HTS driven by fluorescence lifetime detection of FRET identifies activators and inhibitors of cardiac myosin

Small molecules that bind to allosteric sites on target proteins to alter protein function are highly sought in drug discovery. High-throughput screening (HTS) assays are needed to facilitate the direct discovery of allosterically active compounds. We have developed technology for high-throughput time-resolved fluorescence lifetime detection of fluorescence resonance energy transfer (FRET), which enables the detection of allosteric modulators by monitoring changes in protein structure. We tested this approach at the industrial scale by adapting an allosteric FRET sensor of cardiac myosin to high-throughput screening (HTS), based on technology provided by Photonic Pharma and the University of Minnesota, and then used the sensor to screen 1.6 million compounds in the HTS facility at Bristol Myers Squibb. The results identified allosteric activators and inhibitors of cardiac myosin that do not compete with ATP binding, demonstrating high potential for FLT-based drug discovery.

Abstract P421: Analysis Of The Functional Relevance Of Human Beta-myosin Heavy Chain Post-translational Modifications

Sarcomeric proteins have been shown to be a target of post-translational modifications (PTMs). Phosphorylation and acetylation of several sarcomeric proteins have been reported to be important for fine-tuning of myocardial contractility. Given the emerging importance of understanding the potential role of PTMs on cardiac muscle performance in healthy and diseased states, we sought to identify novel PTMs on human cardiac beta-myosin heavy chain (beta-MHC). We found several high confidence beta-MHC peptides modified by K-acetylation and S- and T-phosphorylation found in non-diseased, ischemic, and non-ischemic human heart samples. Using bottom-up proteomics and label-free quantification, we identified seven high-confidence peptides (K34, K58, S210, T215, K429, K951, K1195) with K951 displaying significant reduction in acetylation levels in both ischemic and non-ischemic failing hearts compared to donor hearts. Molecular dynamics simulations were performed to better understand the functional significance of the beta-MHC PTMs. Focus was placed on modifications in the regions with greatest potential functional significance as well as modified residues with significantly altered abundance in diseased states (K951-Ac at the myosin tail nearby a binding site for myosin heads in the super-relaxed state). K951 is located in the myosin tail (S2) at the C-terminal end of simulated structure. In both unmodified and modified simulations, the tail fragment showed significant flexibility and partial unfolding at the C-terminus. In the unmodified simulations, the inter- and intra-helical contacts were maintained. However, when beta-MHC is acetylated at residue 951, these helical contacts were altered as the uncharged acetylated residue no longer formed strong hydrogen bonds with a residue of the opposite chain. This facilitated changes increase in inter-helical contacts, an increase in inter-helical distance, and disruption of the coiled-coil tail domain structure. Our study suggests that there are distinct differences in beta-MHC acetylation levels that appear to be influenced more by location of the modified residues than the type of heart disease (ischemic- and non-ischemic heart failure). Additionally, we speculate that these PTMs have the potential to modulate the interactions between beta-MHC and other regulatory sarcomeric proteins, as well as ADP-release rate of myosin, flexibility of S2 fragment, and cardiac myofilament contractility under normal and heart failure condition.

Identical and Nonidentical Twins: Risk and Factors Involved in Development of Islet Autoimmunity and Type 1 Diabetes

OBJECTIVE

There are variable reports of risk of concordance for progression to islet autoantibodies and type 1 diabetes in identical twins after one twin is diagnosed. We examined development of positive autoantibodies and type 1 diabetes and the effects of genetic factors and common environment on autoantibody positivity in identical twins, nonidentical twins, and full siblings.

RESEARCH DESIGN AND METHODS

Subjects from the TrialNet Pathway to Prevention Study (N = 48,026) were screened from 2004 to 2015 for islet autoantibodies (GAD antibody [GADA], insulinoma-associated antigen 2 [IA-2A], and autoantibodies against insulin [IAA]). Of these subjects, 17,226 (157 identical twins, 283 nonidentical twins, and 16,786 full siblings) were followed for autoantibody positivity or type 1 diabetes for a median of 2.1 years.

RESULTS

At screening, identical twins were more likely to have positive GADA, IA-2A, and IAA than nonidentical twins or full siblings (all P < 0.0001). Younger age, male sex, and genetic factors were significant factors for expression of IA-2A, IAA, one or more positive autoantibodies, and two or more positive autoantibodies (all P ≤ 0.03). Initially autoantibody-positive identical twins had a 69% risk of diabetes by 3 years compared with 1.5% for initially autoantibody-negative identical twins. In nonidentical twins, type 1 diabetes risk by 3 years was 72% for initially multiple autoantibody-positive, 13% for single autoantibody-positive, and 0% for initially autoantibody-negative nonidentical twins. Full siblings had a 3-year type 1 diabetes risk of 47% for multiple autoantibody-positive, 12% for single autoantibody-positive, and 0.5% for initially autoantibody-negative subjects.

CONCLUSIONS

Risk of type 1 diabetes at 3 years is high for initially multiple and single autoantibody-positive identical twins and multiple autoantibody-positive nonidentical twins. Genetic predisposition, age, and male sex are significant risk factors for development of positive autoantibodies in twins.

