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Biomedical subjects

R L Moss

Publications and source records attributed to R L Moss.

At least 19 recordsLinked to original sources
PubMed1997

Ca2+ binding to troponin C in skinned skeletal muscle fibers assessed with caged Ca2+ and a Ca2+ fluorophore. Invariance of Ca2+ binding as a function of sarcomere length.

Ca2+ sensitivity of tension varies with sarcomere length in both skeletal and cardiac muscles. One possible explanation for this effect is that the Ca2+ affinity of the regulatory protein troponin C decreases when sarcomere length is reduced. To examine length dependence of Ca2+ binding to troponin C in skeletal muscle, we developed a protocol to simultaneously monitor changes in sarcomere length, tension, and Ca2+ concentration following flash photolysis of caged Ca2+. In this protocol, [Ca2+] was rapidly increased by flash photolysis of caged Ca2+, and changes in [Ca2+] due to photolysis and the subsequent binding to troponin C were assessed using a Ca2+ fluorophore. Small bundles of fibers from rabbit skinned psoas muscles were loaded with Ca2+ fluorophore (Fluo-3) and caged Ca2+ (dimethoxynitrophenamine or o-nitrophenyl-EGTA). The bundles were then transferred to silicone oil, where [Ca2+]free, tension, and sarcomere length were monitored before and after photolysis of caged Ca2+. Upon photolysis of caged Ca2+, fluorescence increased and then decayed to a new steady-state level within approximately 1 s, while tension increased to a new steady-state level within approximately 1.5 s. After extracting troponin C, fibers did not generate tension following the flash, but steady-state post-flash fluorescence was significantly greater than when troponin C was present. The difference in [Ca2+]free represents the amount of Ca2+ bound to troponin C. In fibers that were troponin C-replete, Ca2+ binding to troponin C did not differ at short (approximately 1.97 microm) and long (approximately 2.51 microm) sarcomere length, yet tension was approximately 50% greater at the long sarcomere length. These results show that the affinity of troponin C for Ca2+ is not altered by changes in sarcomere length, indicating that length-dependent changes in Ca2+ sensitivity of tension in skeletal muscle are not related to length-dependent changes in Ca2+ binding affinity of troponin C.

Aniline Compounds↗
PubMed1996

Contractile properties and protein isoforms of single fibres from the chicken pectoralis red strip muscle.

1. The contractile properties of single muscle fibres of the red strip region of adult chicken pectoralis major (PM) muscle, some of which are known to express an embryonic isoform of myosin heavy chain (MHC), were determined and compared with the properties of the fast white fibres of the PM and the slow tonic fibres of the anterior latissimus dorsi (ALD) muscle. 2. The red strip fibres could be classified into two groups, fast and slow. The mean velocity of unloaded shortening (Vmax) in fast red strip fibres was approximately half the Vmax of fast white fibres. Vmax of slow red strip fibres was less than 20% of the value for fast red strip fibres and was not different from Vmax of ALD fibres. 3. The tension-generating ability, i.e. the maximal isometric tension/fibre cross-sectional area (P0/CSA), was the same in fast red strip fibres and fast white fibres. P0/CSA was approximately 30% lower in slow red strip fibres compared with fast red strip fibres but was 70% greater in slow red strip fibres compared with ALD fibres. 4. The tension-pCa relation of fast red strip fibres was shifted to lower pCa values, indicating a lower calcium sensitivity compared with fast white fibres, and this difference was associated with a difference in troponin T isoform composition. The tension-pCa relation of slow red strip fibres was not different from that in ALD fibres. 5. The difference in Vmax between fast red strip fibres and fast white fibres was associated with different MHC compositions of these fibres. 6. The myofibrillar protein isoform composition of slow red strip fibres was identical to that of the slow tonic fibres of ALD muscle and these two groups of fibres had very similar contractile properties.

Animals↗
PubMed1996

17 beta-Estradiol potentiates kainate-induced currents via activation of the cAMP cascade.

