Plasticity in the dynamics of myocardial contraction: Ca2+, crossbridge kinetics, or molecular cooperation.
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Animals↗
Biomedical subjects
R L Moss
Publications and source records attributed to R L Moss.
What comprises appropriate therapy for children/adolescents with rhabdomyosarcoma arising in the abdominal wall? A report from the Intergroup Rhabdomyosarcoma Study Group.
PURPOSE: The aim of this study was to define clinical features and determine the best therapy for patients with rhabdomyosarcoma (RMS) of the abdominal wall. METHODS: We examined the demographic, clinical features, therapy (especially surgical), and outcome of 34 patients. Patients received combination chemotherapy after complete surgical resection (group I, n = 14; 41%); resection with microscopic residual followed by local irradiation (RT; group II, n = 8; 24%); partial resection or biopsy only plus RT with gross locoregional residual tumor (group III, n = 4; 12%); or biopsy only plus RT with metastatic disease (group IV, n = 8; 24%). Patients with group I or group II tumors had undergone partial abdominal wall resection (ie, involved muscle only with preservation of peritoneum, n = 11) or complete abdominal wall resection (n = 7). Four additional patients had groin lesions. RESULTS: Thirty-four children or adolescents with abdominal wall RMS (about 1% of all patients) were treated on Intergroup Rhabdomyosarcoma Study I (IRS-I) through IRS-IV. Overall, adolescents comprised 14 of 34 eligible patients (41%), and 10 of 14 (71%) adolescents had alveolar or undifferentiated tumors versus 8 of 20 (40%) younger children (P= .07). Failure-free survival (FFS) rate and survival rate at 5 years was 65%. Treatment outcome was poorer for patients with group III-IV tumors (P = .01), adolescents (P = .09) and patients with alveolar or undifferentiated sarcomas (P = .12). CONCLUSION: Patients with localized tumors appear to fare better if they undergo complete abdominal wall resection (long-term survival rate, 100%) versus partial resection (long-term survival rate, 62% [P = .12]).
Abdominal Muscles↗
Activation of an anatomically distinct subpopulation of accessory olfactory bulb neurons by chemosensory stimulation.
Chemosensory cues known as pheromones play a key role in rodent reproductive physiology and social interactions. Pheromone molecules are detected by receptor cells located in the vomeronasal organ and conveyed exclusively to the accessory olfactory bulb, and then to limbic and hypothalamic sites for integration with other factors modulating reproductive physiology. We report here that chemosensory cues from the female mouse selectively activate a subpopulation of cells located in the anterior part of the accessory olfactory bulb of the male mouse. Exposure of male mice to female-soiled bedding resulted in a massive induction of c-fos expression, which was primarily confined to neurons located in the anterior part of the accessory olfactory bulb and was eliminated by removal of the vomeronasal organ. Exposure of the male to soiled bedding from a different stain of male mice also elevated c-fos expression, but immunoreactive cells were more evenly distributed along the anterior-posterior axis of the accessory olfactory bulb. No treatment effects were observed in the main olfactory bulb. Previous studies have indicated that vomeronasal receptor neurons are divided into two populations based on location within the organ, site of termination in the accessory olfactory bulb, second messenger content and putative pheromone receptor expression. The present study suggests that the two populations of vomeronasal receptor neurons detect different chemosensory stimuli. Since male mouse- and female mouse-specific urinary substances modulate different aspects of male mouse behavior, the present results suggest that anatomically segregated populations of vomeronasal organ receptor cells modulate distinct behavioral patterns.
Animals↗
New approaches to understanding the etiology and treatment of total parenteral nutrition-associated cholestasis.
Total parenteral nutrition-associated cholestasis (TPN-AC) may be a fatal disease. The only known effective treatment is to discontinue TPN and institute full enteral feedings. However, this is not possible for many patients with severe gastrointestinal failure. Current research supports two theories regarding the etiology of TPN-AC. One proposes that the enteral fast disrupts the enterohepatic circulation. Cholestasis, in this hypothesis, results from a combination of altered gut hormone production and endotoxins produced by bacterial translocation. The second theory implicates the direct toxicity of TPN solution. Amino acid solutions and plant sterols in intralipid have generated much interest. Ursodeoxycholic acid and S-adenosyl-L-methionine are promising treatments for TPN-AC. They have been proven to be effective in animals and adult liver diseases. Cholecystokinin also has been investigated as a possible prophylactic agent. However, results from these experiments do not conclusively show a beneficial effect.
