Predictive Abilities of the Frailty Phenotype and the Swiss Frailty Network and Repository Frailty Index for Non-Home Discharge and Functional Decline in Hospitalized Geriatric Patients.

BACKGROUND: Frailty is increasingly applied as a measure to predict clinical outcomes, but data on the predictive abilities of frailty measures for non-home discharge and functional decline in acutely hospitalized geriatric patients are scarce. OBJECTIVES: The aim of this study was to investigate the predictive ability of the frailty phenotype and a frailty index currently validated as part of the ongoing Swiss Frailty Network and Repository Study based on clinical admission data for non-home discharge and functional decline in acutely hospitalized older patients. DESIGN: Prospective cohort study. SETTING AND PARTICIPANTS: Data were analyzed from 334 consecutive hospitalized patients of a tertiary acute care geriatric inpatient clinic admitted between August 2020 and March 2021. MEASUREMENTS: We assessed frailty using 1) the frailty phenotype and 2) the Swiss Frailty Network and Repository Study (SFNR) frailty index based on routinely available clinical admission data. Predictive abilities of both frailty measures were analyzed for the clinical outcomes of non-home discharge and functional decline using multivariate logistic regression models and receiver operating characteristic curves (ROC). RESULTS: Mean age was 82.8 (SD 7.2) years and 55.4% were women. Overall, 170 (53.1%) were frail based on the frailty phenotype and 220 (65.9%) based on the frailty index. Frail patients based on the frailty phenotype were more likely to be discharged non-home (55 (32.4%) vs. 26 (17.3%); adjusted OR 2.4 (95% CI, 1.4, 5.1)). Similarly, frail patients based on the frailty index were more likely to be discharged non-home compared to non-frail patients (76 (34.6%) vs. 9 (7.9%); adjusted OR, 5.5 (95% CI, 2.6, 11.5)). Both, the frailty phenotype and the frailty index were similarly associated with functional decline (adjusted OR 2.7 (95% CI, 1.5, 4.9); adjusted OR 2.8 (95% CI 1.4, 5.5)). ROC analyses showed best discriminatory accuracy for the frailty index for non-home discharge (area under the curve 0.76). CONCLUSIONS: Frailty using the SFNR-frailty index and the frailty phenotype is a promising measure for prediction of non-home discharge and functional decline in acutely hospitalized geriatric patients. Further study is needed to define the most valid frailty measure.

Patterns of Limb and Epaxial Muscle Activity During Walking in the Fire Salamander, Salamandra salamandra.

Salamanders and newts (urodeles) are often used as a model system to elucidate the evolution of tetrapod locomotion. Studies range from detailed descriptions of musculoskeletal anatomy and segment kinematics, to bone loading mechanics and inferring central pattern generators. A further area of interest has been in vivo muscle activity patterns, measured through electromyography (EMG). However, most prior EMG work has primarily focused on muscles of the forelimb or hindlimb in specific species or the axial system in others. Here we present data on forelimb, hindlimb, and epaxial muscle activity patterns in one species, Salamandra salamandra, during steady state walking. The data are calibrated to limb stride cycle events (stance phase, swing phase), allowing direct comparisons to homologous muscle activation patterns recorded for other walking tetrapods (e.g., lizards, alligators, turtles, mammals). Results demonstrate that Salamandra has similar walking kinematics and muscle activity patterns to other urodele species, but that interspecies variation does exist. In the forelimb, both the m. dorsalis scapulae and m. latissimus dorsi are active for 80% of the forelimb swing phase, while the m. anconaeus humeralis lateralis is active at the swing-stance phase transition and continues through 86% of the stance phase. In the hindlimb, both the m. puboischiofemoralis internus and m. extensor iliotibialis anterior are active for 30% of the hindlimb swing phase, while the m. caudofemoralis is active 65% through the swing phase and remains active for most of the stance phase. With respect to the axial system, both the anterior and posterior m. dorsalis trunci display two activation bursts, a pattern consistent with stabilization and rotation of the pectoral and pelvic girdles. In support of previous assertions, comparison of Salamandra muscle activity timings to other walking tetrapods revealed broad-scale similarities, potentially indicating conservation of some aspects of neuromuscular function across tetrapods. Our data provide the foundation for building and testing dynamic simulations of fire salamander locomotor biomechanics to better understand musculoskeletal function. They could also be applied to future musculoskeletal simulations of extinct species to explore the evolution of tetrapod locomotion across deep-time.