Evidence for nongenomic actions of steroids is now coming from a variety of fields of steroid research. Mechanisms of steroid action are being studied with regard to the membrane receptors and the activation of second messengers. The present study investigated the mechanism for the rapid effect of estrogen on acutely dissociated hippocampal CA1 neurons by using the whole-cell, voltage-clamp recording. Under the perforated patch configuration, 17 beta-estradiol potentiated kainate-induced currents in 38% of tested neurons. The potentiation was stereospecific, rapid in onset, and reversible after the removal of the steroid. Dose-response curves show that the potentiation by 17 beta-estradiol was evident at a concentration as low as 10 nM and saturated at 10 microM. 17 beta-Estradiol did not affect the kinetics (i.e., affinity and cooperativity) and reversal potential of kainate-induced currents. This suggests that the potentiation did not result from direct interaction with kainate receptors nor the activation of ion channels other than kainate receptor-channels. The potentiation by 17 beta-estradiol was similar to the enhancement of kainate-induced currents evoked by 8-bromo-cAMP, and was modulated by an inhibitor of phosphodiesterase (IBMX). The estrogen potentiation was blocked by a specific blocker of PKA (Rp-cAMPS). Under standard recording configuration, the effect was significantly affected by intracellular perfusing with GDP-beta-S or GTP-gamma-S. The data suggest that the potentiation of kainate-induced currents by 17-beta-estradiol was likely a G-protein(s) coupled, cAMP-dependent phosphorylation event. By involvement of this non-genomic mechanism, estrogen may play a role in the modulation of excitatory synaptic transmission in the hippocampus.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1996

Onset of reduced Ca2+ sensitivity of tension during stunning in porcine myocardium.

Recent data suggest that reduced Ca2+ sensitivity of tension is a mechanism of the post-ischemic myocardial dysfunction, termed stunning. The purpose of the present study was to determine whether the decrease in myofilament Ca2+ sensitivity occurs during ischemia or during the subsequent period of reperfusion. Serial biopsies from an in vivo open-chest porcine model of regional LAD myocardial stunning (n = 6) were used to obtain in vitro measurements of Ca2+ sensitivity of tension in myocardium from the LAD bed. Regional ventricular myocardial function was assessed from percentage systolic myocardial wall thickening (%Th) and the load-independent end-systolic pressure wall thickness relation (ESPTR). Stunning was induced by 45 min of low flow LAD ischemia (43 +/- 4 ml/min/100 gm) followed by 30 min of reperfusion with control aerobic flow (117 +/- 7 ml/min/100 g). Endocardial biopsies were obtained from the LAD bed during pre-ischemia, ischemia (immediately prior to reperfusion), and post-ischemia (after 30 min of reperfusion). Biopsies were mechanically disrupted and single cell-sized preparations of permeabilized myocardium were attached to a force transducer to measure directly steady-state tension-pCa relationships. The % decreased to 7 +/- 11% of control during ischemia (P < 0.001) and returned to 30 +/- 11% of control in the post-ischemic stunned state (P < 0.001). Stunning resulted in a significant leftward shift of the ESPTR as compared to control, indicating depressed regional myocardial function. The pCa (-log[Ca2+]) for half maximal activation of tension, i.e. pCa50, was 5.96 +/- 0.04 in control myocardium and was unchanged during ischemia (5.95 +/- 0.03), but significantly decreased to 5.82 +/- 0.04 upon reperfusion (P < 0.05). These data show that the decrease in Ca2+ sensitivity of tension associated with stunning occurs during reperfusion, and supports the idea that reperfusion injury is a mechanism of myocardial stunning.

Actin Cytoskeleton↗
PubMed1996

Altered kinetics of contraction in skeletal muscle fibers containing a mutant myosin regulatory light chain with reduced divalent cation binding.

