Effect of a reactive oxygen species-generating system for control of airborne microorganisms in a meat-processing environment

The effectiveness of reactive oxygen species (ROS)-generating AirOcare equipment on the reduction of airborne bacteria in a meat-processing environment was determined. Serratia marcescens and lactic acid bacteria (Lactococcus lactis subsp. lactis and Lactobacillus plantarum) were used to artificially contaminate the air via a six-jet Collison nebulizer. Air in the meat-processing room was sampled immediately after aerosol generation and at various predetermined times at multiple locations by using a Staplex 6 stage air sampler. Approximately a 4-log reduction of the aerial S. marcescens population was observed within 2 h of treatment (P < 0.05) compared to a 1-log reduction in control samples. The S. marcescens populations reduced further by approximately 4.5 log after 24 h of exposure to ROS treatment. Approximately 3-log CFU/m3 reductions in lactic acid bacteria were observed following 2-h ROS exposure. Further ROS exposure reduced lactic acid bacteria in the air; however, the difference in their survival after 24 h of exposure was not significantly different from that observed with the control treatment. S. marcescens bacteria were more sensitive to ROS treatment than the lactic acid bacteria. These findings reveal that ROS treatment using the AirOcare unit significantly reduces airborne S. marcescens and lactic acid bacteria in meat-processing environments within 2 h.

WITHDRAWN: Immunoprophylaxis against important virus diseases of horses, farm animals and birds

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Rapid detection of Salmonella from hydrodynamic pressure-treated poultry using molecular beacon real-time PCR

A real-time polymerase chain reaction (PCR) assay was evaluated to detect Salmonella in hydrodynamic pressure (HDP)-treated chicken using molecular beacon probes available as a commercial kit (iQ-Check, Bio-Rad Laboratories). The sensitivity and accuracy of the assay were compared with the conventional USDA microbiological procedure using artificially contaminated minced chicken. Chicken fillets were irradiated at 10 kGy to completely destroy any naturally occurring Salmonella. These fillets were minced and inoculated with as low as 2+/-1 cfu of S. typhimurium per 25 g chicken. The minced chicken samples were vacuum packed in multi-layer barrier bags, heat shrunk, and treated with HDP. Results showed that all inoculated samples (n=36) were detected by the PCR assay and conventional USDA procedure. Similarly, all uninoculated controls (n=11) were negative by both PCR assay and USDA procedure. As few as 2+/-1 cfu could be detected from 25 g HDP-treated chicken following 16-18 h enrichment in buffered peptone water. Real-time PCR proved to be an effective method for Salmonella detection in HDP-treated chicken with high sensitivity and more importantly, a rapid and high-throughput detection in 18 h, compared to 3-8 days for the conventional microbiological methods. HDP treatment, which has been reported to reduce spoilage bacteria in various meats, was unable to kill pathogenic Salmonella in minced chicken.

Relative efficacy of inactivated bovine herpesvirus-1 (BHV-1) vaccines

The relative efficacy of four commercially available inactivated bovine herpesvirus-1 (BHV-1) vaccines was directly assessed in controlled studies in 5-6-month-old, BHV-1 naïve calves. The sero-response due to the basic course of two intramuscular vaccinations was closely similar for three of four vaccines whereas one vaccine did not induce seroconversion in five of six calves. At the level of challenge virus shedding in nasal mucus, all four vaccines were significantly protective but to a markedly variable degree. Clinically, however, the relative protection ranking of the vaccines was different to that observed for challenge virus shedding. There was no obvious correlation observed between pre-challenge circulating virus neutralising antibody titre and vaccine-induced protection against virus shedding or clinical signs following the intranasal BHV-1 challenge. Present comparative findings suggest that commercially available BHV-1 vaccines are likely to be of variable potency in the natural host.