Padrones de actividad muscular epaxial y apendicular durante la cursorialidad de la salamandra-de-fuego, Salamandra salamandra Las salamandras y los tritones (urodelos) son utilizados con frecuencia como un sistema modelo para dilucidar la evolución de la locomoción en los tetrápodos. Los estudios previos varían de descripciones detalladas de la anatomía musculoesquelética y cinemática de los segmentos del cuerpo, a la mecánica de la capacidad de soporte de carga estructural ósea y la generación de padrones centrales. Otra área de interés ha sido los padrones de actividad muscular in vivo, medidos por electromiografía (EMG). Sin embargo, la mayoría de los trabajos anteriores con EMG se han centrado principalmente en los músculos de los miembros anteriores o posteriores en especies específicas o en el sistema axial de otras. En este trabajo, presentamos datos sobre los padrones de actividad muscular en los músculos de los miembros anteriores, posteriores y de la musculatura epaxial en una especie, Salamandra salamandra, durante la marcha continua. Los datos se calibran para los períodos del ciclo de caminar de los miembros (fase de soporte, fase de movimiento), lo que permite comparaciones directas con padrones de activación muscular homólogos registrados para otros tetrápodos cursoriales (por ejemplo, lagartos, caimanes, tortugas y mamíferos). Los resultados demuestran que Salamandra tiene padrones de cinemática cursorial y actividad muscular similares a otras especies de urodelos, pero con variación interespecífica. En los miembros anteriores, ambos los m. dorsalis scapulae y m. latissimus dorsi están activos en 80% de la fase de movimiento del miembro anterior, mientras que el m. anconaeus humeralis lateralis se activa en la transición de la fase de movimiento-soporte y permanece activo en 86% de la fase de soporte. En los miembros posteriores, ambos m. puboischiofemoralis internus y m. extensor iliotibialis anterior están activos en 30% de la fase de movimiento de los miembros posteriores, mientras que el m. caudofemoralis está activo durante el 65% de la fase de movimiento, permaneciendo activo durante la mayor parte de la fase de soporte. Con respecto al sistema axial, las porciones anterior y posterior del m. dorsalis trunci exhibe dos períodos de activación, un padrón consistente con la estabilización y rotación de la cintura pélvica y pectoral. Como sugirido anteriormente, la comparación de los tiempos de actividad muscular de Salamandra con otros tetrápodos cursoriales reveló similitudes en gran escala, lo que podría indicar la conservación de algunos aspectos de la función neuromuscular entre los tetrápodos. Nuestros datos proporcionan una base para la construcción y prueba de simulaciones dinámicas de la biomecánica locomotora de salamandras-de-fuego para comprender mejor las funciones musculoesqueléticas. Nuestros resultados también se pueden aplicar a futuras simulaciones musculoesqueléticas de especies extintas para explorar la evolución de la locomoción de tetrápodos en el tiempo profundo.