Low-Dose Anti-Thymocyte Globulin (ATG) Preserves β-Cell Function and Improves HbA1c in New-Onset Type 1 Diabetes

OBJECTIVE

A pilot study suggested that combination therapy with low-dose anti-thymocyte globulin (ATG) and pegylated granulocyte colony-stimulating factor (GCSF) preserves C-peptide in established type 1 diabetes (T1D) (duration 4 months to 2 years). We hypothesized that 1) low-dose ATG/GCSF or 2) low-dose ATG alone would slow the decline of β-cell function in patients with new-onset T1D (duration <100 days).

RESEARCH DESIGN AND METHODS

A three-arm, randomized, double-masked, placebo-controlled trial was performed by the Type 1 Diabetes TrialNet Study Group in 89 subjects: 29 subjects randomized to ATG (2.5 mg/kg intravenously) followed by pegylated GCSF (6 mg subcutaneously every 2 weeks for 6 doses), 29 to ATG alone (2.5 mg/kg), and 31 to placebo. The primary end point was mean area under the curve (AUC) C-peptide during a 2-h mixed-meal tolerance test 1 year after initiation of therapy. Significance was defined as one-sided P value < 0.025.

RESULTS

The 1-year mean AUC C-peptide was significantly higher in subjects treated with ATG (0.646 nmol/L) versus placebo (0.406 nmol/L) (P = 0.0003) but not in those treated with ATG/GCSF (0.528 nmol/L) versus placebo (P = 0.031). HbA_1c was significantly reduced at 1 year in subjects treated with ATG and ATG/GCSF, P = 0.002 and 0.011, respectively.

CONCLUSIONS

Low-dose ATG slowed decline of C-peptide and reduced HbA_1c in new-onset T1D. Addition of GCSF did not enhance C-peptide preservation afforded by low-dose ATG. Future studies should be considered to determine whether low-dose ATG alone or in combination with other agents may prevent or delay the onset of the disease.

A Type 1 Diabetes Genetic Risk Score Predicts Progression of Islet Autoimmunity and Development of Type 1 Diabetes in Individuals at Risk

OBJECTIVE

We tested the ability of a type 1 diabetes (T1D) genetic risk score (GRS) to predict progression of islet autoimmunity and T1D in at-risk individuals.

RESEARCH DESIGN AND METHODS

We studied the 1,244 TrialNet Pathway to Prevention study participants (T1D patients' relatives without diabetes and with one or more positive autoantibodies) who were genotyped with Illumina ImmunoChip (median [range] age at initial autoantibody determination 11.1 years [1.2-51.8], 48% male, 80.5% non-Hispanic white, median follow-up 5.4 years). Of 291 participants with a single positive autoantibody at screening, 157 converted to multiple autoantibody positivity and 55 developed diabetes. Of 953 participants with multiple positive autoantibodies at screening, 419 developed diabetes. We calculated the T1D GRS from 30 T1D-associated single nucleotide polymorphisms. We used multivariable Cox regression models, time-dependent receiver operating characteristic curves, and area under the curve (AUC) measures to evaluate prognostic utility of T1D GRS, age, sex, Diabetes Prevention Trial-Type 1 (DPT-1) Risk Score, positive autoantibody number or type, HLA DR3/DR4-DQ8 status, and race/ethnicity. We used recursive partitioning analyses to identify cut points in continuous variables.

RESULTS

Higher T1D GRS significantly increased the rate of progression to T1D adjusting for DPT-1 Risk Score, age, number of positive autoantibodies, sex, and ethnicity (hazard ratio [HR] 1.29 for a 0.05 increase, 95% CI 1.06-1.6; P = 0.011). Progression to T1D was best predicted by a combined model with GRS, number of positive autoantibodies, DPT-1 Risk Score, and age (7-year time-integrated AUC = 0.79, 5-year AUC = 0.73). Higher GRS was significantly associated with increased progression rate from single to multiple positive autoantibodies after adjusting for age, autoantibody type, ethnicity, and sex (HR 2.27 for GRS >0.295, 95% CI 1.47-3.51; P = 0.0002).

CONCLUSIONS

The T1D GRS independently predicts progression to T1D and improves prediction along T1D stages in autoantibody-positive relatives.

Hazmat Emergency Preparedness in Hong Kong: What are the Dangerous Goods in Kowloon?

Introduction

Hazmat emergency preparedness is critical, especially as Hong Kong prepares for major international events, such as the 2008 Olympic Equestrian Games. No published medical study has described the identities and quantities of dangerous goods (DG) in the Kowloon area and listed what antidotes are needed for these DG. This study describes what hazardous materials are most common in Kowloon to prioritise emergency preparedness and training.

Materials & methods

Design A descriptive, cross-sectional study. Setting The Hong Kong Special Administrative Region, specifically Kowloon. Sample The Hong Kong Fire Services Department (HKFSD) Dangerous Goods Database (DGD). Interventions Descriptive statistical analyses with Stata 9.2. Chief outcome Identifying and quantifying dangerous goods in the HKFSD DGD.

Results

Most DG do not have antidotes. The most common DG with recognised antidotes are carbon monoxide, methylene chloride, fluorine, fluorides, fluoroboric acid, cyanides, nitriles, methanol, nitrobenzene, nitrites, and nitrates. The most common categories of DG are substances giving off inflammable vapours, compressed gases, and corrosive and poisonous substances.