Modification of active immunization with live bovine herpesvirus 1 vaccine by passive viral antibody

The study in BHV-1 naïve calves investigated the effect of intramuscularly (IM) administered BHV-1 neutralising bovine immunoglobulin on the efficacy of a live intranasally (IN) administered BHV-1 vaccine. Overall on daily basis there was between 40- and 5000-fold less vaccine virus shed by the passively immune calves compared with that shed by the naïve counterparts. The latter seroconverted to the vaccine whereas the virus neutralising (VN) antibody titres in the passively immune calves decreased after vaccination. Compared with unvaccinated naïve or passively immune calves, both groups of vaccinated calves shed significantly less challenge BHV-1 but the daily amount shed was significantly lower in vaccinated naïve calves. The latter were also significantly better protected against pyrexia following the IN BHV-1 challenge compared with vaccinated passively immune calves. Unlike vaccinated calves, clinical reaction to challenge in both unvaccinated groups also involved nasal discharge but the duration of both the nasal discharge and the severe pyrexia was significantly shorter in unvaccinated passively immune calves. Conclusions from the study are: (1) the circulating VN antibody is significantly protective against virus shedding and to alesser extent also against the febrile respiratory disease; (2) the passively immune calves are unlikely to seroconvert after an active infection and (3) the passive antibody does negatively affect vaccine efficacy.

Equine herpesviruses 1 (EHV-1) and 4 (EHV-4) – epidemiology, disease and immunoprophylaxis: A brief review

This review concentrates on the epidemiology, latency and pathogenesis of, and the approaches taken to control infection of horses by equine herpesvirus types 1 (EHV-1) and 4 (EHV-4). Although both viruses may cause febrile rhinopneumonitis, EHV-1 is the main cause of abortions, paresis and neonatal foal deaths. The lesion central to these three conditions is necrotising vasculitis and thrombosis resulting from lytic infection of endothelial cells lining blood capillaries. The initiation of infection in these lesions is likely to be by reactivated EHV-1 from latently infected leukocytes. However, host factors responsible for reactivation remain poorly understood. While vaccine development against these important viruses of equines involving classical and modern approaches has been ongoing for over five decades, progress, compared to other alpha herpesviruses of veterinary importance affecting cattle and pigs, has been slow. However recent data with a live temperature sensitive EHV-1 vaccine show promise.

Characteristics of live bovine herpesvirus-1 vaccines

The common disease caused by bovine herpes virus 1 infection is febrile rhinotracheitis (FRT) and under certain conditions the virus is strongly implicated in pre-disposing cattle to pneumonic pasteurellosis. These illnesses account for a significant economic loss in the cattle industry worldwide and vaccination is widely applied. In naive cattle, and for a short period of time, old and new vaccines significantly reduce clinical signs of FRT and also virus shedding. A single intranasal vaccination affords significant protection in face of maternally derived antibodies, and the protection can be significantly prolonged by a booster intramuscular vaccination. Current data recommend vaccination in face of an outbreak and vaccines appear safe for pregnant cattle.

Variation in immunogenicity of ruminant pestiviruses as determined by the neutralisation assay

Immunogenicity in naive three-month-old Friesian bull calves of nine ruminant pestiviruses, three each of type 1 bovine virus diarrhoea virus (BVDV), type 2 BVDV and border disease virus (BDV) was directly compared in reciprocal cross-neutralisation tests using sera obtained eight weeks after intranasal and intravenous inoculation with live virus. Cytopathic (CP) type 1 BVDV strain C86, non-cytopathic (NCP) type 2 BVDV strain 890 and NCP BDV strain V2536/2 were found to elicit significantly broad cross-neutralising antibodies against viruses in other species whereas other virus strains in all three species produced a much more pronounced homologous and/or species specific response. Results are clearly relevant in the selection of strains for vaccines against diseases caused by these successful, economically important ubiquitous viruses.

Evaluation of a quadrivalent inactivated vaccine for the protection of cattle against diseases due to common viral infections

Efficacy of an inactivated quadrivalent vaccine containing infectious bovine rhinotracheitis (IBR) virus, parainfluenza type 3 (PI3) virus, bovine virus diarrhoea virus (BVDV) and bovine respiratory syncytial virus (BRSV) was assessed in naive bovine calves to evaluate short-term (4-18 weeks) and long-term (24-38 weeks) protection following the basic intramuscular vaccination regime of 2 inoculations a month apart. Vaccination was staggered between the long-term and the short-term groups by about 5 months so that both groups, along with a matched group of 6 unvaccinated (control) calves, could be challenged at the same time. Sequential challenges at intervals of 3-8 weeks were done in the order: IBR virus (intranasally, IN), PI3 virus (IN and intratracheally, IT), pestiviruses (IN) and BRSV (IN and IT). The IBR virus challenge produced febrile rhinotracheitis (FRT) in control calves but both the severity and the duration of FRT was significantly reduced in both vaccinated groups. The amount and the duration of IBR virus shed by the vaccinated groups was significantly reduced compared to the control group. Although PI3 virus, pooled pestivirus and BRSV challenges did not result in a noteworthy disease, challenge virus shedding (amount and duration) from the upper (all 3 viruses) and the lower (BRSV) respiratory tracts was significantly reduced in vaccinated groups. After pestivirus challenge, sera and leukocytes from all control calves were infectious for 6-9 days whereas virus was recovered only from leukocytes in vaccinated calves and only for 1.6-2.7 days. Thus a standard course of the quadrivalent vaccine afforded a significant protection against IBR virus, PI3 virus, BVDV and BRSV for at least 6 months.