Animals↗
Nutritional support of the pediatric surgical patient.
This review discusses the important developments in pediatric surgical nutrition over the past year. Sepsis and total parenteral nutrition-associated cholestasis remain complex problems for patients on total parenteral nutrition. Investigations suggest that total parenteral nutrition may compromise bactericidal activity, increasing the risk of sepsis. Sepsis possibly sensitizes the liver to cholestatic injury. Small volume enteral feeds may restore immune system function. Current research does not support an association between phytosterols in parenteral lipid solutions and total parenteral nutrition-associated cholestasis. Methionine has been identified as a potential hepatotoxin. Ursodeoxycholic acid and S-adenosyl-L-methionine are the most promising treatments of total parenteral nutrition-associated cholestasis. Small bowel transplant is now a reasonable option for patients with irreversible intestinal failure. Patient and graft survival rates have improved with FK-506 (Tacrolimus) immunosuppression. Isolated intestinal grafts have the best survival rate (92% at 1 year). Most surviving graft recipients are weaned off of total parenteral nutrition. The Cox Proportional Hazard model may help to identify candidates for small bowel transplant. This equation predicts the duration of dependence on total parenteral nutrition. Patients with irreversible intestinal failure can then be referred for early small bowel transplantation.
Child↗
Altered kinetics of contraction of mouse atrial myocytes expressing ventricular myosin regulatory light chain.
To investigate the role of myosin regulatory light chain isoforms as a determinant of the kinetics of cardiac contraction, unloaded shortening velocity was determined by the slack-test method in skinned wild-type murine atrial cells and transgenic cells expressing ventricular regulatory light chain (MLC2v). Transgenic mice were generated using a 4.5-kb fragment of the murine alpha-myosin heavy chain promoter to drive high levels of MLC2v expression in the atrium. Velocity of unloaded shortening was determined at 15 degrees C in maximally activating Ca2+ solution (pCa 4.5) containing (in mmol/l) 7 EGTA, 1 free Mg2+, 4 MgATP, 14.5 creatine phosphate, and 20 imidazole (ionic strength 180 mmol/l, pH 7.0). Compared with the wild type (n = 10), the unloaded shortening velocity of MLC2v-expressing transgenic murine atrial cells (n = 10) was significantly greater (3.88 +/- 1.19 vs. 2.51 +/- 1.08 muscle lengths/s, P < 0.05). These results provide evidence that myosin light chain 2 regulates cross-bridge cycling rate. The faster rate of cycling in the presence of MLC2v suggests that the MLC2v isoform may contribute to the greater power-generating capabilities of the ventricle compared with the atrium.
Animals↗
Aging-dependent depression in the kinetics of force development in rat skinned myocardium.
Normal aging of the rodent heart results in prominent prolongation of the twitch. We tested the hypothesis that increased expression of beta-myosin heavy chain (MHC), as occurs in the normal aging process in the rodent heart, contributes to the prolongation of the twitch by depressing the kinetics of cross-bridge interaction. Using 3-, 9-, 21-, and 33-mo-old male Fischer 344 x Brown Norway F1 hybrid rats, we examined both the rate of tension development (kCa) and unloaded shortening velocity in chemically skinned myocardium. Although kCa in all four age groups was dependent on the level of Ca2+ activation, both submaximal and maximal kCa were significantly slower in 9-, 21-, and 33-mo-old rats relative to 3-mo-old rats. Furthermore, unloaded shortening velocity was significantly reduced in 9-, 21-, and 33-mo-old rats compared with 3-mo-old rats. Collectively, these data strongly suggest that the aging-related increase in beta-MHC expression results in a progressive slowing of cross-bridge interaction kinetics in skinned myocardium, which most likely contributes to the overall aging-dependent reduction in myocardial functional capacity.
