The CONSORT statement: Progress in clinical research in pediatric surgery.
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Child↗
Biomedical subjects
R L Moss
Publications and source records attributed to R L Moss.
Cooperative mechanisms in the activation dependence of the rate of force development in rabbit skinned skeletal muscle fibers.
Regulation of contraction in skeletal muscle is a highly cooperative process involving Ca(2+) binding to troponin C (TnC) and strong binding of myosin cross-bridges to actin. To further investigate the role(s) of cooperation in activating the kinetics of cross-bridge cycling, we measured the Ca(2+) dependence of the rate constant of force redevelopment (k(tr)) in skinned single fibers in which cross-bridge and Ca(2+) binding were also perturbed. Ca(2+) sensitivity of tension, the steepness of the force-pCa relationship, and Ca(2+) dependence of k(tr) were measured in skinned fibers that were (1) treated with NEM-S1, a strong-binding, non-force-generating derivative of myosin subfragment 1, to promote cooperative strong binding of endogenous cross-bridges to actin; (2) subjected to partial extraction of TnC to disrupt the spread of activation along the thin filament; or (3) both, partial extraction of TnC and treatment with NEM-S1. The steepness of the force-pCa relationship was consistently reduced by treatment with NEM-S1, by partial extraction of TnC, or by a combination of TnC extraction and NEM-S1, indicating a decrease in the apparent cooperativity of activation. Partial extraction of TnC or NEM-S1 treatment accelerated the rate of force redevelopment at each submaximal force, but had no effect on kinetics of force development in maximally activated preparations. At low levels of Ca(2+), 3 microM NEM-S1 increased k(tr) to maximal values, and higher concentrations of NEM-S1 (6 or 10 microM) increased k(tr) to greater than maximal values. NEM-S1 also accelerated k(tr) at intermediate levels of activation, but to values that were submaximal. However, the combination of partial TnC extraction and 6 microM NEM-S1 increased k(tr) to virtually identical supramaximal values at all levels of activation, thus, completely eliminating the activation dependence of k(tr). These results show that k(tr) is not maximal in control fibers, even at saturating [Ca(2+)], and suggest that activation dependence of k(tr) is due to the combined activating effects of Ca(2+) binding to TnC and cross-bridge binding to actin.
Animals↗
PKA accelerates rate of force development in murine skinned myocardium expressing alpha- or beta-tropomyosin.
In myocardium, protein kinase A (PKA) is known to phosphorylate troponin I (TnI) and myosin-binding protein-C (MyBP-C). Here, we used skinned myocardial preparations from nontransgenic (NTG) mouse hearts expressing 100% alpha-tropomyosin (alpha-Tm) to examine the effects of phosphorylated TnI and MyBP-C on Ca2+ sensitivity of force and the rate constant of force redevelopment (k(tr)). Experiments were also done using transgenic (TG) myocardium expressing approximately 60% beta-Tm to test the idea that the alpha-Tm isoform is required to observe the mechanical effects of PKA phosphorylation. Compared with NTG myocardium, TG myocardium exhibited greater Ca2+ sensitivity of force and developed submaximal forces at faster rates. Treatment with PKA reduced Ca2+ sensitivity of force in NTG and TG myocardium, had no effect on maximum k(tr) in either NTG or TG myocardium, and increased the rates of submaximal force development in both kinds of myocardium. These results show that PKA-mediated phosphorylation of myofibrillar proteins significantly alters the static and dynamic mechanical properties of myocardium, and these effects occur regardless of the type of Tm expressed.
Animals↗
Kinetic differences in cardiac myosins with identical loop 1 sequences.