Padrões de atividade muscular epaxial e apendicular durante a cursorialidade da salamandra-de-fogo, Salamandra salamandra Salamandras e tritões (urodelos) são freqüentemente utilizados como um sistema modelo para elucidar a evolução da locomoção em tetrápodes. Estudos anteriores variam de descrições detalhadas da anatomia musculoesquelética e cinemática dos segmentos corporais, a mecânica da capacidade de carga estrutural óssea e geradora de padrões centrais. Uma outra área de interesse tem sido os padrões de atividade muscular in vivo, medidos por eletromiografia (EMG). No entanto, a maioria dos trabalhos anteriores de EMG concentrou-se principalmente nos músculos dos membros anteriores ou posteriores em espécies específicas ou no sistema axial de outras. Nesse trabalho, apresentamos dados sobre os padrões de atividade muscular nos membros anteriores, posteriores e musculatura epaxial em uma espécie, Salamandra salamandra, durante caminhada em modo contínuo. Os dados são calibrados para os períodos do ciclo de caminhada dos membros (fase de apoio, fase de movimento), permitindo comparações diretas com padrões de ativação muscular homólogos registrados para outros tetrápodes cursoriais (por exemplo, lagartos, jacarés, tartarugas e mamíferos). Os resultados demonstram que Salamandra possui padrões de cinemática cursorial e atividade muscular semelhantes à outras espécies de urodelos, mas com variação interespecífica. Nos membros anteriores, ambos os m. dorsalis scapulae e m. latissimus dorsi estão ativos em 80% da fase de movimento do membro anterior, enquanto o m. anconaeus humeralis lateralis é ativado na transição da fase de movimento-apoio e continua ativo em 86% da fase de apoio. Nos membros posteriores, ambos m. puboischiofemoralis internus e m. extensor iliotibialis anterior estão ativos em 30% da fase de movimento dos membros posteriores, enquanto o m. caudofemoralis está ativo por 65% da fase de movimento, permanecendo ativo na maior parte da fase de apoio. No que diz respeito ao sistema axial, as porções anterior e posterior do m. dorsalis trunci exibe dois períodos de ativação, um padrão consistente com a estabilização e rotação da cintura peitoral e pélvica. Como préviamente sugerido, a comparação dos tempos de atividade muscular de Salamandra com outros tetrápodes cursoriais revelou similaridades em larga escala, potencialmente indicando a conservação de alguns aspectos da função neuromuscular entre tetrápodes. Os nossos dados fornecem uma base para a construção e testagem de simulações dinâmicas da biomecânica locomotora de salamandras-de-fogo para se entender melhor as funções músculo-esqueléticas. Nossos resultados também podem ser aplicados a futuras simulações músculo-esqueléticas de espécies extintas para explorar a evolução da locomoção de tetrápodes no tempo profundo.

Three-dimensional movements of the pelvis and the lumbar intervertebral joints in walking and trotting dogs.

Current knowledge of the physiological range of motion (ROM) in the canine axial system during locomotion is relatively limited. This is particularly problematic because dogs with back-related dysfunction frequently present for routine consultations. To collect detailed kinematic information and describe the three-dimensional motions of the pelvis and the lumbar spine (i.e. intervertebral joints S1/L7-L2/L1), we recorded ventro-dorsal and latero-lateral X-ray videos of three walking and trotting dogs and reconstructed their pelvic and intervertebral motions using X-ray reconstruction of moving morphology and scientific rotoscoping. Pelvic roll displayed a monophasic motion pattern and the largest ROM with on average 13° and 11° during walking and trotting, respectively. Pelvic yaw had the smallest ROM with on average 5° (walk) and 6° (trot). A biphasic pattern was observed for pelvic pitch with a mean ROM of 8°. At both gaits, the greatest intervertebral motions occurred either in S1/L7 or L7/L6. The intervertebral motions were mono- or biphasic in the horizontal and the transverse body planes and biphasic in the sagittal plane. Cranial to L6/5, the ROM tended to decrease from 3° to <1.5° in all three planes. Our results confirm that pelvic displacement and intervertebral joint movements are tightly linked with pelvic limb action at symmetrical gaits. The overall small movements, particularly cranial to L5, are consistent with the epaxial musculature globally stabilising the spine against the external and internal limb forces acting on the pelvis and the trunk during walking and trotting.

Kinematic adaptations to tripedal locomotion in dogs.

