Reticulum Motility Research Articles

Dexmedetomidine and xylazine in sheep: A study of cardiopulmonary, hematological, and gastrointestinal effects

The study aimed to compare the cardiopulmonary, hematological, and gastrointestinal effects of doses of xylazine and dexmedetomidine capable of promoting moderate sedation in sheep. Seven mixed-breed, healthy sheep underwent a crossover study with dexmedetomidine 0.005 mg.kg−1 (DEX) and xylazine 0.075 mg.kg−1 (XYL) intravenously. Sedation onset time, sedation score, heart rate (HR), respiratory rate (RR), systolic (SBP), mean (MBP), and diastolic (DBP) blood pressure, and spleen thickness were evaluated before treatment administration (baseline - T0) and 5 (T5), 15 (T15), 30 (T30), 45 (T45), and 60 (T60) minutes after sedation. Red blood cell (RBC), total plasma proteins (TPP), glycemia, lactatemia, and urine density were evaluated at T0, T5, T15, T30, and T60; rumen (RuM) and reticulum (ReM) motility were evaluated at T0, T15, T30, T45, and T60. The treatments promoted similar sedation scores at all time points (p > 0.05), with early onset of action of XYL (71 ± 16" vs 111 ± 33"). HR in DEX (63 ± 9 bpm) was lower than in XYL (83 ± 16 bpm) at T5 (p < 0.05). Blood pressure varied throughout the evaluation times and between treatments. There was an increase in spleen thickness at T30, coinciding with the lowest packed cell volume values, in both treatments. Values of platelet count, total leukocytes, and TPP were reduced compared to T0, but with no difference between treatments. RuM, ReM, and urine density reduced in both treatments, but the return to baseline values happened earlier with XYL. We concluded that both xylazine (0.075 mg.kg−1) and dexmedetomidine (0.005 mg.kg−1) promote splenic RBC sequestration and a significant reduction in rumen and reticulum motility when administered intravenously. Xylazine has an early onset of action and causes a significant increase in heart rate. Dexmedetomidine, on the other hand, has a later onset of action and a prolonged effect on sedation, urinary density, rumen motility, and reticulum motility.

Junctional sarcoplasmic reticulum motility in adult mouse ventricular myocytes.

Excitation-contraction (EC) coupling is the coordinated process by which an action potential triggers cardiac myocyte contraction. EC coupling is initiated in dyads where the junctional sarcoplasmic reticulum (jSR) is in tight proximity to the sarcolemma of cardiac myocytes. Existing models of EC coupling critically depend on dyad stability to ensure the fidelity and strength of EC coupling, where even small variations in ryanodine receptor channel and voltage-gated calcium channel-α 1.2 subunit separation dramatically alter EC coupling. However, dyadic motility has never been studied. Here, we developed a novel strategy to track specific jSR units in dissociated adult ventricular myocytes using photoactivatable fluorescent proteins. We found that the jSR is not static. Instead, we observed dynamic formation and dissolution of multiple dyadic junctions regulated by the microtubule-associated molecular motors kinesin-1 and dynein. Our data support a model where reproducibility of EC coupling results from the activation of a temporally averaged number of SR Ca2+ release units forming and dissolving SR-sarcolemmal junctions. These findings challenge the long-held view that the jSR is an immobile structure and provide insights into the mechanisms underlying its motility.

Opaque1 Encodes a Myosin XI Motor Protein That Is Required for Endoplasmic Reticulum Motility and Protein Body Formation in Maize Endosperm

Myosins are encoded by multigene families and are involved in many basic biological processes. However, their functions in plants remain poorly understood. Here, we report the functional characterization of maize (Zea mays) opaque1 (o1), which encodes a myosin XI protein. o1 is a classic maize seed mutant with an opaque endosperm phenotype but a normal zein protein content. Compared with the wild type, o1 endosperm cells display dilated endoplasmic reticulum (ER) structures and an increased number of smaller, misshapen protein bodies. The O1 gene was isolated by map-based cloning and was shown to encode a member of the plant myosin XI family (myosin XI-I). In endosperm cells, the O1 protein is associated with rough ER and protein bodies. Overexpression of the O1 tail domain (the C-terminal 644 amino acids) significantly inhibited ER streaming in tobacco (Nicotiana benthamiana) cells. Yeast two-hybrid analysis suggested an association between O1 and the ER through a heat shock protein 70-interacting protein. In summary, this study indicated that O1 influences protein body biogenesis by affecting ER morphology and motility, ultimately affecting endosperm texture.