The kinetics of nucleotide turnover vary considerably among isoforms of vertebrate type II myosin, possibly due to differences in the rate of ADP release from the nucleotide binding pocket. Current ideas about likely mechanisms by which ADP release is regulated have focused on the hyperflexible surface loops of myosin, i.e. loop 1 (ATPase loop) and loop 2 (actin binding loop). In the present study, we investigated the kinetic properties of rat and pig beta-myosin heavy chains (beta-MHC) in which we have found the sequences of loop 1 (residues 204-216) to be virtually identical, i.e. DQSKKDSQTPKG, with a single conservative substitution (rat E210D pig). Pig myocardium normally expresses 100% beta-MHC, whereas rat myocardium was induced to express 100% beta-MHC by surgical thyroidectomy and subsequent treatment with propylthiouracil. Slack test measurements at 15 degrees C yielded unloaded shortening velocities of 1.1 +/- 0.8 muscle lengths/s in rat skinned ventricular myocytes and 0.35 +/- 0.05 muscle lengths/s in pig skinned myocytes. Similarly, solution measurements at the same temperature showed that actin-activated ATPase activity was 2.9-fold greater for rat beta-myosin than for pig beta-myosin. Stopped-flow methods were then used to assess the rates of acto-myosin dissociation by MgATP both in the presence and absence of MgADP. Although the rates of MgATP-induced dissociation of acto-heavy meromyosin (acto-HMM) were virtually identical for the two myosins, the rate of ADP dissociation was approximately 3.8-fold faster for rat beta-myosin (135 s(-)(1)) than for pig beta-myosin (35 s(-)(1)). ATP cleavage rates were nearly 30% faster for rat beta-myosin. Thus, whereas loop 1 appears from other studies to be involved in nucleotide turnover in the pocket, our results show that loop 1 does not account for large differences in turnover kinetics in these two myosin isoforms. Instead, the differences appear to be due to sequence differences in other parts of the MHC backbone.
Amino Acid Sequence↗
Strongly binding myosin crossbridges regulate loaded shortening and power output in cardiac myocytes.
This study investigated the possible roles of strongly binding myosin crossbridges in determining loaded shortening and power output in cardiac myocytes. Single skinned cardiac myocytes were attached between a force transducer and position motor, and shortening velocities were measured over a range of loads during varying levels of Ca(2+) activation. Lowering the [Ca(2+)] slowed shortening velocities, decreased relative power output, and increased the curvature of length traces. We tested the hypothesis that Ca(2+) activation dependence of loaded shortening is determined primarily by strongly binding crossbridges or by [Ca(2+)] per se, which was done by measuring loaded shortening before and after addition of N-ethylmaleimide-conjugated myosin subfragment-1 (NEM-S1), a strongly binding myosin analogue that cooperatively enhances thin filament activation. At fixed [Ca(2+)], NEM-S1 reduced the curvature of length traces and sped loaded shortening velocities. Even when [Ca(2+)] was adjusted so that force was equal with and without NEM-S1, myocyte shortening was faster and exhibited less curvature with NEM-S1. In the presence of NEM-S1, peak relative power output was also significantly greater during activations either at the same [Ca(2+)] or when [Ca(2+)] was adjusted to achieve the same force. Consequently, NEM-S1 eliminated any Ca(2+) dependence of relative power output that is normally observed in cardiac myocytes. These results indicate that strongly binding crossbridges play a significant role in determining loaded shortening and power output and suggest that previously observed Ca(2+) dependence of power output is mediated by alterations in numbers of crossbridges bound to the thin filament.
Animals↗
A subset of periglomerular neurons in the rat accessory olfactory bulb may be excited by GABA through a Na(+)-dependent mechanism.
The periglomerular (PG) cells of the accessory olfactory bulb (AOB) are GABAergic interneurons which receive input from the vomeronasal sensory neurons and form dendrodendritic synapses with each other and with mitral cells. Their electrophysiological properties have not been investigated. We have developed a novel method of isolating PG cells from the AOB, and used the whole-cell patch and gramicidin-perforated patch clamp techniques to measure their basic electrophysiological characteristics and their response to GABA. PG cells were found to be excitable neurons with voltage-gated Na(+) and K(+) currents, though it was very difficult to get PG cells to fire an action potential. The voltage-gated Na(+) currents of PG cells activate at more positive potentials than those of typical CNS neurons. PG cells respond to GABA with currents in which GABA(A) receptors play a significant role. A subset ( approximately 40%) of PG cells respond to GABA with currents which have unusually high reversal potentials, indicating that GABA may be excitatory to these neurons. This phenomenon cannot be explained entirely by elevation of intracellular chloride concentrations, and is dependent on the presence of extracellular sodium.
Action Potentials↗
A thixotropic effect in contracting rabbit psoas muscle: prior movement reduces the initial tension response to stretch.