Efficacy of a live equine herpesvirus-1 (EHV-1) strain C147 vaccine in foals with maternally-derived antibody: protection against EHV-1 infection

REASONS FOR PERFORMING STUDY

Currently, there is no recommended immunoprophylaxis against febrile respiratory diseases due to equine herpesvirus-1 (EHV-1) and -4 (EHV-4) in horses below age 5-6 months. This is because of interference by maternally-derived antibody (MDA) of vaccines.

OBJECTIVE

Unweaned equine foals are an important reservoir of EHV-1 transmission; therefore, we experimentally assessed the efficacy of a live EHV-1 vaccine in foals age 1.4-3.5 months with MDA.

METHODS

Following vaccination and challenge, parameters assessed were virus shedding in nasal mucus, leucocyte-associated viraemia, circulating virus neutralising antibody activity and clinical reactions.

RESULTS

Controlled challenge showed that a single intranasal dose of the vaccine afforded partial but significant protection against febrile respiratory disease, virus shedding and viraemia due to EHV-1 infection, despite virus-neutralising MDA.

CONCLUSIONS AND POTENTIAL RELEVANCE

The prospective vaccine would be a significant step forward in reducing the incidence of the disease caused by EHV-1 infection.

Shear at twin domain boundaries in YBa2Cu3O7-x

The microstructure and strain state of twin domains in YBa2Cu3O7-x are discussed based upon synchrotron white-beam x-ray microdiffraction measurements. Intensity variations of the fourfold twin splitting of Laue diffraction peaks are used to determine the twin domain structure. Strain analysis shows that interfaces between neighboring twin domains are strained in shear, whereas the interior of these domains are regions of low strain. These measurements are consistent with the orientation relationships of twin boundaries within and across domains and show that basal plane shear stresses can exceed 100 MPa where twin domains meet. Our results support stress field pinning of magnetic flux vortices by twin domain boundaries.

Equid herpesvirus (EHV-1) live vaccine strain C147: efficacy against respiratory diseases following EHV types 1 and 4 challenges

The temperature sensitive and host range mutant clone 147 of equine herpesvirus 1 (EHV-1) was assessed for its ability to protect conventional, susceptible adult horses against respiratory infection by EHV-1 and equine herpesvirus 4 (EHV-4). Intranasal (IN) vaccination with 5.2 log(10) TCID(50) did not cause adverse clinical reactions although a limited virus shedding and viraemia (leukocytes) was observed in 11 of 15 and 10 of 15 vaccinated horses respectively. All 15 vaccinated horses showed a significant seroresponse to both EHV-1 and EHV-4 for virus neutralising (VN) antibody. None of 14 control horses shed virus or became viraemic or seroconverted prior to challenge. EHV-1 challenge (dose 6.0 log(10)) 6 weeks after vaccination resulted in pyrexia in all eight control horses while eight vaccinated horses remained unaffected. Six control horses developed nasal discharge, five of which were mucopurulent nasal discharge (mean duration 3.2 days) which also occurred in four vaccinated horses for 1 day. All eight control horses shed challenge EHV-1 at a significantly higher level (group mean titre 2.6+/-0.4 log(10) TCID(50) per sample) and for much longer (mean duration 4.8+/-1.5 days) than that (group mean titre 1.4+/-0.8 log(10) TCID(50) per sample and mean duration 1.5+/-0.5 days) in six vaccinated horses. Furthermore, all eight control horses became viraemic (mean duration 2.9 days) but viraemia did not occur in eight vaccinated horses. Following EHV-1 challenge, all eight control horses showed a significant VN antibody rise to both EHV-1 and EHV-4 but this occurred in only one vaccinated horse and to EHV-4 only. In EHV-4 challenge (dose of 4.2 log(10) TCID(50)) of a separate pair of seven vaccinated and six control horses, 6 weeks after EHV-1 vaccination resulted in pyrexia (mean duration 2.3 days) and nasal discharge (mean duration 1.8 days) in three and five control horses respectively but the only reaction observed in the vaccinated group was nasal discharge for 1 day in one animal. All six control animals shed virus (mean titre 2.5+/-0.6 log(10) TCID(50) per sample and mean duration 2+/-0.6 days) compared to one vaccinated animal. Although EHV-4 viraemia is rare, 3 of 6 control horses became viraemic after EHV-4 challenge but this was not observed in vaccinated horses. After EHV-4 challenge 3 and 5 of 6 control horses seroconverted for VN antibody to EHV-1 and EHV-4 respectively; a non-responsive control horse had high level of pre-existing VN antibody to EHV-4. However, only 1 of 7 vaccinated horses showed a significant antibody rise and only to EHV-4.