A Mechanism of Excessive Accumulation of Abomasal Gas in Vagotomized Cattle Determined using Fluoroscopy

To better understand the mechanism of excessive gas accumulation in the abomasum in bovine abomasal displacement, we performed gastric fluoroscopy in vagotomized cattle. Fifteen 6-month-old Holstein steers were divided into three groups: a non-vagotomized control group (Group C; n=5), a ventral thoraco-vagotomized group (Group V; n=5), and a dorsal and ventral thoraco-vagotomized group (Group DV; n=5). These groups were examined by fluoroscopy before and during a 5-week observation period after surgery. In Group C, no change was observed throughout the observation period. In Group DV, immediately after surgery, reticuloruminal motility was completely absent and ruminal distention was seen. Two weeks after surgery, abnormal reticulum motility and increased gas accumulation in the abomasal body were noted. Abomasal dilatation was also observed. In Group V, 1 week after surgery, gas inflow into the abomasum and relatively normal reticulum motility were observed along with a rapid increase in abomasal gas. Abomasal dilatation was also observed. In addition, left-displaced abomasum occurred in one of the steers in this group. From these results, we concluded that one of the mechanisms of excessive gas accumulation in the abomasum is reticulum-mediated gas inflow from the rumen combined with vagotomy-induced hypomotility.

Myosin-dependent endoplasmic reticulum motility and F-actin organization in plant cells

Plants exhibit an ultimate case of the intracellular motility involving rapid organelle trafficking and continuous streaming of the endoplasmic reticulum (ER). Although it was long assumed that the ER dynamics is actomyosin-driven, the responsible myosins were not identified, and the ER streaming was not characterized quantitatively. Here we developed software to generate a detailed velocity-distribution map for the GFP-labeled ER. This map revealed that the ER in the most peripheral plane was relatively static, whereas the ER in the inner plane was rapidly streaming with the velocities of up to approximately 3.5 microm/sec. Similar patterns were observed when the cytosolic GFP was used to evaluate the cytoplasmic streaming. Using gene knockouts, we demonstrate that the ER dynamics is driven primarily by the ER-associated myosin XI-K, a member of a plant-specific myosin class XI. Furthermore, we show that the myosin XI deficiency affects organization of the ER network and orientation of the actin filament bundles. Collectively, our findings suggest a model whereby dynamic three-way interactions between ER, F-actin, and myosins determine the architecture and movement patterns of the ER strands, and cause cytosol hauling traditionally defined as cytoplasmic streaming.

Effects and mechanisms of action of the ergopeptides ergotamine and ergovaline and the effects of peramine on reticulum motility of sheep

To investigate effects and mechanisms of ergotamine and ergovaline and effects of peramine on reticulum motility of sheep. 3 sheep with indwelling electrodes in the reticulum and samples of reticulum collected from 126 sheep at an abattoir. In conscious sheep, motility was recorded as integrated electromyograms from the reticulum. Ergotamine was administered IV alone or in combination with the cholinergic muscarinic receptor antagonist atropine to sheep, and motility of the reticulum was assessed. In vitro, whole wall strips of the reticulum, cut in a direction to record longitudinal muscle activity via force transducers, were placed in 10-mL organ baths and superfused with Tyrode Ringer's solution at 37 degrees C and oxygenated with 95% oxygen and 5% carbon dioxide. Testing involved incubation of reticulum strips with ergotamine, ergovaline, and peramine and measurement of motility of the reticulum tissues. Administration of ergotamine to sheep reduced the frequency of reticulum contractions and increased baseline electromyographic activity (tonus). Frequency was unaffected by atropine, whereas tonus was significantly reduced. In vitro, ergotamine and ergovaline increased tonic contractions and stimulated phasic contractions of reticulum tissues and potentiated electrically stimulated contractions. Atropine and tetrodotoxin reduced tonic contractions, but stimulation of large-amplitude phasic contractions remained. Peramine had no effect on motility of reticulum tissues. Results of the study indicated that peripheral excitatory effects of the ergopeptides on motility of the reticulum appear to be mediated partly through myenteric neurons and muscarinic receptors and also through direct effects on the muscles.

