PubMed2000

The spark and its ember: separately gated local components of Ca(2+) release in skeletal muscle.

Amplitude, spatial width, and rise time of Ca(2+) sparks were compared in frog fast-twitch muscle, in three conditions that alter activation of release channels by [Ca(2+)]. A total of approximately 17,000 sparks from 30 cells were evaluated. In cells under voltage clamp, caffeine (0.5 or 1 mM) increased average spark width by 28%, rise time by 18%, and amplitude by 7%. Increases in width were significant even among events of the same rise time. Spontaneous events recorded in permeabilized fibers with low internal [Mg(2+)] (0.4 mM), had width and rise times greater than in reference, and not significantly different than those in caffeine. The spark average in reference rides on a continuous fluorescence "ridge" and is continued by an "ember," a prolongation of width approximately 1 microm and amplitude <0.2, vanishing in approximately 100 ms. Ridge and ember were absent in caffeine and in permeabilized cells. Exposure of voltage-clamped cells to high internal [Mg(2+)] (7 mM) had effects opposite to caffeine, reducing spark width by 26% and amplitude by 27%. In high [Mg(2+)], the ember was visible in individual sparks as a prolongation of variable duration and amplitude up to 1.2. Based on simulations and calculation of Ca(2+) release flux from averaged sparks, the increase in spark width caused by caffeine was interpreted as evidence of an increase in radius of the release source-presumably by recruitment of additional channels. Conversely, spark narrowing suggests loss of contributing channels in high Mg(2+). Therefore, these changes in spark width at constant rise times are evidence of a multichannel origin of sparks. Because ridge and ember were reduced by promoters of Ca(2+)-dependent activation (caffeine, low [Mg(2+)]) and became more visible in the presence of its inhibitors, they are probably manifestations of Ca(2+) release directly operated by voltage sensors.

Animals↗
PubMed2000

Voltage-independent changes in L-type Ca(2+) current uncoupled from SR Ca(2+) release in cardiac myocytes.

To determine the effect of voltage-independent alterations of L-type Ca(2+) current (I(Ca)) on the sarcoplasmic reticular (SR) Ca(2+) release in cardiac myocytes, we measured I(Ca) and cytosolic Ca(2+) transients (Ca(i)(2+); intracellular Ca(2+) concentration) in voltage-clamped rat ventricular myocytes during 1) an abrupt increase of extracellular [Ca(2+)] (Ca(o)(2+)) or 2) application of 1 microM FPL-64176, a Ca(2+) channel agonist, to selectively alter I(Ca) in the absence of changes in SR Ca(2+) loading. On the first depolarization in higher Ca(o)(2+), peak I(Ca) was increased by 46 +/- 6% (P < 0.001), but the increases in the maximal rate of rise of Ca(i)(2+) (dCa(i)(2+)/dt(max), where t is time; an index of SR Ca(2+) release flux) and the Ca(i)(2+) transient amplitude were not significant. Rapid exposure to FPL-64176 greatly slowed inactivation of I(Ca), increasing its time integral by 117 +/- 8% (P < 0.001) without significantly increasing peak I(Ca), dCa(i)(2+)/dt(max), or amplitude of the corresponding Ca(i)(2+) transient. Prolongation of exposure to higher Ca(o)(2+) or FPL-64176 did not further increase peak I(Ca) but greatly increased dCa(i)(2+)/dt(max), Ca(i)(2+) transient amplitude, and the gain of Ca(2+) release (dCa(i)(2+)/dt(max)/I(Ca)), evidently due to augmentation of the SR Ca(2+) loading. Also, the time to peak dCa(i)(2+)/dt(max) was significantly increased in the continuous presence of higher Ca(o)(2+) (by 37 +/- 5%, P < 0.001) or FPL-64176 (by 63 +/- 5%, P < 0.002). Our experiments provide the first evidence of a marked disparity between an increased peak I(Ca) and the corresponding SR Ca(2+) release. We attribute this to saturation of the SR Ca(2+) release flux as predicted by local control theory. Prolongation of the SR Ca(2+) release flux, caused by combined actions of a larger I(Ca) and maximally augmented SR Ca(2+) loading, might reflect additional Ca(2+) release from corbular SR.

Animals↗
PubMed2000

Response of nitrogen metabolism in preparturient dairy cows to methionine supplementation.

Three multiparous Holstein cows (607 kg of BW) were surgically prepared with an elevated carotid artery and indwelling catheters in the hepatic, portal, and two mesenteric veins to study the effects of methionine supplementation on amino acid metabolism during the last 2 wk of pregnancy. The study began 15 d before the expected calving date. Dietary treatments were Control (1.53 Mcal NE(l)/kg, 15.6% CP, and 40% ruminally undegradable protein) and Control supplemented with 60 g/d of ruminally protected methionine (MET, supplying 39 g/d of DL-methionine and approximately 18 g/d of methionine available for intestinal absorption). Each cow received both dietary treatments in a crossover design. Cows were fed once daily. After 5 d on treatment, a blood flow marker (para-aminohippurate) was infused into a mesenteric vein, and arterial, portal, and hepatic blood samples were obtained at 0, 2, 6, 12, and 18 h after feeding. Net flux of methionine was calculated as the plasma arteriovenous difference multiplied by plasma flow. Dry matter intake (10.8 kg/d) and portal (824 L/h) and hepatic (995 L/h) plasma flows were not affected (P > .10) by treatment. Arterial plasma concentration of methionine was greater (P = .10) with MET (27.67 microM) than with Control (16.42 microM). Net portal absorption of methionine increased (P = .10) with MET (26.2 g/d) compared with Control (9.5 g/d). The net portal methionine flux was negatively correlated (r = -.59; P < .001) with arterial urea concentrations. Net flux of methionine across splanchnic tissues shifted (P = .06) from a net uptake with Control (4 g/d) to a net output with MET (11 g/d). Therefore, MET increased by 15 g/d the methionine supply to the rest of the body. The net uptake of methionine by splanchnic tissues observed with Control indicated a net mobilization of methionine by peripheral tissues. Results indicate that methionine was the limiting amino acid with Control and that MET was beneficial because it increased methionine supply to peripheral tissues and reduced arterial urea concentrations.