Conclusions

Hazmat emergency preparedness and training should emphasize these most common categories of DG. Disaster planning should ensure adequate antidotes for DG with recognised antidotes, i.e., oxygen for carbon monoxide and methylene chloride; calcium gluconate or calcium chloride for fluorine, fluorides, and fluoroboric acid; hydroxocobalamin for cyanides and nitriles; ethanol for methanol; and methylene blue for methaemoglobinaemia produced by nitrobenzene, nitrites, and nitrates. Supportive care is essential for patients exposed to hazardous materials because most dangerous goods do not have antidotes.

Abstract P6-15-12: Preclinical Evaluation of a STAT3 Inhibitor in Breast Cancer

Breast cancer often arises from inappropriate activation of transcription factors involved in normal mammary development, such as the signal transducers and activators of transcription (STAT) family of transcription factors. STAT3, which plays an important role in mammary remodeling, is activated (as assessed by tyrosine phosphorylation) in approximately 70% of primary breast cancers, with many of these tumors being highgrade. Furthermore, inhibition of STAT3 leads to a loss of tumorigenicity of breast cancer cells. Therefore, targeting STAT3 in breast cancer would be a potentially beneficial form of therapy.

To identify small molecule STAT3 inhibitors, we developed a high throughput cell-based assay to identify compounds that inhibit STAT3- dependent transcriptional activity. We screened approximately 200,000 compounds, and specificity for STAT3 was ensured by eliminating molecules that inhibited either STAT1- or NF-kappaB-dependent transcriptional activity. From this screen, we identified 4-[4-(phenylmethyl) piperidin-1-yl] thieno[2,3-d]pyrimidine (PMPTP) (Probe ID ML116) as a potent inhibitor of STAT3 transcriptional activity, which has no effect on STAT1 or NF-kappaB-dependent transcriptional activity. Treatment with PMPTP of MDA-MB-468 breast cancer cells, which contain constitutively activated STAT3, leads to inhibition of expression of STAT3 target genes including bcl-x and mcl1. Furthermore, PMPTP is a potent inhibitor of viability of MDA-MB-468 breast cancer cells. By contrast, SK-BR-3 cells, which do not contain constitutively active STAT3, were only minimally affected. This suggests that PMPTP reduces the viability of cells that depend on constitutively active STAT3. PMPTP has no effect on STAT3 tyrosine or serine phosphorylation or STAT3 nuclear translocation, suggesting that PMPTP may be inhibiting STAT3 at the level of DNA binding or co-factor recruitment.

Importantly, PMPTP lowers the apoptotic potential of breast cancer cells thereby making them more susceptible to other forms of therapy. Building on this observation, we identified a number of beneficial combinations of PMPTP with cytotoxic drugs currently used in breast cancer therapy as well as novel anti-cancer agents. Additionally, we analyzed a number of structural analogues of PMPTP, and we identified two compounds that had approximately 4-fold increased potency in inhibiting the viability of breast cancer cells containing STAT3 activation.

Taken together, these findings identify PMPTP as a potential new form of therapy for breast cancers containing activated STAT3, which can be enhanced using conventional and non-conventional chemotherapy.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P6-15-12.

Dynamic micro-Hall detection of superparamagnetic beads in a microfluidic channel

We report integration of an InAs quantum well micro-Hall magnetic sensor with microfluidics and real-time detection of moving superparamagnetic beads. Beads moving within and around the Hall cross area result in positive and negative Hall voltage signals respectively. Relative magnitudes and polarities of the signals measured for a random distribution of immobilized beads over the sensor are in good agreement with calculated values and explain consistently the shape of the dynamic signal.

Contractile properties of muscle fibers from the deep and superficial digital flexors of horses

Equine digital flexor muscles have independent tendons but a nearly identical mechanical relationship to the main joint they act upon. Yet these muscles have remarkable diversity in architecture, ranging from long, unipennate fibers ("short" compartment of DDF) to very short, multipennate fibers (SDF). To investigate the functional relevance of the form of the digital flexor muscles, fiber contractile properties were analyzed in the context of architecture differences and in vivo function during locomotion. Myosin heavy chain (MHC) isoform fiber type was studied, and in vitro motility assays were used to measure actin filament sliding velocity (V(f)). Skinned fiber contractile properties [isometric tension (P(0)/CSA), velocity of unloaded shortening (V(US)), and force-Ca(2+) relationships] at both 10 and 30°C were characterized. Contractile properties were correlated with MHC isoform and their respective V(f). The DDF contained a higher percentage of MHC-2A fibers with myosin (heavy meromyosin) and V(f) that was twofold faster than SDF. At 30°C, P(0)/CSA was higher for DDF (103.5 ± 8.75 mN/mm(2)) than SDF fibers (81.8 ± 7.71 mN/mm(2)). Similarly, V(US) (pCa 5, 30°C) was faster for DDF (2.43 ± 0.53 FL/s) than SDF fibers (1.20 ± 0.22 FL/s). Active isometric tension increased with increasing Ca(2+) concentration, with maximal Ca(2+) activation at pCa 5 at each temperature in fibers from each muscle. In general, the collective properties of DDF and SDF were consistent with fiber MHC isoform composition, muscle architecture, and the respective functional roles of the two muscles in locomotion.