Paired ramp stretches and releases ('triangular length changes', typically 0.04 +/- 0.09L0 s-1; mean +/- s.e.m.) were imposed on permeabilised rabbit psoas fibre segments under sarcomere length control. In actively contracting fibres, the tension response to stretch was biphasic; tension rose more rapidly during the first 0. 005L0 of the imposed stretch than thereafter. Tension also dropped in a biphasic manner during shortening, and at the end of the length change was reduced below the steady state. If a second triangular length change was imposed shortly after the first, tension rose less sharply during the initial phase of lengthening, i.e. the stiffness of the muscle during the initial phase of the response was reduced in the second stretch. This is a thixotropic effect. If a third triangular length change was imposed on the muscle, the response was the same as that to the second. The time required to recover the original tension response was measured by varying the interval between triangular length changes. Recovery to steady state occurred at a rate of approximately 1 s-1. The stiffness of the muscle during the initial phase of the response scaled with the developed tension in pCa (= -log10[Ca2+]) solutions ranging from 6.3 (minimal activation) to 4.5 (saturating effect). The relative thixotropic reduction in stiffness measured using paired length changes was independent of the pCa of the activating solution. The thixotropic behaviour of contracting skeletal muscle can be explained by a cross-bridge model of muscle contraction in which the number of attached cross-bridges is temporarily reduced following an imposed movement.
Animals↗
Enhanced myosin function due to a point mutation causing a familial hypertrophic cardiomyopathy.
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Actins↗
Rational treatment of empyema in children.
HYPOTHESIS: Efficacious and cost-effective treatment of pediatric empyema can be accomplished following a protocol based on its radiographic appearance. Therapeutic modalities include thoracostomy tube drainage (TTD) with or without fibrinolytic therapy (FT) and video-assisted thoracoscopic debridement (VATD). DESIGN: Retrospective case series. SETTING: Tertiary referral center. RESULTS: From 1995 through 1999, 31 children were treated ranging in age from 11 months to 18 years (mean age, 5.1 years). Twenty-seven (87.1%) underwent TTD; of these, 22 (81.5%) received FT with urokinase. The TTD failed in 4 children (14.8%) who required salvage VATD. Primary VATD was performed in another 4 children (12.9%). The mean length of stay was 14.6 days (TTD, 14.1 days; salvage VATD, 20. 0 days; primary VATD, 11.5 days), ranging from 8.0 to 30.0 days. Complications included readmission for fever (2 patients [6.5%]) and gastrointestinal bleeding (1 patient [3.2%]). There were no anaphylactic reactions or bleeding episodes due to urokinase. Two patients (7.4%) treated with TTD and FT developed an air leak that resolved spontaneously. The mean hospital charges were $78,832 (TTD with or without FT, $75,450; salvage VATD, $107,476; primary VATD, $69,634). The procedural charges were highest for salvage VATD. CONCLUSIONS: Most cases of pediatric empyema can be treated by TTD with or without FT. This therapy is safe and effective for children with nascent disease. Primary VATD is preferred in children with advanced disease. Cost-effectiveness could be further improved through better prediction of those patients likely to fail TTD and require salvage VATD. An algorithmic approach based on findings from computed tomography or (better) ultrasonography of the chest may be the best way to make this distinction and rationalize care.
Adolescent↗
Metastatic appendiceal carcinoid tumor in a child.
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Appendectomy↗
Meconium diseases in infants with very low birth weight.
Retained meconium resulting in intestinal obstruction in infants with very low birth weight (VLBW) may cause significant morbidity and even mortality. Immature intestinal neuromuscular function, abnormal meconium composition, and maternal magnesium sulfate therapy results in delay of first meconium passage. This "normal" passage of first meconium may not occur until 1 week of life or later. A spectrum of conditions results from this delayed passage. At the most serious end of this continuum is intestinal obstruction. These patients present with abdominal distension, emesis, and reduced stool frequency. Early diagnosis of this condition using plain abdominal radiographs and contrast enemas where appropriate is imperative. Contrast enemas may be both diagnostic and therapeutic. Most patients do not need surgical intervention. Operation is indicated when enemas fail to relieve the obstruction or perforation occurs. Prompt diagnosis and appropriate management results in a good outcome. Meconium obstruction in VLBW infants does not appear to be associated with cystic fibrosis or Hirschsprung's disease.