Acetates↗
Cardiac myosin heavy chains lacking the light chain binding domain cause hypertrophic cardiomyopathy in mice.
Myosin is a chemomechanical motor that converts chemical energy into the mechanical work of muscle contraction. More than 40 missense mutations in the cardiac myosin heavy chain (MHC) gene and several mutations in the two myosin light chains cause a dominantly inherited heart disease called familial hypertrophic cardiomyopathy. Very little is known about the biochemical defects in these alleles and how the mutations lead to disease. Because removal of the light chain binding domain in the lever arm of MHC should alter myosin's force transmission but not its catalytic function, we tested the hypothesis that such a mutant MHC would act as a dominant mutation in cardiac muscle. Hearts from transgenic mice expressing this mutant myosin are asymmetrically hypertrophied, with increases in mass primarily restricted to the cardiac anterior wall. Histological examination demonstrates marked cellular hypertrophy, myocyte disorganization, small vessel coronary disease, and severe valvular pathology that included thickening and plaque formation. Skinned myocytes and multicellular preparations from transgenic hearts exhibited decreased Ca2+ sensitivity of tension and decreased relaxation rates after flash photolysis of diazo 2. These experiments demonstrate that alterations in myosin force transmission are sufficient to trigger the development of hypertrophic cardiomyopathy.
Animals↗
Methionine infusion reproduces liver injury of parenteral nutrition cholestasis.
Cholestatic jaundice is the major complication of total parenteral nutrition (TPN) in infancy. We have previously shown that the TPN solution is directly toxic to the liver, and that this toxicity appears to be mediated by one or more amino acids. Elevated serum methionine levels, without corresponding increases in its metabolites, suggest that accumulation of this toxic amino acid may cause TPN cholestasis. Nine-week-old rabbits (n = 28) were divided into three groups. The FED group was fed standard rabbit chow ad libitum. The TPN group was not fed and received only i.v. TPN (including methionine 121 mg.kg-1.d-1), and lipids. The EXP group was fed chow ad libitum and received i.v. methionine (121 mg.kg-1.d-1). After 14 d, we evaluated bile flow, bromosulfophthalein excretion, serum liver enzymes, liver histology, and serum amino acid levels. Bile flow was significantly depressed in the TPN and EXP groups compared with FED controls (32.9 +/- 9.4 and 45.7 +/- 14.4 versus 82.9 +/- 13.8). Excretion of the bilirubin analog bromosulfophthalein tended to be delayed by methionine infusion (p = 0.15). Serum liver enzymes (aspartate transaminase, alanine aminotransferase, gamma-glutamyltransferase, and alkaline phosphatase) were normal in all groups. Histologic liver injury in the EXP group was similar to that caused by TPN. Balloon degeneration, and portal inflammation were seen in both groups. Homocysteine, an early metabolite of methionine, was elevated in the TPN and EXP groups compared with FED controls. Intravenous methionine is hepatotoxic. Despite full oral feeding, it produces a depression of bile flow and histologic liver injury similar to that seen with TPN. Elevated homocysteine levels suggests an enzymatic block early in the pathway of methionine metabolism. We believe that methionine may be an important factor in the pathogenesis of TPN cholestasis.
Amino Acids↗
Rapid action of 17beta-estradiol on kainate-induced currents in hippocampal neurons lacking intracellular estrogen receptors.
17Beta-estradiol can potentiate kainate-induced currents in isolated hippocampal CA1 neurons. The action of estrogen was rapid in onset, steroid and stereospecific, and reversible. The potentiation could be mimicked by 8-bromo-cAMP, an activator of protein kinase A. As the hippocampus expresses both isoforms of the intracellular estrogen receptor (ER alpha and ER beta), the role of ERs in the rapid action of 17beta-estradiol remains elusive. Here we report that the rapid action of 17beta-estradiol is independent from the classical ER activation in the modulation of membrane excitability. Under whole cell voltage clamp recording configuration, 17beta-estradiol-induced potentiation was observed in both wild-type and the ER alpha gene knockout mice. The perfusion or incubation of ICI 182,780, which blocks both ER alpha and ER beta, did not affect estrogen potentiation in either group. Further study showed that adenosine 3',5'-cyclic-monophosphothioate Rp-isomer, a specific inhibitor of protein kinase A, completely blocked the potentiation observed with the application of 17beta-estradiol in ER alpha gene knockout mice. Our results provide evidence that a distinct estrogen-binding site exists, which appears to be coupled to alpha-amino-3-hydroxyl-5-methyl-4-isoxazole proprionic acid/kainate receptors by a cAMP-dependent phosphorylation process.