A simple model with myofilament compliance predicts activation-dependent crossbridge kinetics in skinned skeletal fibers

The contribution of thick and thin filaments to skeletal muscle fiber compliance has been shown to be significant. If similar to the compliance of cycling cross-bridges, myofilament compliance could explain the difference in time course of stiffness and force during the rise of tension in a tetanus as well as the difference in Ca(2+) sensitivity of force and stiffness and more rapid phase 2 tension recovery (r) at low Ca(2+) activation. To characterize the contribution of myofilament compliance to sarcomere compliance and isometric force kinetics, the Ca(2+)-activation dependence of sarcomere compliance in single glycerinated rabbit psoas fibers, in the presence of ATP (5.0 mM), was measured using rapid length steps. At steady sarcomere length, the dependence of sarcomere compliance on the level of Ca(2+)-activated force was similar in form to that observed for fibers in rigor where force was varied by changing length. Additionally, the ratio of stiffness/force was elevated at lower force (low [Ca(2+)]) and r was faster, compared with maximum activation. A simple series mechanical model of myofilament and cross-bridge compliance in which only strong cross-bridge binding was activation dependent was used to describe the data. The model fit the data and predicted that the observed activation dependence of r can be explained if myofilament compliance contributes 60-70% of the total fiber compliance, with no requirement that actomyosin kinetics be [Ca(2+)] dependent or that cooperative interactions contribute to strong cross-bridge binding.

Dimethyl sulphoxide enhances the effects of P(i) in myofibrils and inhibits the activity of rabbit skeletal muscle contractile proteins

In the catalytic cycle of skeletal muscle, myosin alternates between strongly and weakly bound cross-bridges, with the latter contributing little to sustained tension. Here we describe the action of DMSO, an organic solvent that appears to increase the population of weakly bound cross-bridges that accumulate after the binding of ATP, but before P(i) release. DMSO (5-30%, v/v) reversibly inhibits tension and ATP hydrolysis in vertebrate skeletal muscle myofibrils, and decreases the speed of unregulated F-actin in an in vitro motility assay with heavy meromyosin. In solution, controls for enzyme activity and intrinsic tryptophan fluorescence of myosin subfragment 1 (S1) in the presence of different cations indicate that structural changes attributable to DMSO are small and reversible, and do not involve unfolding. Since DMSO depresses S1 and acto-S1 MgATPase activities in the same proportions, without altering acto-S1 affinity, the principal DMSO target apparently lies within the catalytic cycle rather than with actin-myosin binding. Inhibition by DMSO in myofibrils is the same in the presence or the absence of Ca(2+) and regulatory proteins, in contrast with the effects of ethylene glycol, and the Ca(2+) sensitivity of isometric tension is slightly decreased by DMSO. The apparent affinity for P(i) is enhanced markedly by DMSO (and to a lesser extent by ethylene glycol) in skinned fibres, suggesting that DMSO stabilizes cross-bridges that have ADP.P(i) or ATP bound to them.

Finding the Underserved: Directions for HIV Care in the Future

The demographic, behavior, and background characteristics of 4,804 participants in 17 national demonstration projects for HIV medical and/or psychosocial support services were coded for an index of "service need" or possible under-representation in the traditional healthcare system. Fifteen items were coded including status as a person of color, lack of private insurance, unemployment/disability, problem drinking, crack cocaine use, heroin use, other illicit drug use, less than 12 years of education, criminal justice system involvement, children requiring care while the patient receives services, sex work, being the sex partner of an injection drug user, unstable housing, primary language not English, and age less than 21 or over 55 years. Most (87.7%) of the program participants had four or more of these factors present. Through CHAID modeling, those groups with the highest levels of service need and vulnerability were identified. These data suggest that these projects, designed to attract and serve individuals potentially underrepresented in the health services system, had in fact achieved that goal. Implications of the changing demographics of the HIV epidemic for the health service delivery system are discussed.

Structural, relative, and absolute agreement between parents' and adolescent inpatients' reports of adolescent functional impairment

This study assessed agreement between parents' and adolescent inpatients' scores on caretaker and self-report versions of the Functional Impairment Scale for Children and Adolescents (FISCA and FISCA-SR). Self-report data describing impairment in eight domains were collected from 375 inpatients (M age = 15.0 years, 55% females), with parent data available for 233 (62%). Confirmatory factor analysis demonstrated structural congruence between a hypothesized, three-factor model, based on a prior study of the parent FISCA, and an observed model, based on responses to the FISCA-SR (GFI = .95). Correlations (measuring relative agreement) and paired comparisons of means (assessing absolute agreement) generally identified stronger agreement in "public" than "private" domains of impairment, and greater relative than absolute agreement in covert, antisocial domains.

2-deoxy-ATP enhances contractility of rat cardiac muscle

To investigate the kinetic parameters of the crossbridge cycle that regulate force and shortening in cardiac muscle, we compared the mechanical properties of cardiac trabeculae with either ATP or 2-deoxy-ATP (dATP) as the substrate for contraction. Comparisons were made in trabeculae from untreated rats (predominantly V1 myosin) and those treated with propylthiouracil (PTU; V3 myosin). Steady-state hydrolytic activity of cardiac heavy meromyosin (HMM) showed that PTU treatment resulted in >40% reduction of ATPase activity. dATPase activity was >50% elevated above ATPase activity in HMM from both untreated and PTU-treated rats. V(max) of actin-activated hydrolytic activity was also >50% greater with dATP, whereas the K(m) for dATP was similar to that for ATP. This indicates that dATP increased the rate of crossbridge cycling in cardiac muscle. Increases in hydrolytic activity were paralleled by increases of 30% to 80% in isometric force (F(max)), rate of tension redevelopment (k(tr)), and unloaded shortening velocity (V(u)) in trabeculae from both untreated and PTU-treated rats (at maximal Ca(2+) activation), and F-actin sliding speed in an in vitro motility assay (V(f)). These results contrast with the effect of dATP in rabbit psoas and soleus fibers, where F(max) is unchanged even though k(tr), V(u), and V(f) are increased. The substantial enhancement of mechanical performance with dATP in cardiac muscle suggests that it may be a better substrate for contractility than ATP and warrants exploration of ribonucleotide reductase as a target for therapy in heart failure.