We examined the kinetic properties of rabbit skinned skeletal muscle fibers in which the endogenous myosin regulatory light chain (RLC) was partially replaced with a mutant RLC (D47A) containing a point mutation within the Ca2+/Mg2+ binding site that severely reduced its affinity for divalent cations. We found that when approximately 50% of the endogenous RLC was replaced by the mutant, maximum tension declined to approximately 60% of control and the rate constant of active tension redevelopment (ktr) after mechanical disruption of cross-bridges was reduced to approximately 70% of control. This reduction in ktr was not an indirect effect on kinetics due to a reduced number of strongly bound myosin heads, because when the strongly binding cross-bridge analog N-ethylmaleimide-modified myosin subfragment1 (NEM-S1) was added to the fibers, there was no effect upon maximum ktr. Fiber stiffness declined after D47A exchange in a manner indicative of a decrease in the number of strongly bound cross-bridges, suggesting that the force per cross-bridge was not significantly affected by the presence of D47A RLC. In contrast to the effects on ktr, the rate of tension relaxation in steadily activated fibers after flash photolysis of the Ca2+ chelator diazo-2 increased by nearly twofold after D47A exchange. We conclude that the incorporation of the nondivalent cation-binding mutant of myosin RLC decreases the proportion of cycling cross-bridges in a force-generating state by decreasing the rate of formation of force-generating bridges and increasing the rate of detachment. These results suggest that divalent cation binding to myosin RLC plays an important role in modulating the kinetics of cross-bridge attachment and detachment.

Animals↗
PubMed1996

Calcium alone does not fully activate the thin filament for S1 binding to rigor myofibrils.

Skeletal muscle contraction is regulated by calcium via troponin and tropomyosin and appears to involve cooperative activation of cross-bridge binding to actin. We studied the regulation of fluorescent myosin subfragment 1 (fS1) binding to rigor myofibrils over a wide range of fS1 and calcium levels using highly sensitive imaging techniques. At low calcium and low fS1, the fluorescence was restricted to the actin-myosin overlap region. At high calcium and very low fS1, the fluorescence was still predominantly in the overlap region. The ratio of nonoverlap to overlap fluorescence intensity showed that increases in the fS1 level resulted in a shift in maximum fluorescence from the overlap to the nonoverlap region at both low and high calcium; this transition occurred at lower fS1 levels in myofibrils with high calcium. At a fixed fS1 level, increases in calcium also resulted in a shift in maximum fluorescence from the overlap region to the nonoverlap region. These results suggest that calcium alone does not fully activate the thin filament for rigor S1 binding and that, even at high calcium, the thin filament is not activated along its entire length.

Actins↗
PubMed1996

Necrotizing fasciitis in children: prompt recognition and aggressive therapy improve survival.

UNLABELLED: Necrotizing fasciitis (NF) is a bacterial infection of the soft tissues with a fulminant course and a high mortality rate. The authors performed a review to define the diagnosis, bacteriology, and management of NF in the pediatric population. This report of 20 cases treated over 18 years represents the largest reported pediatric experience. These infections were attributable to secondary infection of varicella lesions (5), omphalitis (4), extremity lesions (4), perineal infections (3), head and neck lesions (2), inguinal herniorrhapy (1), and breast abscess (1). Nineteen of the 20 children were healthy, without chronic disease or immunosuppression. All patients presented with an altered sensorium and signs of systemic toxicity. Fever (40%), tachycardia (70%), and abnormal white blood cell count (50%) were not uniformly present. There was marked tissue edema in all patients, with a characteristic peau d'orange appearance in 18. Seven infections were caused by streptococcus; the remainder were polymicrobial, involving multiple aerobes and anaerobes. Initial gram stain was of limited utility; in 14 of 19 cases the result was negative or showed only one of many organisms present. Fifteen patients survived and five died. All survivors underwent aggressive surgical debridement within 3 hours of admission. The survivors required of a mean of 3.8 operations. Fascial excision of up to 35% of total body surface area was required. One patient required amputation, two had colostomies, and six required extensive skin grafting for reconstruction. All five patients who died had delayed initial management. CONCLUSION: NF is a serious cause of death in previously healthy children. The diagnosis should be considered in the presence of any soft tissue infection presenting with signs of toxicity and marked wound edema, even in the absence of fever or abnormal white blood cell count. Immediate surgical debridement and coverage with penicillin, an aminoglycoside, and metronidazole are essential. Subsequent changes in antibiotics should be based on culture data because gram stain results are not reliable. More than one operation is required in almost all cases.

Adolescent↗
PubMed1996

Clinical judgment is superior to diagnostic tests in the management of pediatric small bowel injury.