Agonist-induced regulation of mitochondrial and endoplasmic reticulum motility

Using fluorescently tagged markers for organelles in conjunction with confocal microscopy, we have studied the effects of agonist-induced Ca2+ signals on the motility of mitochondria and the ER (endoplasmic reticulum). We observed that the muscarinic agonist carbachol produced a rapid, simultaneous and reversible cessation of the movements of both organelles, which was dependent on a rise in cytosolic Ca2+. This rise in Ca2+ was shown to cause a fall in cellular ATP levels, and the effect of carbachol on organelle movement could be mimicked by depleting ATP with metabolic inhibitors in the absence of any such rise in Ca2+. However, a Ca2+-sensing process independent of ATP appears also to be involved, because we identified conditions where the ATP depletion was blocked (by inhibitors of the Ca2+ pumps), but the organelle movements still ceased following a rise in cytosolic Ca2+. We conclude that the co-ordinated cessation of mitochondria and ER motility is a process regulated by the cytosolic concentration of both Ca2+ and ATP, and that these two parameters are likely to synergize to regulate the localization of the two organelles, and to facilitate the transfer of Ca2+ between them.

Microtubule-based endoplasmic reticulum motility in Xenopus laevis: activation of membrane-associated kinesin during development.

The endoplasmic reticulum (ER) in animal cells uses microtubule motor proteins to adopt and maintain its extended, reticular organization. Although the orientation of microtubules in many somatic cell types predicts that the ER should move toward microtubule plus ends, motor-dependent ER motility reconstituted in extracts of Xenopus laevis eggs is exclusively a minus end-directed, cytoplasmic dynein-driven process. We have used Xenopus egg, embryo, and somatic Xenopus tissue culture cell (XTC) extracts to study ER motility during embryonic development in Xenopus by video-enhanced differential interference contrast microscopy. Our results demonstrate that cytoplasmic dynein is the sole motor for microtubule-based ER motility throughout the early stages of development (up to at least the fifth embryonic interphase). When egg-derived ER membranes were incubated in somatic XTC cytosol, however, ER tubules moved in both directions along microtubules. Data from directionality assays suggest that plus end-directed ER tubule extensions contribute approximately 19% of the total microtubule-based ER motility under these conditions. In XTC extracts, the rate of ER tubule extensions toward microtubule plus ends is lower ( approximately 0.4 microm/s) than minus end-directed motility ( approximately 1.3 microm/s), and plus end-directed motility is eliminated by a function-blocking anti-conventional kinesin heavy chain antibody (SUK4). In addition, we provide evidence that the initiation of plus end-directed ER motility in somatic cytosol is likely to occur via activation of membrane-associated kinesin.

Cytoskeleton and PCH-induced pigment aggregation in Macrobrachium potiuna erythrophores.

Herein we report the effects of microtubule- and actin-like filament disrupting drugs, as well as the microtubule stabilizer taxol, on PCH-induced pigment granule aggregation within erythrophores of the freshwater crustacean Macrobrachium potiuna. Dose-response curves (DRCs) to the pigment-concentrating hormone PCH were determined under control and experimental conditions to evaluate the effects elicited by the cytoskeleton-affecting drugs. Colchicine, at temperatures 22 degrees C and 4 degrees C, and vinblastine significantly inhibited the aggregating response to PCH and affected the dynamics of the process, as shown by the change in the slope of the regression curve calculated from the DRCs. Lumicolchicine, a colchicine analogue with no affinity for tubulin, also inhibited pigment migration, though no change in the slope of the regression curve was observed. The inhibitory effects of lumicolchicine demonstrate that changes in sites other than cytoskeleton, such as membrane permeability, may also cause a decrease in the PCH-induced aggregating responses and that the colchicine effects may result from its action on cellular sites additional to the cytoskeleton. Taxol, a microtubule stabilizer, did not affect the DRC to PCH, and DMSO improved the PCH-evoked responses, pointing out to the maintenance of tubulin in the polymerized state as the appropriate condition for aggregation. Cytochalasin B, an actin-like filament disrupter, diminished the aggregating responses to the hormone, with no change in the slope of the regression curve, indicating that these elements take part in the process and that cytosolic calcium rise, sol/gel transformations and endoplasmic reticulum motility may well play an important role in granule migration. It is suggested that microtubules are steadily polymerized as a requirement for pigment aggregation and that process is biphasic, the initial phase being dependent on the microtubule integrity.