Animal Feed↗
PubMed2000

Nitrogen metabolism of early lactation cows fed diets with two different levels of protein and different amino acid profiles.

Four multiparous Holstein cows (569+/-122 kg) surgically prepared with indwelling catheters in the mesenteric, portal, and hepatic veins and carotid artery were allocated in a 4 x 4 Latin square to determine the effects of dietary crude protein (CP) level and amino acid (AA) profile on N metabolism during early lactation (from 25 to 65 d in milk). Cows received their diets in two equal meals and were milked twice daily. The dietary treatments were: 18% CP with a high (18H) or a low (18L) quality AA profile, and 15% CP with a high (15H) or a low (15L) quality AA profile. The four diets were similar in net energy for lactation (1.75 NEL Mcal/kg) and contained the same amount of RUP (34% of CP). The quality of the AA profile pertained only to the essential AA (EAA), and was assessed by comparison with the EAA profile of casein and considered the potential contribution of EAA from ruminal bacteria. The 18H and 15H diets were supplemented with 50 and 25 g/d of ruminally protected Met, respectively. After 10 d on treatment, a blood flow marker (p-amino-hippurate) was infused into a mesenteric vein, and arterial, portal, hepatic, and mammary blood samples were obtained at 3, 6, and 12 h after feeding. Dry matter intake was similar across treatments (23.4+/-0.5 kg/d). Amino acid oxidation, and consequent urea production, in the liver were numerically greater with the 18% CP rations, and, as a result, arterial urea concentrations were greatest (P < 0.01) with these rations. The amount of total AA extracted by the mammary gland tended to be greater with the H than with the L diets (21.4 vs. 18.2 mmol/ h, respectively). Milk yield tended to be greater (P = 0.16) with the 18H and 15H diets (47.7 and 46.3 kg/d, respectively) compared with the 18L and 15L diets (45.9 and 44.6 kg/d, respectively). Also, milk CP and casein contents were greatest (P = 0.09) with the H diets compared with the L diets. Milk and plasma urea N were greatest (P < 0.01) with the 18% CP diets. The efficiency of N utilization for milk protein synthesis was greatest (P < 0.09) with the 15% CP diets. It is concluded that milk protein production during early lactation is less susceptible to variations in dietary CP contents than variations in the AA profile of the dietary protein.

Amino Acids↗
PubMed1999

Emergence of homeostasis and "noise imprinting" in an evolution model.

Homeostasis, the creation of a stabilized internal milieu, is ubiquitous in biological evolution, despite the entropic cost of excluding noise information from a region. The advantages of stability seem self evident, but the alternatives are not so clear. This issue was studied by means of numerical experiments on a simple evolution model: a population of Boolean network "organisms" selected for performance of a curve-fitting task while subjected to noise. During evolution, noise sensitivity increased with fitness. Noise exclusion evolved spontaneously, but only if the noise was sufficiently unpredictable. Noise that was limited to one or a few stereotyped patterns caused symmetry breaking that prevented noise exclusion. Instead, the organisms incorporated the noise into their function at little cost in ultimate fitness and became totally noise dependent. This "noise imprinting" suggests caution when interpreting apparent adaptations seen in nature. If the noise was totally random from generation to generation, noise exclusion evolved reliably and irreversibly, but if the noise was correlated over several generations, maladaptive selection of noise-dependent traits could reverse noise exclusion, with catastrophic effect on population fitness. Noise entering the selection process rather than the organism had a different effect: adaptive evolution was totally abolished above a critical noise amplitude, in a manner resembling a thermodynamic phase transition. Evolutionary adaptation to noise involves the creation of a subsystem screened from noise information but increasingly vulnerable to its effects. Similar considerations may apply to information channeling in human cultural evolution.

Algorithms↗
PubMed1999

Amplitude distribution of calcium sparks in confocal images: theory and studies with an automatic detection method.

Determination of the calcium spark amplitude distribution is of critical importance for understanding the nature of elementary calcium release events in striated muscle. In the present study we show, on general theoretical grounds, that calcium sparks, as observed in confocal line scan images, should have a nonmodal, monotonic decreasing amplitude distribution, regardless of whether the underlying events are stereotyped. To test this prediction we developed, implemented, and verified an automated computer algorithm for objective detection and measurement of calcium sparks in raw image data. When the sensitivity and reliability of the algorithm were set appropriately, we observed highly left-skewed or monotonic decreasing amplitude distributions in skeletal muscle cells and cardiomyocytes, confirming the theoretical predictions. The previously reported modal or Gaussian distributions of sparks detected by eye must therefore be the result of subjective detection bias against small amplitude events. In addition, we discuss possible situations when a modal distribution might be observed.

Algorithms↗