Traumatic solid organ injuries are easily recognizable on computed tomography (CT) scans and usually are treated nonoperatively. Small bowel injuries may be difficult to diagnose and require prompt operation. This study was done to assess the role of clinical examination versus diagnostic tests in evaluating these injuries. The medical records of all pediatric (< or = 18 years old) patients treated at a pediatric trauma center from 1984 to 1995 were reviewed. Statistical analysis was performed using SAS software, with P values of less than .05 considered significant. Small bowel injury occurred in 48 patients (21 blunt, 27 penetrating). Most blunt injuries were automobile-related (11 patients) or attributable to recreational activities (4) or bicycle accidents (2). Penetrating injuries were primarily caused by assaults with guns (21) or knives (4). All conscious patients with small bowel injury had abnormal physical examination findings at the time of presentation. Nineteen patients had generalized peritonitis, and 14 had localized abdominal tenderness. The serum amylase level was abnormal in 2 of 18 cases. Abdominal CT scans were obtained in six patients and showed the injury in only three. Peritoneal lavage (DPL), performed in 10 patients, led to the diagnosis in five. There was no significant difference in the complication rate (30%) between patients operated on immediately because of a diagnostic test result and those operated on later, after a period of clinical observation (P = 1.0, Fisher's Exact test). Associated injuries were common (60%) among both blunt and penetrating cases. In this nonoperative era of pediatric trauma care, small bowel injury is best diagnosed clinically. The physical examination is 100% sensitive in the conscious patient, and specificity is achieved by serial examination. Serum amylase, CT scan, and DPL are not reliable diagnostic tests to exclude these injuries. Patients can be observed until physical findings suggest bowel injury without increased morbidity. Associated injuries are common; thus, patients are best treated where multidisciplinary support is available.

Adolescent↗
PubMed1996

Pancreatitis caused by a gastric duplication communicating with an aberrant pancreatic lobe.

Developmental anomalies of the pancreas and its ductal drainage system are an important cause of pancreatitis. Patients with such anomalies require appropriate surgical intervention. This report concerns an uncommon foregut anomaly that causes pancreatitis. A 9-year-old girl had recurrent pancreatitis secondary to a gastric duplication communicating with an aberrant pancreatic lobe. Appreciation of the relevant anatomy led to successful surgical management of the pancreatitis.

Anastomosis, Roux-en-Y↗
PubMed1996

Microgastria as an isolated anomaly.

The authors report the case of an 8-year-old boy who had isolated microgastria. The patient had required lifelong jejunal tube feeding because of inadequate gastric volume and intractable gastroesophageal reflux. Gastric augmentation was performed with a Roux-en-Y jejunal reservoir (Hunt-Lawrence pouch), with good results.

Anastomosis, Roux-en-Y↗
PubMed1996

Necrotizing enterocolitis and total parenteral nutrition-associated cholestasis.

The proportion of patients with total parenteral nutrition (TPN)-associated cholestasis (TPN-AC) who have necrotizing enterocolitis (NEC) has increased markedly in the past ten years. Little is known about how these diseases affect each other. We retrospectively studied 24 patients with NEC and bowel necrosis or perforation who required surgical intervention. Patients were divided into two groups: those who had received TPN (NEC + TPN, n = 17) and those who had not (NEC, n = 7). As cholestasis was present clinically, or prolonged TPN was anticipated, liver biopsy was done. Bile acid levels were measured in both serum and bile in 13 patients. Six patients, who underwent bowel resection and enterostomy, had a second liver biopsy and measurement of bile acid levels at stoma closure. Our results showed that in 13 patients for whom bile acid levels were measured (NEC + TPN, n = 6) (NEC, n = 7), serum bile acid level was significantly elevated in both groups over normal for age. Biliary bile acid levels were correspondingly depressed in both groups suggesting a failure of bile acid transport. All patients had abnormal liver histology, but the pattern of injury differed between the two groups. Those in the NEC group had biliary stasis and mild hepatocyte degeneration. In contrast, 15 of 17 in the NEC + TPN group had advanced injury specific for TPN-AC. All six patients managed on TPN and partial enteral feeding before a second biopsy had no change in bile acid levels and progression of histologic injury. We conclude that NEC alone can cause functional cholestasis and histologic liver injury but does not cause the specific progressive damage caused by TPN. NEC may make the liver more susceptible to the effects of TPN. Partial enteral feeding does not halt or reverse this injury.