Influence of intravascular infusion of short-chain fatty acids on forestomach motility of sheep not receiving food

Intrahepatic portal and intrajugular infusions of short-chain fatty acids (SCFA) (as sodium acetate, propionate and butyrate) singly and mixed were given to unfed adult sheep. Reticulum motility was significantly inhibited by 3-h infusions of a mixture of the three SCFA at 4 mmol min −1 and by propionate alone at 1.2 and 2.0 mmol min −1 via jugular or hepatic portal route. Rumination was also inhibited by those infusions and additionally by the mixture at 2 mmol min −1 and by acetate at 2.2 mmol min −1, the latter via the portal route. α-1 and α-2 adrenoreceptor antagonists did not reverse the effect of propionate when administered during a period of inhibition. Rapid i.v. adrenaline injection during a period of inhibition induced a single biphasic contraction of the reticulum. Vagal efferent stimulation under general anaesthesia during intraportal propionate infusion always caused reticulum contraction. Propionate reduced motility by acting at an unknown site in the reflex control system, not by paralysis of the muscle or over activation of the sympathetic system. Normal plasma concentrations would not of themselves cause severe inhibition of motility, but could contribute to this multifactorial control system. Rumination was more sensitive than resting motility cycles to the inhibitory effect.

Effects of a parasympathomimetic agent, slaframine, on reticulo-omasal orifice function

Three nonlactating, nonpregnant, ruminally cannulated Holstein cows (680–732 kg) fed chopped brome hay ad libitum once daily were used to study effects of slaframine (SF) on rumen function in a 3 × 3 Latin square design. Animals were injected intramuscularly with 0, 20 or 40 μg kg BW−1 SF, allowing for 1 d between trials. At 0, 40, 180 and 360 min postinjection rumen contents were partially evacuated. Reticular contraction frequency (RCF) was determined using a balloon placed in the reticulum connected to a pressure transducer and physiograph and reticulo-omasal orifice opening duration (ROOD) was measured using palpation and endoscopy. RCF as a percentage of predose was decreased linearly by SF treatment (P &lt; 0.01). SF affected ROOD, which was higher (P &lt; 0.05) for both SF treatments. This pattern was also linear (P &lt; 0.01). A characteristic change in reticulum pressure was identified that correlated with SF mediated variation in ROOD (r = 0.67; P &lt; 0.01). Previous research has indicated that SF administration increased salivation and shifted site of digestion. The results presented herein are consistent with these observations and indicate that duration of reticulo-omasal orifice opening may be more highly associated with the rate of digesta passage than reticular frequency. Key words: Slaframine, reticulo-omasal orifice, reticulum motility, cattle

Influences of cold exposure on digestion of organic matter, rates of passage of digesta in the gastrointestinal tract, and feeding and rumination behaviour in sheep given four forage diets in the chopped, or ground and pelleted form.