Limb amputation often represents the only treatment option for canine patients with certain diseases or injuries of the appendicular system. Previous studies have investigated adaptations to tripedal locomotion in dogs but there is a lack of understanding of biomechanical compensatory mechanisms. This study evaluated the kinematic differences between quadrupedal and tripedal locomotion in nine healthy dogs running on a treadmill. The loss of the right pelvic limb was simulated using an Ehmer sling. Kinematic gait analysis included spatio-temporal comparisons of limb, joint and segment angles of the remaining pelvic and both thoracic limbs. The following key parameters were compared between quadrupedal and tripedal conditions: angles at touch-down and lift-off, minimum and maximum joint angles, plus range of motion. Significant differences in angular excursion were identified in several joints of each limb during both stance and swing phases. The most pronounced differences concerned the remaining pelvic limb, followed by the contralateral thoracic limb and, to a lesser degree, the ipsilateral thoracic limb. The thoracic limbs were, in general, more retracted, consistent with pelvic limb unloading and previous observations of bodyweight re-distribution in amputees. Proximal limb segments showed more distinct changes than distal ones. Particularly, the persistently greater anteversion of the pelvis probably affects the axial system. Overall, tripedal locomotion requires concerted kinematic adjustments of both the appendicular and axial systems, and consequently preventive, therapeutic and rehabilitative care of canine amputees should involve the whole musculoskeletal apparatus.

Ground reaction force adaptations to tripedal locomotion in dogs.

To gain insight into the adaptive mechanisms to tripedal locomotion and increase understanding of the biomechanical consequences of limb amputation, this study investigated kinetic and temporal gait parameters in dogs before and after the loss of a hindlimb was simulated. Nine clinically sound Beagle dogs trotted on an instrumented treadmill and the ground reaction forces as well as the footfall patterns were compared between quadrupedal and tripedal locomotion. Stride and stance durations decreased significantly in all limbs when the dogs ambulated tripedally, while relative stance duration increased. Both vertical and craniocaudal forces were significantly different in the remaining hindlimb. In the forelimbs, propulsive force increased in the contralateral and decreased in the ipsilateral limb, while the vertical forces were unchanged (except for mean force in the contralateral limb). Bodyweight was shifted to the contralateral and cranial body side so that each limb bore ~33% of the dog's bodyweight. The observed changes in the craniocaudal forces and the vertical impulse ratio between the fore- and hindlimbs suggest that a nose-up pitching moment occurs during the affected limb pair's functional step. To regain pitch balance for a given stride cycle, a nose-down pitching moment is exerted when the intact limb pair supports the body. These kinetic changes indicate a compensatory mechanism in which the unaffected diagonal limb pair is involved. Therefore, the intact support pair of limbs should be monitored closely in canine hindlimb amputees.

Fibre type composition in the lumbar perivertebral muscles of primates: implications for the evolution of orthogrady in hominoids.

The axial musculoskeletal system is important for the static and dynamic control of the body during both locomotor and non-locomotor behaviour. As a consequence, major evolutionary changes in the positional habits of a species are reflected by morpho-functional adaptations of the axial system. Because of the remarkable phenotypic plasticity of muscle tissue, a close relationship exists between muscle morphology and function. One way to explore major evolutionary transitions in muscle function is therefore by comparative analysis of fibre type composition. In this study, the three-dimensional distribution of slow and fast muscle fibres was analysed in the lumbar perivertebral muscles of two lemuriform (mouse lemur, brown lemur) and four hominoid primate species (white-handed gibbon, orangutan, bonobo, chimpanzee) in order to develop a plausible scenario for the evolution of the contractile properties of the axial muscles in hominoids and to discern possible changes in muscle physiology that were associated with the evolution of orthogrady. Similar to all previously studied quadrupedal mammals, the lemuriform primates in this study exhibited a morpho-functional dichotomy between deep slow contracting local stabilizer muscles and superficial fast contracting global mobilizers and stabilizers and thus retained the fibre distribution pattern typical for quadrupedal non-primates. In contrast, the hominoid primates showed no regionalization of the fibre types, similar to previous observations in Homo. We suggest that this homogeneous fibre composition is associated with the high functional versatility of the axial musculature that was brought about by the evolution of orthograde behaviours and reflects the broad range of mechanical demands acting on the trunk in orthograde hominoids. Because orthogrady is a derived character of euhominoids, the uniform fibre type distribution is hypothesized to coincide with the evolution of orthograde behaviours.

Compensatory load redistribution in walking and trotting dogs with hind limb lameness.