Bile Acids and Salts↗
PubMed1996

Nongenomic actions of estrogen in the brain: physiological significance and cellular mechanisms.

Estrogen regulates neuroendocrine, reproductive, and behavioral functions of the brain by utilizing a number of diverse cellular mechanisms. In the classical genomic mechanism of steroids, estrogen induces relatively long-term actions on neurons by activating specific intracellular receptors that modulate transcription and protein synthesis. In addition, estrogen can also exert very rapid effects in the brain that cannot be attributed to genomic mechanisms. These nongenomic actions of estrogen influence a variety of neuronal properties, including electrical excitability, synaptic functioning, and morphological features, and are involved in many of the physiological functions and clinical effects of estrogen in the brain. Recently the specific cellular and molecular mechanisms underlying the nongenomic actions of estrogen have begun to be elucidated. Estrogen may utilize direct membrane mechanisms, such as activation of ligand-gated ion channels and G-protein-coupled second messenger systems and regulation of neurotransmitter transporters. Additionally the membrane and genomic actions of estrogen have the potential to interact, producing synergistic effects and dependence between the two types of mechanisms. The combination of nongenomic and genomic mechanisms endows estrogen with considerable diversity, range, and power in regulating neural function.

Animals↗
PubMed1996

Signal processing in the vomeronasal system: modulation of sexual behavior in the female rat.

Chemosensory cues detected by the vomeronasal (VN) organ modulate a variety of social interactions in many species. In particular, activation of the VN system by pheromones regulates sexual behavior in the rodent. Although the exact nature of stimulus access to the organ is not clearly defined, the neuroanatomical pathway connecting the VN organ to hypothalamic centers controlling reproductive function is well established and relatively straightforward. Electrophysiological techniques have provided insight into the signal transduction process throughout the VN system. Combining behavioral studies with immunocytochemical detection of immediate early genes and neuropeptides reveals that gonadotropin hormone releasing hormone (GnRH)-containing neurons are specifically activated by stimulation of the VN organ. Furthermore, some of the activated GnRH neurons project to the ventromedial hypothalamus where they are hypothesized to induce sexual responsiveness. Early anecdotal evidence of an influence of the VN organ on human reproductive events has been substantiated by more recent anatomical, behavioral, and electrophysiological studies. Thus, further deciphering of the signal transduction process within the VN system of the rodent may yield unique insights into behaviors associated with human reproduction.

Amygdala↗
PubMed1995

Slowing of shortening velocity of rat cardiac myocytes by adenosine receptor stimulation regardless of beta-adrenergic stimulation.

1. Single ventricular myocytes were enzymatically isolated, incubated with the A1-purinergic and beta-adrenergic receptor-specific agonists N6-cyclopentyladenosine (CPA) and isoprenaline (Iso), and then rapidly skinned. Ca2+ sensitivity of isometric tension and unloaded shortening velocity (Vo) were measured, and protein kinase A (PKA)-specific phosphorylations of troponin I (TnI) and C-protein were assessed by back-phosphorylation of cell suspensions with [gamma-32P]-ATP. 2. Isoprenaline treatment decreased the Ca2+ sensitivity of isometric tension relative to propranolol-treated controls, as did simultaneous stimulation with Iso and CPA (Iso + CPA). CPA alone had no effect on Ca2+ sensitivity. Vo was greater in Iso-treated cells than in paired controls, while Vo was significantly less than control in both Iso + CPA-treated and CPA-treated cells. 3. Phosphorylation of TnI and C-protein was increased by Iso treatment and also when Iso and CPA were simultaneously applied. CPA alone caused a significant decrease in the phosphorylation state of these two proteins. 4. From these results we conclude that A1-purinergic receptor stimulation does not inhibit beta-adrenergic receptor-mediated phosphorylation of myofilament proteins, nor does it alter the Ca2+ sensitivity of isometric tension at the level of the myofilaments. However, A1-receptor stimulation does decrease Vo at the level of the myofilaments by a mechanism that is independent of beta-adrenergically mediated phosphorylation of TnI and C-protein.