Sixteen sheep, each fitted with cannulas in the rumen and proximal duodenum, were given four diets in the chopped or ground and pelleted form, at fixed intakes at intervals of 2 h. The sheep were closely shorn and exposed to temperatures of 22-25 degrees or 1-4 degrees for four periods of 45 d. Flow of duodenal digesta by reference to the markers CoEDTA and 103Ru-phenanthroline, chewing behaviour and particle size of rumen and duodenal digesta were measured. Apparent digestibility of organic matter (OM) in the gastrointestinal tract was depressed (P less than 0.05) by grinding and pelleting the diet, and by exposure of sheep to cold ambient temperatures. This was attributable to depression (P less than 0.01) by 0.1 of OM digestion in the reticulo-rumen. No effects on intestinal digestion of OM were observed. Cold ambient temperatures did not affect the content, but increased the rate of digestion for pelleted diets but not for chopped diets, of potentially-degradable cell-wall constituents of ground dietary material incubated in nylon-bags in the rumen. Retention times of markers of the particulate and liquid phases of rumen digesta were not significantly (P less than 0.05) affected by ambient temperature, despite significant (P less than 0.001) increases in the rate of contraction of the reticulum. Retention time of 103Ru-phenanthroline in the intestines was not affected by cold exposure. Cold exposure was associated with depression (P less than 0.05) of volatile fatty acids concentration in the rumen and elevated (P less than 0.05)pH. Molar proportions of acetic and isovaleric acid were reduced (P less than 0.01), accompanied by increased (P less than 0.001) proportions of propionic acid during cold exposure. Cold exposure and pelleting of the diets were both associated with reduction in digesta particle size in the rumen. Duodenal particle size was not affected by cold exposure. Pelleting of the diet markedly reduced (P less than 0.001) duration of chewing and number of chews/d during eating and rumination. Cold exposure of sheep resulted in a faster (P less than 0.01) rate of eating of the diets. When allowed to express their voluntary feed consumption during a 10 d period, intakes of chopped diets were increased by 0.13 (P less than 0.01) by cold exposure, in contrast to lack of significant change in sheep given pellets.(ABSTRACT TRUNCATED AT 400 WORDS)

RETICULAR MYOELECTRIC ACTIVITY AND TURNOVER OF RUMEN DIGESTA IN THE GROWING STEER

Myoelectric activity and digesta turnover was measured in the forestomach of steers adapted to diets varying in proportions of hay and concentrates. Frequencies of reticular spike bursts were positively related to turnover rates of liquid rumen digesta. Variations in these processes were induced by changes in diet composition. Key words: Cattle, reticulum motility, digesta turnover

The application of cumulative sum analysis to the investigation of reticulum motility in ruminant animals.

SummaryA method of analysing reticulum motility recordings is described which is based on cumulative sum analysis of the cycle intervals. Its application to the results of an experiment in which the motility was inhibited by intraduodenal long chain fatty acids is used to show its value. The problems associated with forestomach motility analysis are discussed in relation to these experimental results.ZusammenfassungDie Anwendung der kumulativen Summen‐Analyse bei der Untersuchung der Reticulum‐Motilität von WiederkäuernEs wird eine Methode zur Analyse der Reticulum‐Motilität beschrieben, die auf der Auswertung der Summenhäufigkeit von Zyklusintervallen beruht. Der Wert dieses Verfahrens wird anhand einer experimentellen Motilitätshemmung durch intraduodenale Infusion von langkettigen Fettsäuren gezeigt. Die mit der Analyse der Vormagenmotilität vergesellschafteten Probleme werden aufgrund dieser experimentellen Ergebnisse diskutiert.RésuméUtilisation de l'analyse des sommes cumulées lors de l'examen de la mobilité du Reticulum chez des ruminantsUne méthode d'analyse de la mobilité du Reticulum est décrite sur la base de l'interprétation de fréquence des sommes des intervalles de cycle. La valeur de cette méthode est montrée en fonction d'une inhibition expérimentale de la mobilité par une infusion intraduodénale d'acides gras à longues chaînes. Les problèmes rencontrés avec l'analyse de la mobilité du réseau sont discutés en fonction des résultats expérimentaux.ResumenLa aplicación del análisis cumulativo de las sumas en el estudio de la motilidad del bonete en los animales rumiantesSe describe una técnica para analizar la motilidad del bonete, la cual se basa en la evaluación de la frecuencia de las sumas de los intervalos de ciclo. El valor de este procedimiento se demuestra con ayuda de la inhibición experimental de la motilidad mediante infusión intraduodenal de ácidos grasos de cadena larga. A la vista de estos resultados experimentales, se discuten los problemas relacionados con el análisis de la motilidad de los preestómagos.