Local plasticity of Al thin films as revealed by x-ray microdiffraction

Grain-to-grain interactions dominate the plasticity of Al thin films and establish effective length scales smaller than the grain size. We have measured large strain distributions and their changes under plastic strain in 1.5-microm-thick Al 0.5% Cu films using a 0.8-microm-diameter white x-ray probe at the Advanced Light Source. Strain distributions arise not only from the distribution of grain sizes and orientation, but also from the differences in grain shape and from stress environment. Multiple active glide plane domains have been found within single grains. Large grains behave like multiple smaller grains even before a dislocation substructure can evolve.

Scanning X-ray microdiffraction with submicrometer white beam for strain/stress and orientation mapping in thin films

Scanning X-ray microdiffraction (microSXRD) combines the use of high-brilliance synchrotron sources with the latest achromatic X-ray focusing optics and fast large-area two-dimensional-detector technology. Using white beams or a combination of white and monochromatic beams, this technique allows for the orientation and strain/stress mapping of polycrystalline thin films with submicrometer spatial resolution. The technique is described in detail as applied to the study of thin aluminium and copper blanket films and lines following electromigration testing and/or thermal cycling experiments. It is shown that there are significant orientation and strain/stress variations between grains and inside individual grains. A polycrystalline film when investigated at the granular (micrometer) level shows a highly mechanically inhomogeneous medium that allows insight into its mesoscopic properties. If the microSXRD data are averaged over a macroscopic range, results show good agreement with direct macroscopic texture and stress measurements.

Derivation and characterisation of a live equid herpes virus-1 (EHV-1) vaccine to protect against abortion and respiratory disease due to EHV-1

A German abortion isolate of EHV-1 (strain M8) was grown in equine dermal (ED) cells at a low multiplicity of infection in presence of 5-bromo-2-deoxy uridine. The resulting stock was dialysed, titrated and cloned by terminal dilution in ED cells grown in 96-well microtitration plates. Of 192 clones each originating from a single focus, clone 147 (C147) was found to be restricted for growth at and above temperatures of 38.5 degrees C. It was also restricted for growth at 37 degrees C in rabbit kidney (RK-13) cells which are widely used for the isolation and titration of EHV-1; hence clone 147 was EHV-4-like. Clone 147 showed a remarkable efficacy as a vaccine in protecting conventional pregnant Welsh Mountain pony mares against abortions due to EHV-1. A single intranasal (IN) vaccination protected five out of six (83.3%), and four out of five (80%) of mares upon challenge 4 and 5-6 months, respectively, after the immunisation, whereas all six unvaccinated mares aborted between 9 and 19 days after IN EHV-1 challenge. With the exception of the day 9 abortion, foetuses of the remaining five mares were EHV-1 infected. Placenta from the early aborting mare was, however, EHV-1 positive. Both groups of vaccinated mares were also significantly protected against clinical reaction (notably pyrexia), nasal shedding and viraemia following challenge infection.

Prevention of transplacental infection of bovine foetus by bovine viral diarrhoea virus through vaccination

Results are presented for an experimental validation of the efficacy of an EU licensed, inactivated bovine viral diarrhoea virus vaccine (Bovilis BVDV). This study was designed to assess the quality of efficacy 6 months after a single course of vaccination (two intramuscular doses a month apart). A natural challenge at about 87 days of gestation by 3 persistently infected carrier heifers rapidly infected all experimental heifers. This resulted in transplacental BVDV infection of all 7 unvaccinated dams whereas 11 immunised dams produced 9 live-born calves and 2 aborted foetuses from which no BVDV could be recovered.