Humans↗
Salvage laparotomy for failure of peritoneal drainage in necrotizing enterocolitis in infants with extremely low birth weight.
BACKGROUND/PURPOSE: Peritoneal drainage is a temporizing procedure for infants with extremely low birth weight (ELBW) who have perforated necrotizing enterocolitis (NEC). "Salvage" laparotomy is advocated when patients worsen after drainage. Some patients have survived with intact gastrointestinal functional after drainage alone. The purpose of this study is to determine if these salvage laparotomies are beneficial. METHODS: The authors reviewed the records of ELBW infants treated at Stanford University with perforated NEC from 1993 through 1998. Data collected included demographic makeup, type of operation, survival rate, postoperative complications, length of stay (LOS), and cost. RESULTS: The authors treated 26 patients, 9 with laparotomy and 17 with peritoneal drainage. The peritoneal drainage group had lower birth weight and more comorbid conditions. Survival rate was similar between laparotomy and drainage: 55.6% versus 41.2%. Four patients in the drainage group underwent salvage laparotomy for perceived clinical deterioration. All of these patients died. The clinical status of patients who had salvage laparotomy and died was similar to those who did not and lived. Seven of 13 patients treated with drainage followed only by supportive care and antibiotics survived. Cost and LOS for patients undergoing salvage laparotomy were much greater than for nonsurviving patients undergoing only peritoneal drainage: 84 +/- 20 days and $660,000 compared with 34 +/- 11 days and $306,000. CONCLUSIONS: Both primary peritoneal drainage and laparotomy should be considered primary therapy for perforated NEC. Patients undergoing peritoneal drainage typically experience clinical deterioration after operation. In this limited experience, salvage laparotomy did not appear beneficial.
Drainage↗
A classification schema for the vomeronasal organ in humans.
The vomeronasal organ is a chemoreceptive structure located at the base of the nasal septum with direct axonal connections to the accessory olfactory bulb in many terrestrial vertebrates. Pheromones presumably bind to the vomeronasal organ and exert behavioral or physiologic responses, thereby allowing chemical communication between animals of the same species. The presence and function of the vomeronasal organ in humans is debated. A phenotypic classification schema for the human vomeronasal organ is described and applied to 253 human subjects who underwent nasal examination. Of these subjects, only 6 percent possessed a vomeronasal organ with 64 percent unilateral and 36 percent bilateral in appearance. No difference existed in gender, age, or race between those subjects with or without a vomeronasal organ. There is no evidence supporting involutional senescence of this structure. Future investigations should use this phenotypic schema for the vomeronasal organ to allow accurate comparisons of study populations.
Adolescent↗
Polyamines decrease Ca(2+) sensitivity of tension and increase rates of activation in skinned cardiac myocytes.
Owing in part to their interactions with membrane proteins, polyamines (e.g., spermine, spermidine, and putrescine) have been identified as potential modulators of membrane excitability and Ca(2+) homeostasis in cardiac myocytes. To investigate whether polyamines also affect cardiac myofilament proteins, we assessed the effects of polyamines on contractility using rat myocytes and trabeculae that had been permeabilized with Triton X-100. Spermine, spermidine, and putrescine reversibly increased the [Ca(2+)] required for half-maximal tension (i.e., right-shifted tension pCa curves), with the following order of efficacy: spermine (+4) > spermidine (+3) > putrescine (+2). However, synthetic analogs that differed from spermine in charge distribution were not as effective as spermine in altering isometric tension. None of the polyamines had a significant effect on maximal tension, except at high concentrations. After flash photolysis of DM-Nitrophen (a caged Ca(2+) chelator), spermine accelerated the rate of tension development at low and intermediate but not high [Ca(2+)]. These results indicate that polyamines, especially spermine, interact with myofilament proteins to reduce apparent Ca(2+) binding affinity and speed cross-bridge cycling kinetics at submaximal [Ca(2+)].
Adenosine Triphosphate↗
The role of magnetic resonance imaging in necrotizing enterocolitis.
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Colon↗
Cytochrome P450 and steroid hydroxylase activity in mouse olfactory and vomeronasal mucosa.