Viscosity and solute dependence of F-actin translocation by rabbit skeletal heavy meromyosin

We tested the hypothesis that solvent viscosity affects translocation of rhodamine phalloidin-labeled F-actin by rabbit skeletal heavy meromyosin (HMM). When viscosity was increased using either glycerol, fructose, sucrose, or dextran (1.5, 6.0, or 15-20 kDa mol mass), there was little or no effect on the fraction of moving filaments, whereas sliding speed decreased in inverse proportion to viscosity. The results could be explained neither by an effect of osmotic pressure at high solute concentrations nor by altered solvent drag on the actin filament. Elevated viscosity inhibited HMM ATPase activity in solution, but only at much higher viscosities than were needed to reduce sliding speed. Polyethylene glycols (300, 1,000, or 3,000 mol wt) also inhibited speed via elevated viscosity but secondarily inhibited by enhancing electrostatic interactions. These results demonstrate that a diffusion-controlled process intrinsic to cross-bridge cycling can be limiting to actomyosin function.

The psychiatric consultation/liaison nurse role in case management

Psychiatric consultation/liaison nurses focus on the emotional, spiritual, developmental, cognitive, and behavioral responses of patients and families. They help patients, family, staff, and the entire healthcare system cope with a medical illness and its treatment. Use of psychiatric consultation/liaison nurses ensures that the patient's emotional needs are met, patients and families feel more cared for and respected, and patient satisfaction is increased. Partnerships between case managers and psychiatric consultation/liaison nurses may be especially effective with complex cases, end-of-life decisions, unanticipated hospital stays, certain pediatric populations, and patients who are hospitalized far from home. This article includes four case studies to illustrate such partnerships in a large teaching hospital.

In the steps of giants: the early geriatrics texts

This article briefly reviews some of the major early geriatric textbooks of the last two centuries. Among the more important are books by George Day, Charcot, Nascher, Worcester, and Cowdry. Lord Amulree's book Adding Life to Years has become a watchword of modern geriatrics. It is of interest that during this time period the basic plea for high touch care of older patients and the lament that physicians have little knowledge of the needs of older patients has remained remarkably constant.

Pancreatitis Partners: a sharing and educational support group

A team in a digestive disease center at a 550-bed tertiary care center in the Southeast created an interactive, educational patient and family support group for people with pancreatitis. No previous support groups for this population could be located in the United States by us, although pancreatitis is a disease that may progress to include chronic pain, frequent hospitalizations or emergency room visits, narcotic dependence, and depression. The article describes and illustrates the need, planning, inception, implementation, evaluation, and re-visioning of an outpatient support and education group for people affected by pancreatitis. The group uses a partnership model as a basis for helping empower patients and their family members to have more understanding of, adaption to, and say in the treatment choices and responsibility for managing symptoms of their chronic illness. Facilitated by a multidisciplinary team, this is the first group of its kind in the United States and was enthusiastically received by those who participated. Group members were surveyed at the conclusion of the first ten group sessions. Results of this survey and modification to the group format and expanded outreach plans to people affected by pancreatitis are outlined and discussed.

Contractile properties of rabbit psoas muscle fibres inhibited by beryllium fluoride

The structure of truncated, recombinant Dictyostelium myosin motor domain complexed with Mg.ADP and slowly dissociating analogues of Pi has previously been characterized as two main states (S1-MgADP plus BeFx vs. A1F4- or Vi). The BeFx bound state is thought to mimic the weak actin-binding M.ATP complex, while the states with A1F4- or Vi bound mimic the M.ADP.Pi state. While the effects of A1F4- and Vi on fibre mechanics have been previously described (Chase et al., 1994, 1993), the effects of BeFx have not been characterized in detail. At pCa 4.5 (12 degrees C), we measured (i) steady-state isometric tension, (ii) stiffness (KS; 1 kHz sinusoids), and (iii) unloaded shortening velocity (Vu; slack test) in single skinned muscle fibres from rabbit psoas. Results were compared when tension was inhibited with either BeFx or 2,3-butanedione-monoxime (BDM) or modulated by altering myoplasmic [Ca2+]. With 3 mM total fluoride, 1 mM BeFx inhibited both tension and KS by approximately 50% (compared to 7-10 mM BDM and 50-100 microM A1F4-). Increasing [BeFx] to 10 mM further reduced tension to approximately 15% P0, but had little further effect on KS; with BDM and altered [Ca2+], KS scaled more proportionately with tension. Inhibition of tension and KS by BeFx was more rapidly reversible, compared with slow recovery from tension inhibition with A1F4- or Vi. Vu exhibited a complex dependence on [BeFx], being relatively unaffected by concentrations < or = 1 mM, and becoming inhibited steeply for [BeFx] above this level. With BDM, Vu co-varied more directly with force. Our results suggest that BeFx may induce a different cross-bridge state in fibres than do A1F4- or Vi, but all three analogues of Pi form complexes that mimic crossbridge states that follow ATP hydrolysis.