Animals↗
Role of myosin heavy chain composition in kinetics of force development and relaxation in rat myocardium.
1. The effects of ventricular myosin heavy chain (MHC) composition on the kinetics of activation and relaxation were examined in both chemically skinned and intact myocardial preparations from adult rats. Thyroid deficiency was induced to alter ventricular MHC isoform expression from approximately 80% alpha-MHC/20% beta-MHC in euthyroid rats to 100% beta-MHC, without altering the expression of thin-filament-associated regulatory proteins. 2. In single skinned myocytes, increased expression of beta-MHC did not significantly affect either maximal Ca2+-activated tension (P0) or the Ca2+ sensitivity of tension (pCa50). However, unloaded shortening velocity (V0) decreased by 80% due to increased beta-MHC expression. 3. The kinetics of activation and relaxation were examined in skinned multicellular preparations using the caged Ca2+ compound DM-nitrophen and caged Ca2+ chelator diazo-2, respectively. Myocardium expressing 100% beta-MHC exhibited apparent rates of submaximal and maximal tension development (kCa) that were 60% lower than in control myocardium, and a 2-fold increase in the half-time for relaxation from steady-state submaximal force. 4. The time courses of cell shortening and intracellular Ca2+ transients were assessed in living, electrically paced myocytes, both with and without beta-adrenergic stimulation (70 nM isoproterenol (isoprenaline)). Thyroid deficiency had no affect on either the extent of myocyte shortening or the resting or peak fura-2 fluorescence ratios. However, induction of beta-MHC expression by thyroid deficiency was associated with increased half-times for myocyte shortening and relengthening and increased half-time for the decay of the fura-2 fluorescence ratio. Qualitatively similar results were obtained in both the absence and the presence of beta-adrenergic stimulation although the beta-agonist accelerated the kinetics of the twitch and the Ca2+ transient. 5. Collectively, these data provide evidence that increased beta-MHC expression contributes significantly to the observed depression of contractile function in thyroid deficient myocardium by slowing the rates of both force development and force relaxation.
Adrenergic beta-Agonists↗
Strong binding of myosin modulates length-dependent Ca2+ activation of rat ventricular myocytes.
Reductions in sarcomere length (SL) and concomitant increases in interfilament lattice spacing have been shown to decrease the Ca2+ sensitivity of tension in myocardium. We tested the idea that increased lattice spacing influences the SL dependence of isometric tension by reducing the probability of strong interactions of myosin crossbridges with actin, thereby decreasing cooperative activation of the thin filament. Single ventricular myocytes were isolated by enzymatic digestion of rat hearts and were subsequently rapidly skinned. Maximal tension and Ca2+ sensitivity of tension (ie, pCa50) were measured in the absence and presence of N-ethylmaleimide-modified myosin subfragment 1 (NEM-S1) at both short and long SLs. NEM-S1, a strong-binding non-tension-generating derivative of the myosin head, was applied to single skinned myocytes to cooperatively promote strong binding of endogenous myosin crossbridges. Compared with control myocytes at SL of approximately 1.90 microm, application of NEM-S1 markedly increased submaximal Ca2+-activated tensions and thereby increased Ca2+ sensitivity; ie, pCa50 increased from 5.40+/-0.02 to 5.52+/-0.02 pCa units in the presence of NEM-S1. Furthermore, NEM-S1 treatment reversibly eliminated the SL dependence of the Ca2+ sensitivity of tension, in that the DeltapCa50 between short and long lengths was 0. 02+/-0.01 pCa units in the presence of NEM-S1 compared with a DeltapCa50 of 0.10+/-0.01 pCa units in control myocytes. From these results we conclude that the decrease in the Ca2+ sensitivity of tension at short SL results predominantly from decreased cooperative activation of the thin filament due to reductions in the number of strong-binding crossbridges.