This study evaluated adaptations in vertical force and temporal gait parameters to hind limb lameness in walking and trotting dogs. Eight clinically normal adult Beagles were allowed to ambulate on an instrumented treadmill at their preferred speed while the ground reaction forces were recorded for all limbs before and after a moderate, reversible, hind limb lameness was induced. At both gaits, vertical force was decreased in the ipsilateral and increased in the contralateral hind limb. While peak force increased in the ipsilateral forelimb, no changes were observed for mean force and impulse when the dogs walked or trotted. In the contralateral forelimb, the peak force was unchanged, but the mean force significantly increased during walking and trotting; vertical impulse increased only during walking. Relative stance duration increased in the ipsilateral hind limb when the dogs trotted. In the contralateral fore and hind limbs, relative stance duration increased during walking and trotting, but decreased in the ipsilateral forelimb during walking. Analysis of load redistribution and temporal gait changes during hind limb lameness showed that compensatory mechanisms were similar regardless of gait. The centre of mass consistently shifted to the contralateral body side and cranio-caudally to the side opposite the affected limb. These biomechanical changes indicate substantial short- and long-term effects of hind limb lameness on the musculoskeletal system.

The hedgehog processing pathway is required for NSCLC growth and survival.

Considerable interest has been generated from the results of recent clinical trials using smoothened (SMO) antagonists to inhibit the growth of hedgehog (HH) signaling-dependent tumors. This interest is tempered by the discovery of SMO mutations mediating resistance, underscoring the rationale for developing therapeutic strategies that interrupt HH signaling at levels distinct from those inhibiting SMO function. Here, we demonstrate that HH-dependent non-small cell lung carcinoma (NSCLC) growth is sensitive to blockade of the HH pathway upstream of SMO, at the level of HH ligand processing. Individually, the use of different lentivirally delivered shRNA constructs targeting two functionally distinct HH-processing proteins, skinny hedgehog (SKN) or dispatched-1 (DISP-1), in NSCLC cell lines produced similar decreases in cell proliferation and increased cell death. Further, providing either an exogenous source of processed HH or a SMO agonist reverses these effects. The attenuation of HH processing, by knocking down either of these gene products, also abrogated tumor growth in mouse xenografts. Finally, we extended these findings to primary clinical specimens, showing that SKN is frequently overexpressed in NSCLC and that higher DISP-1 expression is associated with an unfavorable clinical outcome. Our results show a critical role for HH processing in HH-dependent tumors, identifies two potential druggable targets in the HH pathway, and suggest that similar therapeutic strategies could be explored to treat patients harboring HH ligand-dependent cancers.

The influence of foot posture on the cost of transport in humans.

Although humans appear to be specialized for endurance running, the plantigrade posture of our feet, in which the heel contacts the substrate at the beginning of a step, seems incompatible with economical running. In this study, we tested the hypothesis that plantigrade foot posture reduces the energetic cost of transport (COT) during walking in humans. When human subjects walked with their heels slightly elevated in a 'low-digitigrade' posture, COT increased by 53% above that of normal plantigrade walking. By contrast, there was no difference in COT when subjects ran with digitigrade versus plantigrade foot posture. Stride frequency increased and stride length decreased when subjects switched to digitigrade walking; however, this change did not influence the COT. Additionally, we found that possible reductions in postural stability appear not to have caused the elevated cost of digitigrade walking. Digitigrade walking, however, did (1) increase the external mechanical work performed by the limbs; (2) reduce the pendular exchange of kinetic and potential energy of the center of mass; (3) increase the average ground reaction force moment at the ankle joint; and (4) increase the recruitment of major extensor muscles of the ankle, knee, hip and back. These observations suggest that plantigrade foot posture improves the economy of walking. Relative to other mammals, humans are economical walkers, but not economical runners. Given the great distances hunter-gatherers travel, it is not surprising that humans retained a foot posture, inherited from our more arboreal great ape ancestors, that facilitates economical walking.

Inbreeding avoidance in spiders: evidence for rescue effect in fecundity of female spiders with outbreeding opportunity.