Regulation of skeletal muscle tension redevelopment by troponin C constructs with different Ca2+ affinities

In maximally activated skinned fibers, the rate of tension redevelopment (ktr) following a rapid release and restretch is determined by the maximal rate of cross-bridge cycling. During submaximal Ca2+ activations, however, ktr regulation varies with thin filament dynamics. Thus, decreasing the rate of Ca2+ dissociation from TnC produces a higher ktr value at a given tension level (P), especially in the [Ca2+] range that yields less than 50% of maximal tension (Po). In this study, native rabbit TnC was replaced with chicken recombinant TnC, either wild-type (rTnC) or mutant (NHdel), with decreased Ca2+ affinity and an increased Ca2+ dissociation rate (koff). Despite marked differences in Ca2+ sensitivity (>0.5 DeltapCa50), fibers reconstituted with either of the recombinant proteins exhibited similar ktr versus tension profiles, with ktr low (1-2 s-1) and constant up to approximately 50% Po, then rising sharply to a maximum (16 +/- 0.8 s-1) in fully activated fibers. This behavior is predicted by a four-state model based on coupling between cross-bridge cycling and thin filament regulation, where Ca2+ directly affects only individual thin filament regulatory units. These data and model simulations confirm that the range of ktr values obtained with varying Ca2+ can be regulated by a rate-limiting thin filament process.

Ca2+ and cross-bridge-induced changes in troponin C in skinned skeletal muscle fibers: effects of force inhibition

Changes in skeletal troponin C (sTnC) structure during thin filament activation by Ca2+ and strongly bound cross-bridge states were monitored by measuring the linear dichroism of the 5' isomer of iodoacetamidotetramethylrhodamine (5'IATR), attached to Cys98 (sTnC-5'ATR), in sTnC-5'ATR reconstituted single skinned fibers from rabbit psoas muscle. To isolate the effects of Ca2+ and cross-bridge binding on sTnC structure, maximum Ca2+-activated force was inhibited with 0.5 mM AlF4- or with 30 mM 2,3 butanedione-monoxime (BDM) during measurements of the Ca2+ dependence of force and dichroism. Dichroism was 0.08 +/- 0.01 (+/- SEM, n = 9) in relaxing solution (pCa 9.2) and decreased to 0.004 +/- 0.002 (+/- SEM, n = 9) at pCa 4.0. Force and dichroism had similar Ca2+ sensitivities. Force inhibition with BDM caused no change in the amplitude and Ca2+ sensitivity of dichroism. Similarly, inhibition of force at pCa 4.0 with 0.5 mM AlF4- decreased force to 0.04 +/- 0.01 of maximum (+/- SEM, n = 3), and dichroism was 0.04 +/- 0.03 (+/- SEM, n = 3) of the value at pCa 9.2 and unchanged relative to the corresponding normalized value at pCa 4.0 (0.11 +/- 0.05, +/- SEM; n = 3). Inhibition of force with AlF4- also had no effect when sTnC structure was monitored by labeling with either 5-dimethylamino-1-napthalenylsulfonylaziridine (DANZ) or 4-(N-(iodoacetoxy)ethyl-N-methyl)amino-7-nitrobenz-2-oxa-1,3-diazole (NBD). Increasing sarcomere length from 2.5 to 3.6 microm caused force (pCa 4.0) to decrease, but had no effect on dichroism. In contrast, rigor cross-bridge attachment caused dichroism at pCa 9.2 to decrease to 0.56 +/- 0.03 (+/- SEM, n = 5) of the value at pCa 9. 2, and force was 0.51 +/- 0.04 (+/- SEM, n = 6) of pCa 4.0 control. At pCa 4.0 in rigor, dichroism decreased further to 0.19 +/- 0.03 (+/- SEM, n = 6), slightly above the pCa 4.0 control level; force was 0.66 +/- 0.04 of pCa 4.0 control. These results indicate that cross-bridge binding in the rigor state alters sTnC structure, whereas cycling cross-bridges have little influence at either submaximum or maximum activating [Ca2+].

Skeletal muscle regulatory proteins enhance F-actin in vitro motility

Using an in vitro motility assay, we have investigated the effects of rabbit skeletal muscle regulatory proteins, troponin and tropomyosin, on the gliding of F-actin filaments or F-actin filaments containing these regulatory proteins. We demonstrate that Ca2+ does not affect the motility of F-actin gliding on HMM, but does in the presence of skeletal muscle tropomyosin and troponin. We conclude that Ca2+ affects motility through troponin because, like F-actin, F-actin-Tm filaments show no Ca(2+)-dependence to their gliding speeds. Furthermore, there is a large enhancement of the gliding speed (about 75%) in the presence of skeletal muscle tropomyosin, troponin + saturating Ca2+ over that seen with F-actin filaments. This enhancement is not due to the action of tropomyosin alone as skeletal muscle tropomyosin without troponin enhances the speed little (about 5%) over that of F-actin. Thus troponin confers Ca2+ sensitivity to the motility and, additionally, potentiates motility greatly along with tropomyosin in the presence of saturating Ca2+. When [HMM] is varied, the decline in speed of F-actin seen at low HMM density is changed little by tropomyosin in the F-actin-Tm filaments. These data show that the skeletal regulatory proteins interact with F-actin to enhance the interaction with HMM particularly in the presence of troponin and saturating Ca2+ and enhance the gliding speed in the in vitro motility assay as they potentiate the ATPase activity in the isolated proteins. This enhancement of speed in the motility assay cannot be ascribed to tropomyosin alone.