Animals↗
Force-velocity and power-load curves in rat skinned cardiac myocytes.
1. This study utilized a skinned myocyte preparation with low end compliance to examine force-velocity and power-load curves at 12 C in myocytes from rat hearts. 2. In maximally activated myocyte preparations, shortening velocities appeared to remain constant during load clamps in which shortening took place over a sarcomere length range of approximately 2.30-2.00 micro m. These results suggest that previously reported curvilinear length traces during load clamps of multicellular preparations were due in part to extracellular viscoelastic structures that give rise to restoring forces during myocardial shortening. 3. During submaximal Ca2+ activations, the velocity of shortening at low loads slowed and the time course of shortening became curvilinear, i.e. velocity progressively slowed as shortening continued. This result implies that cross-bridge cycling kinetics are slower at low levels of activation and that an internal load arises during shortening of submaximally activated myocytes, perhaps due to slowly detaching cross-bridges. 4. Reduced levels of activator Ca2+ also reduced maximal power output and increased the relative load at which power output was optimal. For a given absolute load, the shift has the effect of maintaining power output near the optimum level despite reductions in cross-bridge number and force generating capability at lower levels of Ca2+.
Animals↗
Novel mechanism for non-genomic action of 17 beta-oestradiol on kainate-induced currents in isolated rat CA1 hippocampal neurones.
1. Using whole-cell voltage-clamp recordings of dissociated hippocampal CA1 neurones, we demonstrated that 17 beta-oestradiol rapidly potentiates kainate-induced currents when applied either to the outside or the inside of the neurone. However, when the steroid was conjugated to bovine serum albumin (E2-BSA), application to either the extracellular plasma membrane (E2-BSAout) or the cytosolic side of the cell (E2-BSAin) had no observable effect on kainate-induced currents. However, when applied stimultaneously to both sides of the plasma membrane, E2-BSA potentiated kainate-induced currents. 2. Application of E2-BSAout and GTP gamma S(in) potentiated kainate-induced currents. The potentiation of kainate-induced currents by 17 beta-oestradiol was occluded by cholera toxin pretreatment and appeared to be pertussis toxin insensitive. 3. E2-BSAin prolonged the effect of 8-bromoadenosine 3',5' cyclic monophosphate (8-bromo-cAMP) on kainate-induced currents. The recovery from the 8-bromo-cAMP response was found to be a function of the concentration of E2-BSAin. The application of ATP gamma S(in) occluded the effect of 17 beta-oestradiol. 4. These results suggest that the non-genomic action of 17 beta-oestradiol in the potentiation of kainate-induced currents is mediated via an action on Gs protein-coupled receptors. This operates in concert with an internal action of 17 beta-oestradiol on a cAMP-dependent phosphorylation.
Animals↗
Incorporation of the troponin regulatory complex of post-ischemic stunned porcine myocardium reduces myofilament calcium sensitivity in rabbit psoas skeletal muscle fibers.