Selection by inbreeding depression should favour mating biases that reduce the risk of fertilization by related mates. However, equivocal evidence for inbreeding avoidance questions the strength of inbreeding depression as a selective force in the evolution of mating biases. Lack of inbreeding avoidance can be because of low risk of inbreeding, variation in tolerance to inbreeding or high costs of outbreeding. We examined the relationship between inbreeding depression and inbreeding avoidance adaptations under two levels of inbreeding in the spider Oedothorax apicatus, asking whether preference for unrelated sperm via pre- and/or post-copulatory mechanisms could restore female fitness when inbreeding depression increases. Using inbred isofemale lines we provided female spiders with one or two male spiders of different relatedness in five combinations: one male sib; one male nonsib; two male sibs; two male nonsibs; one male sib and one male nonsib. We assessed the effect of mating treatment on fecundity and hatching success of eggs after one and three generations of inbreeding. Inbreeding depression in F1 was not sufficient to detect inbreeding avoidance. In F3, inbreeding depression caused a major decline in fecundity and hatching rates of eggs. This effect was mitigated by complete recovery in fecundity in the sib-nonsib treatment, whereas no rescue effect was detected in the hatching success of eggs. The rescue effect is best explained by post-mating discrimination against kin via differential allocation of resources. The natural history of O. apicatus suggests that the costs of outbreeding may be low which combined with high costs of inbreeding should select for avoidance mechanisms. Direct benefits of post-mating inbreeding avoidance and possibly low costs of female multiple mating can favour polyandry as an inbreeding avoidance mechanism.

Musculoskeletal support of lumbar spine stability.

Using a biomechanical model and experimental data the self-stabilising behaviour of antagonistic trunk muscles was analyzed. The biomechanical model is constituted of a pair of antagonistic Hill-type muscles, their geometric arrangement with respect to the spine, and the instantaneous centre of rotation in frontal plane. Using Ljapunov's theory, the stability of certain motion and loading situations was analyzed. Applying a sensitivity analysis, the influence of different muscle properties and the geometric arrangement on stability was investigated. The simulations revealed that the stability of spinal movements depended primarily on the geometrical arrangement of muscles and the position of the centre of rotation of the spine, the latter was affected in turn by the activities of the profound muscles. To stabilize the situations simulated oblique muscle arrangements were necessary. In order to define an instantaneous centre of rotation in the lower region of the spine negative attachment angles (medio-lateral decline) of muscles were necessary, corresponding to the real anatomy of obliquus externus muscles. More cranially located instantaneous centres of rotation required positive attachment angles for stability, corresponding to obliquus internus or multifidus muscles. Furthermore, the fibre-type distribution of muscles influenced the stability of the system, i.e. a high percentage of fast-twitch-fibres supported the stabilisation. Conclusions drawn from the simulations were supported by experimental data. Sudden loads and quick-release perturbations with two different amplitudes were applied to the upper body of ten male subjects. In comparison to sudden load situations preactivation of muscles due to an external load, i.e. quick-release perturbation, led to significantly less dependency of the amplitude of deflection on the amplitude of the perturbation. This observation relates to the self-stabilising properties of the musculoskeletal system. In conclusion, training seems to be advantageous if directed towards not only enhancing the endurance capacity of the muscles, but also increasing the cross-sectional area of oblique fast-twitch-fibres. Training should also improve the co-ordination of deep and superficial trunk muscles. These findings may influence physiotherapy and training programs for low back pain patients.

Development and regression of non-capillary vessels in the bovine corpus luteum.

The corpus luteum life cycle is accompanied by capillary growth, maturation and degeneration. Arterial blood vessels are thought to undergo hyperplasia and hypertrophy during the stage of regression, as is the case with non-capillary vessels. In this study, we used morphological studies to show that the development of non-capillary vessels occurs at other corpus luteum stages. Non-capillary vessels were present at the developmental stage of the corpus luteum, and increased markedly in number in the subsequent stages. After double-staining for ASM-1 actin and Ki-67 nuclear antigen, the proliferation of smooth muscle cells (SMCs) was only detected during stages of development and secretion. When the capillaries had disappeared at the regression stage, the arterial blood-vessel walls thickened noticeably. This was attributed to the development of fibroelastosis as shown by staining for collagenous and elastic fibres. In conclusion, the bovine corpus luteum represents a physiological model for studying arteriolization at all stages of development and secretion. At the regression stage, arterioregression sets in.