Compliant realignment of binding sites in muscle: transient behavior and mechanical tuning

The presence of compliance in the lattice of filaments in muscle raises a number of concerns about how one accounts for force generation in the context of the cross-bridge cycle--binding site motions and coupling between cross-bridges confound more traditional analyses. To explore these issues, we developed a spatially explicit, mechanochemical model of skeletal muscle contraction. With a simple three-state model of the cross-bridge cycle, we used a Monte Carlo simulation to compute the instantaneous balance of forces throughout the filament lattice, accounting for both thin and thick filament distortions in response to cross-bridge forces. This approach is compared to more traditional mass action kinetic models (in the form of coupled partial differential equations) that assume filament inextensibility. We also monitored instantaneous force generation, ATP utilization, and the dynamics of the cross-bridge cycle in simulations of step changes in length and variations in shortening velocity. Three critical results emerge from our analyses: 1) there is a significant realignment of actin-binding sites in response to cross-bridge forces, 2) this realignment recruits additional cross-bridge binding, and 3) we predict mechanical behaviors that are consistent with experimental results for velocity and length transients. Binding site realignment depends on the relative compliance of the filament lattice and cross-bridges, and within the measured range of these parameters, gives rise to a sharply tuned peak for force generation. Such mechanical tuning at the molecular level is the result of mechanical coupling between individual cross-bridges, mediated by thick filament deformations, and the resultant realignment of binding sites on the thin filament.

Calcium regulation of tension redevelopment kinetics with 2-deoxy-ATP or low [ATP] in rabbit skeletal muscle

The correlation of acto-myosin ATPase rate with tension redevelopment kinetics (k(tr)) was determined during Ca(+2)-activated contractions of demembranated rabbit psoas muscle fibers; the ATPase rate was either increased or decreased relative to control by substitution of ATP (5.0 mM) with 2-deoxy-ATP (dATP) (5.0 mM) or by lowering [ATP] to 0.5 mM, respectively. The activation dependence of k(tr) and unloaded shortening velocity (Vu) was measured with each substrate. With 5.0 mM ATP, Vu depended linearly on tension (P), whereas k(tr) exhibited a nonlinear dependence on P, being relatively independent of P at submaximum levels and rising steeply at P > 0.6-0.7 of maximum tension (Po). With dATP, Vu was 25% greater than control at Po and was elevated at all P > 0.15Po, whereas Po was unchanged. Furthermore, the Ca(+2) sensitivity of both k(tr) and P increased, such that the dependence of k(tr) on P was not significantly different from control, despite an elevation of Vu and maximal k(tr). In contrast, lowering [ATP] caused a slight (8%) elevation of Po, no change in the Ca(+2) sensitivity of P, and a decrease in Vu at all P. Moreover, k(tr) was decreased relative to control at P > 0.75Po, but was elevated at P < 0.75Po. These data demonstrate that the cross-bridge cycling rate dominates k(tr) at maximum but not submaximum levels of Ca(2+) activation.

Effect of viscosity on mechanics of single, skinned fibers from rabbit psoas muscle

Muscle contraction is highly dynamic and thus may be influenced by viscosity of the medium surrounding the myofilaments. Single, skinned fibers from rabbit psoas muscle were used to test this hypothesis. Viscosity within the myofilament lattice was increased by adding to solutions low molecular weight sugars (disaccharides sucrose or maltose or monosaccharides glucose or fructose). At maximal Ca2+ activation, isometric force (Fi) was inhibited at the highest solute concentrations studied, but this inhibition was not directly related to viscosity. Solutes readily permeated the filament lattice, as fiber diameter was unaffected by added solutes (except for an increased diameter with Fi < 30% of control). In contrast, there was a linear dependence upon 1/viscosity for both unloaded shortening velocity and also the kinetics of isometric tension redevelopment; these effects were unrelated to either variation in solution osmolarity or inhibition of force. All effects of added solute were reversible. Inhibition of both isometric as well as isotonic kinetics demonstrates that viscous resistance to filament sliding was not the predominant factor affected by viscosity. This was corroborated by measurements in relaxed fibers, which showed no significant change in the strain-rate dependence of elastic modulus when viscosity was increased more than twofold. Our results implicate cross-bridge diffusion as a significant limiting factor in cross-bridge kinetics and, more generally, demonstrate that viscosity is a useful probe of actomyosin dynamics.

Evidence for platelet-activating factor receptor subtypes on human polymorphonuclear leukocyte membranes

Platelet-activating factor (PAF) is a potent phospholipid mediator that acts through specific cell surface receptors. The existence of PAF receptor subtypes has been suggested by functional and radioligand binding studies in a variety of cells and tissues. This report addresses this issue more directly and demonstrates differences between specific PAF receptors in human polymorphonuclear leukocytes (PMNs) and COS-7 cells transfected with the cloned human PAF receptor gene. The presence of more than one receptor in human PMNs is supported by three different studies. First, the Kd from the saturation isotherms for the binding of [3H]WEB 2086 on PMNs was 7-fold larger (Kd = 29.2 nM) than the kinetic Kd (4.2 nM). Second, the pseudo-Hill slope determined from the saturation experiments with PMNs was significantly lower than unity (0.69 +/- 0.05 SEM), and the saturation Kd values for transfected COS-7 (Kd = 9.6 nM) and PMN membranes were significantly different. These results contrasted with those for the transfected COS-7 cells, which showed a Kd from the saturation isotherms similar to that of the kinetic Kd (3.2 nM) and a pseudo-Hill slope that was not different from 1.0. Third, when the radiolabeled ligand [3H]WEB 2086 was increased in concentration from 10 to 50 nM in inhibition experiments with the human PMN membranes, the Ki increased, indicative of binding mainly to receptors with lower affinity. These results suggest that PAF receptor subtypes exist in human PMNs based on distinct radioligand binding characteristics from the human cloned PAF receptor.