Decreased calcium sensitivity of tension in post-ischemic myocardium is thought to be a mechanism of depressed function in stunning. The purpose of this study was to determine if the decrease in calcium sensitivity of tension results from ischemia and/or reperfusion-induced alterations in the thin filament regulatory troponin. The experiments utilized an open-chest porcine model of regional LAD myocardial stunning that has previously been shown to cause a decrease in calcium sensitivity of tension in permeabilized myocytes. Stunning was induced by 45 min of low-flow ischemia to the left anterior descending (LAD) coronary artery perfusion bed, which was followed by 30 min of reperfusion. Regional LAD function after reperfusion was 0.5+/-2.8%, as assessed by systolic wall thickening (v 23.9+/-4.1% thickening in control, P<0.001). Core biopsy samples from control circumflex and stunned LAD myocardium were acquired from each heart (n=9) after LAD reperfusion, and were used to obtain purified troponin complexes. Isometric tension-pCa relationships were measured in permeabilized psoas skeletal fibers before and after partial exchange of cardiac troponin from either control circumflex (n=6) or stunned LAD (n=8) myocardium for endogenous skeletal troponin. Calcium sensitivity of tension as assessed by pCa50 (i.e. pCa for half-maximal tension) was unchanged after exchange of troponin from control circumflex myocardium (pCa50=5. 98+/-0.02 v 5.96+/-0.06), but there was a significant decrease in calcium sensitivity of tension after exchange of troponin from stunned LAD myocardium (pCa50=5.97+/-0.07 v 5.82+/-0.05, P<0.05). We conclude that the decrease in calcium sensitivity of tension in postischemic stunned myocardium is, in part, due to ischemia and/or reperfusion-induced alterations in the cardiac troponin regulatory complex.
Actin Cytoskeleton↗
Progressive pan-colonic fibrosis secondary to oral administration of pancreatic enzymes.
Most patients with cystic fibrosis require oral administration of pancreatic enzymes to treat pancreatic insufficiency. Recent use of higher-strength enzyme preparations in large doses has been found to be associated with fibrotic strictures of the colon. We report a case of pancolonic fibrosis due to pancreatic enzyme use.
Child↗
Phosphorylation of myosin regulatory light chain eliminates force-dependent changes in relaxation rates in skeletal muscle.
The rate of relaxation from steady-state force in rabbit psoas fiber bundles was examined before and after phosphorylation of myosin regulatory light chain (RLC). Relaxation was initiated using diazo-2, a photolabile Ca2+ chelator that has low Ca2+ binding affinity (K(Ca) = 4.5 x 10(5) M(-1)) before photolysis and high affinity (K(Ca) = 1.3 x 10(7) M(-1)) after photolysis. Before phosphorylating RLC, the half-times for relaxation initiated from 0.27 +/- 0.02, 0.51 +/- 0.03, and 0.61 +/- 0.03 Po were 90 +/- 6, 140 +/- 6, and 182 +/- 9 ms, respectively. After phosphorylation of RLC, the half-times for relaxation from 0.36 +/- 0.03 Po, 0.59 +/- 0.03 Po, and 0.65 +/- 0.02 Po were 197 +/- 35 ms, 184 +/- 35 ms, and 179 +/- 22 ms. This slowing of relaxation rates from steady-state forces less than 0.50 Po was also observed when bundles of fibers were bathed with N-ethylmaleimide-modified myosin S-1, a strongly binding cross-bridge derivative of S1. These results suggest that phosphorylation of RLC slows relaxation, most likely by slowing the apparent rate of transition of cross-bridges from strongly bound (force-generating) to weakly bound (non-force-generating) states, and reduces or eliminates Ca2+ and cross-bridge activation-dependent changes in relaxation rates.
Animals↗
The failed anoplasty: successful outcome after reoperative anoplasty and sigmoid resection.
BACKGROUND/PURPOSE: Children with anorectal malformations often have less than optimal results after repair. The authors report on five patients (ages 3 to 17 years) born with imperforate anus and treated with anoplasty as a newborn. At presentation, all patients were completely incontinent of stool. None had ever experienced voluntary bowel movements, and all wore diapers continuously. METHODS: Perineal examination with the nerve stimulator showed the muscle complex was largely intact with good contraction, but the neoanus was outside of the muscle complex. Contrast enema showed massive dilation of the rectosigmoid colon and fecal impaction. A tethered spinal cord was excluded by magnetic resonance imaging (MRI). We treated these patients with a combined reoperative anoplasty via the posterior sagittal approach and sigmoid resection. RESULTS: Within 6 months after the procedure, all patients had achieved complete continence. They had from one to three voluntary bowel movements per day without soiling. CONCLUSIONS: Children with severe constipation and fecal incontinence after anoplasty should undergo evaluation by a surgeon. If examination shows a reasonably intact muscle complex and correctable anatomic defects, an excellent result can be achieved with appropriate reoperation.
Adolescent↗