The aims of this study are to identify the sex steroid-metabolizing cytochrome P450 enzymes of the vomeronasal organ (VNO) and to determine the activities of VNO microsomes to metabolize estradiol, progesterone, and testosterone. Several P450 isoforms, including CYP1A2, CYP2A, CYP2B, CYP2C, CYP2G1, and CYP3A, NADPH P450-reductase, and microsomal epoxide hydrolase were detected in mouse VNO, although their expression levels were much lower than those in the main olfactory epithelium. VNO microsomes were active toward the three steroid hormones, producing metabolite profiles similar to those seen with olfactory mucosal microsomes. Thus, the mammalian VNO, a steroid hormone target tissue, contains multiple steroid-metabolizing P450 isoforms and is capable of metabolic disposition of the three major sex steroid hormones. These findings support the proposed roles of olfactory mucosal and VNO microsomal P450 enzymes in maintaining cellular hormonal homeostasis and other perireceptor processes associated with olfactory chemosensory function.
Animals↗
Functional dichotomy within the vomeronasal system: distinct zones of neuronal activity in the accessory olfactory bulb correlate with sex-specific behaviors.
Chemosensory neurons in the vomeronasal organ (VNO) detect pheromones that elicit social and reproductive behaviors in most terrestrial vertebrates. Vomeronasal receptor neurons are chemoarchitecturally divided into two populations based on their position in the VNO, the type of G-protein subunit expressed, the family of putative pheromone receptor expressed, and termination site of their axons in the accessory olfactory bulb (AOB). To investigate the functional implications of these two segregated VNO-AOB pathways, we stimulated mice with pheromonal cues associated with different behavioral contexts and examined cellular activation patterns in the AOB. Exposure of ICR male mice to BALB/c males resulted in aggressive behavior, accompanied by a VNO-dependent increase in c-fos immunoreactivity in a cluster of cells located almost exclusively in the caudal AOB in both strains. This caudal cluster of activated cells did not appear to require the overt display of aggressive behavior because it was present in both the dominant and submissive males and could be evoked when the stimulus animal was anesthetized. In contrast, exposure of an ICR male to an ICR female in diestrus resulted in activation of cells located predominantly in the rostral AOB. Our findings indicate that male-to-male interactions involving interstrain recognition activate a separate population of vomeronasal receptor neurons than chemosensory cues detected in a sexual context. The results suggest that the dichotomy in the peripheral vomeronasal system serves to separate pheromones based on the behaviors they drive. As such, the results provide a bioassay for identifying pheromone molecules.
Aggression↗
Impaired cardiomyocyte relaxation and diastolic function in transgenic mice expressing slow skeletal troponin I in the heart.
1. To assess the specific functions of the cardiac isoform of troponin I (cTnI), we produced transgenic mice that expressed slow skeletal troponin I (ssTnI) specifically in cardiomyocytes. Cardiomyocytes from these mice displayed quantitative replacement of cTnI with transgene-encoded ssTnI. 2. The ssTnI transgenic mice were viable and fertile and did not display increased mortality or detectable cardiovascular histopathology. They exhibited normal ventricular weights and heart rates. 3. Permeabilized transgenic cardiomyocytes demonstrated an increased Ca2+ sensitivity of tension and a lack of contractile responsiveness to cAMP-dependent protein kinase (PKA). Isolated cardiomyocytes from transgenic mice had normal velocities of unloaded shortening but unlike wild-type controls exhibited no enhancement of the velocity of shortening in response to treatment with isoprenaline. Transgenic cardiomyocytes exhibited greater extents of shortening than non-transgenic cardiomyocytes at baseline and after treatment with isoprenaline. 4. The rates of rise of intracellular [Ca2+] and the peak amplitudes of the intracellular [Ca2+] transients were similar in transgenic and wild-type myocytes. However, the half-time of intracellular [Ca2+] decay was significantly greater in the transgenic myocytes. This change in decay of intracellular [Ca2+] was correlated with an increase in the re-lengthening time of the transgenic cells. 5. These changes in cardiomyocyte function in vitro were manifested in vivo as impaired diastolic function both at baseline and after stimulation with isoprenaline. 6. Thus, cTnI has important roles in regulating the Ca2+ sensitivity of cardiac myofibrils and controlling cardiomyocyte relaxation and cardiac diastolic function. cTnI is also required for the normal responsiveness of cardiomyocytes to beta-adrenergic receptor stimulation.
Animals↗