PKA accelerates rate of force development in murine skinned myocardium expressing alpha- or beta-tropomyosin

In myocardium, protein kinase A (PKA) is known to phosphorylate troponin I (TnI) and myosin-binding protein-C (MyBP-C). Here, we used skinned myocardial preparations from nontransgenic (NTG) mouse hearts expressing 100% alpha-tropomyosin (alpha-Tm) to examine the effects of phosphorylated TnI and MyBP-C on Ca2+ sensitivity of force and the rate constant of force redevelopment (k(tr)). Experiments were also done using transgenic (TG) myocardium expressing approximately 60% beta-Tm to test the idea that the alpha-Tm isoform is required to observe the mechanical effects of PKA phosphorylation. Compared with NTG myocardium, TG myocardium exhibited greater Ca2+ sensitivity of force and developed submaximal forces at faster rates. Treatment with PKA reduced Ca2+ sensitivity of force in NTG and TG myocardium, had no effect on maximum k(tr) in either NTG or TG myocardium, and increased the rates of submaximal force development in both kinds of myocardium. These results show that PKA-mediated phosphorylation of myofibrillar proteins significantly alters the static and dynamic mechanical properties of myocardium, and these effects occur regardless of the type of Tm expressed.

Cooperative mechanisms in the activation dependence of the rate of force development in rabbit skinned skeletal muscle fibers

Regulation of contraction in skeletal muscle is a highly cooperative process involving Ca(2+) binding to troponin C (TnC) and strong binding of myosin cross-bridges to actin. To further investigate the role(s) of cooperation in activating the kinetics of cross-bridge cycling, we measured the Ca(2+) dependence of the rate constant of force redevelopment (k(tr)) in skinned single fibers in which cross-bridge and Ca(2+) binding were also perturbed. Ca(2+) sensitivity of tension, the steepness of the force-pCa relationship, and Ca(2+) dependence of k(tr) were measured in skinned fibers that were (1) treated with NEM-S1, a strong-binding, non-force-generating derivative of myosin subfragment 1, to promote cooperative strong binding of endogenous cross-bridges to actin; (2) subjected to partial extraction of TnC to disrupt the spread of activation along the thin filament; or (3) both, partial extraction of TnC and treatment with NEM-S1. The steepness of the force-pCa relationship was consistently reduced by treatment with NEM-S1, by partial extraction of TnC, or by a combination of TnC extraction and NEM-S1, indicating a decrease in the apparent cooperativity of activation. Partial extraction of TnC or NEM-S1 treatment accelerated the rate of force redevelopment at each submaximal force, but had no effect on kinetics of force development in maximally activated preparations. At low levels of Ca(2+), 3 microM NEM-S1 increased k(tr) to maximal values, and higher concentrations of NEM-S1 (6 or 10 microM) increased k(tr) to greater than maximal values. NEM-S1 also accelerated k(tr) at intermediate levels of activation, but to values that were submaximal. However, the combination of partial TnC extraction and 6 microM NEM-S1 increased k(tr) to virtually identical supramaximal values at all levels of activation, thus, completely eliminating the activation dependence of k(tr). These results show that k(tr) is not maximal in control fibers, even at saturating [Ca(2+)], and suggest that activation dependence of k(tr) is due to the combined activating effects of Ca(2+) binding to TnC and cross-bridge binding to actin.

Cross-bridge interaction kinetics in rat myocardium are accelerated by strong binding of myosin to the thin filament