Limitation of microwave treatment for double immunolabelling with antibodies of the same species and isotype.

Microwave treatment (MW) involves completely blocking contaminating staining in the double-labelling technique, using primary monoclonal antibodies from the same species and the same isotype as well as the same secondary antibody (ab). However, we noticed some limitations when locating proliferating cell types in cryostat and paraffin sections using the advantages presented by MW. Control experiments have shown that MW does not diminish contaminating staining when cytoplasmic (desmin, ASM-1) or nuclear (Ki-67) antigens have been labelled with antibodies in the first round of immunolabelling. In contrast to the cell surface antigen, CD18, where the primary ab had to be crosslinked by a secondary ab to obtain contaminating staining, this was observed for the detection of cytoplasmic or nuclear antigens only labelled with a primary ab. In conclusion, for double immunolabelling with abs from the same species and the same isotype, MW is not able to completely abolish contaminating staining.

Spatiotemporal surface EMG characteristics from rat triceps brachii muscle during treadmill locomotion indicate selective recruitment of functionally distinct muscle regions.

Multichannel surface EMG recordings of a multiheaded skeletal muscle during cyclic locomotion combined with cineradiography were analysed in a chronic experiment. The resulting detailed two-dimensional activation pattern from the long and lateral triceps brachii heads of the rat during treadmill locomotion were combined with gait characteristics and fibre typing of the muscle. Shortly before ground contact of the forelimb, maximum muscle activity was found in the proximal part of the long head of the muscle. During the stance phase maximum activity was observed in the proximal part of the lateral head. The frequency dependent behaviour of cross-covariance functions over both muscle heads confirmed this selective shift in activation. In the lateral triceps brachii head of the investigated rats, exclusively type II fibres were found. In the long head the frequency of type I fibres was the highest in the deep muscle layers, proximally more than distally, whereas type II fibres were dominant in more superficial muscle layers. A combination of physiological and histological findings supports an anticipating mechanism whereby fine-tuning of the vertical foot down manoeuvre is mainly achieved by the (type I fibre dominated) proximal deep compartment of the biarticular long triceps brachii head and force generation is predominantly executed by the monoarticular lateral triceps brachii head.

De Novo Maltotriose Biosynthesis from the Reducing End by Spinacia oleracea L. Chloroplasts.

The distribution of (14)C in the various glucose residues of maltotriose was studied as a function of time of photosynthesis of isolated chloroplasts of spinach (Spinacia oleracea L.) using (14)CO(2). The distribution of label showed that the reducing-end glucose residue was labeled first and the label subsequently distributed to the second and third glucose residues at approximately equal rates.A mechanism for the distribution of label and the synthesis of maltotriose from the reducing end is presented. The mechanism has postulated to be the same as that for the maltose synthase recently described by Schilling. Maltose biosynthesis from alpha-d-glucose-1-phosphate was characterized as involving two glucosyl intermediates by a double displacement mechanism with inversion of configuration. The mode of enzymic action by which maltosyl intermediates were transferred to glucosyl intermediates was consistent with the fractional distribution of radioactivity found in each glucose unit of maltotriose during short term photosynthesis experiments.

Characterization of maltose biosynthesis from α-D-glucose-1-phosphate in Spinacia oleracea. L.

The de novo synthesis of maltose in spinach (Spinacia oleracea L.) was shown to be catalyzed by a maltose synthase, which converts two molecules of α-D-glucose-1-phosphate (α-G1P) (Km 1.5 mmol l(-1)) to maltose and 2 orthophosphate (Pi). This enzyme was purified 203-fold by fractionated ammonium sulfate precipitation and by column chromatography on Sepharose 6B. The addition of α-G1P (15 mmol l(-1)) to the isolation buffer is required to stabilize the enzyme activity during the extraction and purification procedure. Molecular weight determination by gel filtration yielded a value of 95,000. δ-Gluconolactone, ATP and Pi are competitive inhibitors toward the substrate α-G1P. The maltose synthase catalyzes an exchange of the phosphate group of α-G1P with [(32)P] orthophosphate; this transfer reaction suggests that the synthesis of maltose occurs via a glucose-enzyme in a double displacement reaction. The physiological role of this enzyme as a "starch initiator system" is discussed.