Adenosine↗
PubMed1995

In vivo stimulated dopamine release in the nucleus accumbens: modulation by the prefrontal cortex.

In vivo voltammetry was used to measure stimulated dopamine (DA) release in the nucleus accumbens following 6-hydroxydopamine (6-OHDA) lesions of the medial prefrontal cortex (PFC). Lesions of the PFC resulted in a significant potentiation of K(+)-stimulated DA release (383% of control). These data are in agreement with other studies which suggest DAergic activation of cortical sites can alter the activity of DAergic neurons at subcortical sites. Specifically these results suggest that DAergic nerve terminals in the nucleus accumbens are tonically inhibited by DAergic activity in the PFC and that alleviation of this tonic inhibition produces hyperresponsiveness in the nucleus accumbens.

Animals↗
PubMed1995

Electrophysiological evidence for glutamate as a vomeronasal receptor cell neurotransmitter.

Bipolar receptor cells in the vomeronasal organ send axonal projections to the accessory olfactory bulb where they synapse with mitral cell dendrites. Although the nature of the synapse is thought to be excitatory, the neurotransmitter(s) involved has not yet been identified. Electrophysiological recordings of single neurons in the mitral cell layer of the AOB in response to vomeronasal nerve stimulation were conducted to characterize the synaptic response and the underlying neurotransmitter substance. Extracellular activity was recorded in vivo (whole animal) and in vitro (AOB slice) from female rats. In vivo, the predominant response to stimulation of the VNO was excitation. In many instances in the whole animal preparation, the excitation was followed by an inhibitory response. Attempts to block the excitatory response by ejecting kynurenic acid in close proximity to the mitral cell being recorded were not successful. Since this failure may have been due to inability of the antagonist to reach its presumed site of action at the dendrite, further recordings were carried out in vitro. In the AOB slice preparation, the predominant response to stimulation of the VN nerve endings was excitation. Superfusion of the non-NMDA antagonist, CNQX, into the medium resulted in a reduction of the orthodromic excitation in 5 of 8 cells. The NMDA antagonist, AP-5, was found to blunt orthodromic excitation in 1 of 4 cells. These results suggest that the excitatory response evoked in mitral cells followng stimulation of the VN nerve is mediated by glutamate.

2-Amino-5-phosphonovalerate↗
PubMed1995

Length dependence of Ca2+ sensitivity of tension in mouse cardiac myocytes expressing skeletal troponin C.

1. Beat-to-beat performance of myocardium is highly dependent on sarcomere length. The physiological basis for this effect is not well understood but presumably includes alterations in the extent of overlap between thick and thin filaments. Sarcomere length dependence of activation also appears to be involved since length-tension relationships in cardiac muscle are usually steeper than those in skeletal muscle. 2. An explanation recently proposed to account for the difference between length-tension relationships is that the cardiac isoform of troponin C (cTnC) has intrinsic properties that confer greater length-dependent changes in the Ca2+ sensitivity of tension than does skeletal troponin C (sTnC), presumably due to greater length-dependent changes in the Ca(2+)-binding affinity of cTnC. To test this hypothesis, transgenic mice were developed in which fast sTnC was expressed ectopically in the heart. This allowed a comparison of the length dependence of the Ca2+ sensitivity of tension between myocytes having thin filaments that contained either endogenous cTnC or primarily sTnC. 3. In myocytes from both transgenic and normal mice, the Ca2+ sensitivity of tension increased similarly when mean sarcomere length was increased from approximately 1.83 to 2.23 microns. In both cases, the mid-point (pCa50) of the tension-pCa (i.e. -log[Ca2+]) relationship shifted 0.12 +/- 0.01 pCa units (mean +/- S.E.M.) in the direction of lower Ca2+. 4. We conclude that the Ca2+ sensitivity of tension in myocytes changes as a function of sarcomere length but is independent of the isoform of troponin C present in the thin filaments.

Actin Cytoskeleton↗