To determine the ability of strong-binding myosin cross-bridges to activate the myocardial thin filament, we examined the Ca2+ dependence of force and cross-bridge interaction kinetics at 15 degrees C in the absence and presence of a strong-binding, non-force-generating derivative of myosin subfragment-1 (NEM-S1) in chemically skinned myocardium from adult rats. Relative to control conditions, application of 6 microM NEM-S1 significantly increased Ca2+-independent tension, measured at pCa 9.0, from 0.8 +/- 0.3 to 3.7 +/- 0.8 mN mm-2. Furthermore, NEM-S1 potentiated submaximal Ca2+-activated forces and thereby increased the Ca2+ sensitivity of force, i.e. the [Ca2+] required for half-maximal activation (pCa50) increased from pCa 5.85 +/- 0.05 to 5.95 +/- 0.04 (change in pCa50 (dpCa50) = 0.11 +/- 0.02). The augmentation of submaximal force by NEM-S1 was accompanied by a marked reduction in the steepness of the force-pCa relationship for forces less than 0.50 Po (maximum Ca2+-activated force), i.e. the Hill coefficient (n2) decreased from 4.72 +/- 0.38 to 1.54 +/- 0.07. In the absence of NEM-S1, the rate of force redevelopment (ktr) was found to increase from 1.11 +/- 0.21 s-1 at submaximal [Ca2+] (pCa 6.0) to 9.28 +/- 0.41 s-1 during maximal Ca2+ activation (pCa 4.5). Addition of NEM-S1 reduced the Ca2+ dependence of ktr by eliciting maximal values at low levels of Ca2+, i.e. ktr was 9.38 +/- 0.30 s-1 at pCa 6.6 compared to 9.23 +/- 0.27 s-1 at pCa 4. At intermediate levels of Ca2+, ktr was less than maximal but was still greater than values obtained at the same pCa in the absence of NEM-S1. NEM-S1 dramatically reduced both the extent and rate of relaxation from steady-state submaximal force following flash photolysis of the caged Ca2+ chelator diazo-2. These data demonstrate that strongly bound myosin cross-bridges increase the level of thin filament activation in myocardium, which is manifested by an increase in the rate of cross-bridge attachment, potentiation of force at low levels of free Ca2+, and slowed rates of relaxation.

Polyamines decrease Ca(2+) sensitivity of tension and increase rates of activation in skinned cardiac myocytes

Owing in part to their interactions with membrane proteins, polyamines (e.g., spermine, spermidine, and putrescine) have been identified as potential modulators of membrane excitability and Ca(2+) homeostasis in cardiac myocytes. To investigate whether polyamines also affect cardiac myofilament proteins, we assessed the effects of polyamines on contractility using rat myocytes and trabeculae that had been permeabilized with Triton X-100. Spermine, spermidine, and putrescine reversibly increased the [Ca(2+)] required for half-maximal tension (i.e., right-shifted tension pCa curves), with the following order of efficacy: spermine (+4) > spermidine (+3) > putrescine (+2). However, synthetic analogs that differed from spermine in charge distribution were not as effective as spermine in altering isometric tension. None of the polyamines had a significant effect on maximal tension, except at high concentrations. After flash photolysis of DM-Nitrophen (a caged Ca(2+) chelator), spermine accelerated the rate of tension development at low and intermediate but not high [Ca(2+)]. These results indicate that polyamines, especially spermine, interact with myofilament proteins to reduce apparent Ca(2+) binding affinity and speed cross-bridge cycling kinetics at submaximal [Ca(2+)].

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.

Impaired cardiomyocyte relaxation and diastolic function in transgenic mice expressing slow skeletal troponin I in the heart

1. To assess the specific functions of the cardiac isoform of troponin I (cTnI), we produced transgenic mice that expressed slow skeletal troponin I (ssTnI) specifically in cardiomyocytes. Cardiomyocytes from these mice displayed quantitative replacement of cTnI with transgene-encoded ssTnI. 2. The ssTnI transgenic mice were viable and fertile and did not display increased mortality or detectable cardiovascular histopathology. They exhibited normal ventricular weights and heart rates. 3. Permeabilized transgenic cardiomyocytes demonstrated an increased Ca2+ sensitivity of tension and a lack of contractile responsiveness to cAMP-dependent protein kinase (PKA). Isolated cardiomyocytes from transgenic mice had normal velocities of unloaded shortening but unlike wild-type controls exhibited no enhancement of the velocity of shortening in response to treatment with isoprenaline. Transgenic cardiomyocytes exhibited greater extents of shortening than non-transgenic cardiomyocytes at baseline and after treatment with isoprenaline. 4. The rates of rise of intracellular [Ca2+] and the peak amplitudes of the intracellular [Ca2+] transients were similar in transgenic and wild-type myocytes. However, the half-time of intracellular [Ca2+] decay was significantly greater in the transgenic myocytes. This change in decay of intracellular [Ca2+] was correlated with an increase in the re-lengthening time of the transgenic cells. 5. These changes in cardiomyocyte function in vitro were manifested in vivo as impaired diastolic function both at baseline and after stimulation with isoprenaline. 6. Thus, cTnI has important roles in regulating the Ca2+ sensitivity of cardiac myofibrils and controlling cardiomyocyte relaxation and cardiac diastolic function. cTnI is also required for the normal responsiveness of cardiomyocytes to beta-adrenergic receptor stimulation.