Methionine metabolism and ethylene formation in etiolated pea stem sections.

Stem sections of etiolated pea seedlings (Pisum sativum L. cv. Alaska) were incubated overnight on tracer amounts of l-[U-(14)C]methionine and, on the following morning, on 0.1 millimolar indoleacetic acid to induce ethylene formation. Following the overnight incubation, over 70% of the radioactivity in the soluble fraction was shown to be associated with S-methylmethionine (SMM). The specific radioactivity of the ethylene evolved closely paralleled that of carbon atoms 3 and 4 of methionine extracted from the tissue and was always higher than that determined for carbon atoms 3 and 4 of extracted SMM.Overnight incubation of pea stem sections on 1 millimolar methionine enhanced indoleacetic acid-induced ethylene formation by 5 to 10%. Under the same conditions, 1 millimolar homocysteine thiolactone increased ethylene synthesis by 20 to 25%, while SMM within a concentration range of 0.1 to 10 millimolar did not influence ethylene production. When unlabeled methionine or homocysteine thiolactone was applied to stem sections which had been incubated overnight in l-[U-(14)C]methionine, the specific radioactivity of the ethylene evolved was considerably lowered. Application of unlabeled SMM reduced the specific radioactivity of ethylene only slightly.

Interaction of hydrolytic and phosphorolytic enzymes of starch metabolism in Kalanchoë daigremontiana.

The degradation of starch by a protein fraction of Kalanchoë daigremontiana Hamet et Perrier, obtained by ammoniumsulfate precipitation (30-70%), was found to be catalyzed by α-and ß-amylase (EC 3.2.1.1 and EC 3.2.1.2, respectively) and by starch phosphorylase (EC 2.4.1.1). The activity of these enzymes was determined by chromatographic analysis of the reaction products; separation and identification of α-amylase was accomplished by heat-inactivation of ß-amylase and α-glucosidase. When the interaction of amylolytic and phosphorolytic enzymes was comparatively studied, it was found that without inorganic phosphorus in the reaction mixture, (14)C-starch was converted predominantly to maltose and glucose; supplementation with 1-10 mM orthophosphate (Pi) resulted in an increase in glucose-1-phosphate formation and a concomitant reduction of maltose production. Since the total volume of starch degradation remained approximately constant, Pi apparently inhibits ß-amylase (Ki about 3 mM Pi). Thus, free Pi in the cell participates in the regulation of starch catabolism, serving as a substrate for starch phosphorylase while simultaneously reducing the production of maltose. With respect to glucan synthesis, adenosinediphosphoglucose-α-1,4-glucosyltransferase (EC 2.4.1.22), maltose phosphorylase and maltoseglucosyltransferase were also found to be active. The last-named enzyme catalyzes an exchange between dextrins and is considered to provide primer carbohydrates for the synthesis of polyglucans.

Enhancement of ethylene formation by selenoamino acids.

Selenomethionine and selenoethionine enhanced ethylene production in senescing flower tissue of Ipomoea tricolor Cav. and in auxin-treated pea (Pisum sativum L.) stem sections. This enhancement was fully inhibited by the aminoethoxy analog of rhizobitoxine. Methionine did not have a comparable promotive effect, and ethionine partly inhibited ethylene production. When [(14)C]methionine was applied to flower or pea stem tissue followed by treatment with unlabeled selenomethionine or selenoethionine, the specific radioactivity of the ethylene evolved was considerably reduced. The dilution of the specific radioactivity of ethylene by selenomethionine, and in pea stem sections also by selenoethionine, was greater than the dilution by nonradioactive methionine at the same concentration. These results indicate that both selenoamino acids serve as precursors of ethylene and that they are converted to ethylene more efficiently than is methionine.