Collection and recruitment of CD34+ cells during large-volume leukapheresis

Although sufficient progenitor cells for hematopoietic rescue following high-dose therapy may be obtained in a single leukapheresis, the majority of patients require multiple procedures. In an attempt to minimize the number of leukapheresis and maximize collection efficiency, we undertook large-volume leukapheresis in 17 patients with a variety of hematologic malignancies. Twenty-four procedures were performed over a 6-h period, with a mean of 21 L of blood processed. By employing a modified collection set, three separate 2-h collection bags were analyzed for a number of variables. CD34+ cells are collected at a steady rate throughout the procedure, with no evidence of exhaustion of progenitor cells. There was evidence of progenitor cell recruitment, with 1.4-fold more CD34+ cells in the collected product than were present in the blood at the beginning of the procedure. Initiation of leukapheresis was based on the blood CD34+ count, and this value was strongly correlated with the number of CD34+ cells in the collected product. The procedure is safe and relatively simple and minimizes the number of leukaphereses required to collect adequate progenitors for autologous transplantation.

Calcium regulation of skeletal muscle thin filament motility in vitro

Using an in vitro motility assay, we have investigated Ca2+ regulation of individual, regulated thin filaments reconstituted from rabbit fast skeletal actin, troponin, and tropomyosin. Rhodamine-phalloidin labeling was used to visualize the filaments by epifluorescence, and assays were conducted at 30 degrees C and at ionic strengths near the physiological range. Regulated thin filaments exhibited well-regulated behavior when tropomyosin and troponin were added to the motility solutions because there was no directed motion in the absence of Ca2+. Unlike F-actin, the speed increased in a graded manner with increasing [Ca2+], whereas the number of regulated thin filaments moving was more steeply regulated. With increased ionic strength, Ca2+ sensitivity of both the number of filaments moving and their speed was shifted toward higher [Ca2+] and was steepest at the highest ionic strength studied (0.14 M gamma/2). Methylcellulose concentration (0.4% versus 0.7%) had no effect on the Ca2+ dependence of speed or number of filaments moving. These conclusions hold for five different methods used to analyze the data, indicating that the conclusions are robust. The force-pCa relationship (pCa = -log10[Ca2+]) for rabbit psoas skinned fibers taken under similar conditions of temperature and solution composition (0.14 M gamma/2) paralleled the speed-pCa relationship for the regulated filaments in the in vitro motility assay. Comparison of motility results with the force-pCa relationship in fibers suggests that relatively few cross-bridges are needed to make filaments move, but many have to be cycling to make the regulated filament move at maximum speed.

Antiislet autoantibodies usually develop sequentially rather than simultaneously

The goal of this study was to address whether antiislet autoantibodies appear sequentially or simultaneously before the onset of type I diabetes. We analyzed sequential serum samples from 155 siblings and offspring (aged < 7 yr) of patients with type I diabetes from the Denver Diabetes Autoimmunity Study in the Young study and from a separate group of first degree relatives (aged 2-40 yr) for autoantibodies reacting with three defined autoantigens: glutamic acid decarboxylase (GAD65), insulin, and ICA512/IA-2. The youngest age at which 1 of the 3 autoantibodies appeared was 1.1 yr, and the oldest was 60.9 yr. Of the total 26 autoantibody conversion events observed, in only 3 instances did more than 1 autoantibody appear simultaneously. Among individuals (n = 12) with sequential conversion to expression of multiple autoantibodies, anti-GAD65 autoantibodies or antiinsulin autoantibodies appeared first (4 expressed antiinsulin autoantibodies first, and 8 anti-GAD65 autoantibodies first). We conclude that antiislet autoantibodies usually appear sequentially and not simultaneously. This corroborates early suggestions that humoral autoimmunity to islets develops chronically in a process usually measured in months to years. As expression of multiple autoantibodies is associated with a high risk of progression to diabetes, and sequential appearance of autoantibodies can occur late in life, long term follow-up is necessary to fully delineate the relationship of diabetes risk to autoantibody expression.

Calmidazolium alters Ca2+ regulation of tension redevelopment rate in skinned skeletal muscle

To examine if the Ca2(+)-binding kinetics of troponin C (TnC) can influence the rate of cross-bridge force production, we studied the effects of calmidazolium (CDZ) on steady-state force and the rate of force redevelopment (ktr) in skinned rabbit psoas muscle fibers. CDZ increased the Ca2(+)-sensitivity of steady-state force and ktr at submaximal levels of activation, but increased ktr to a greater extent than can be explained by increased force alone. This occurred in the absence of any significant effects of CDZ on solution ATPase or in vitro motility of fluorescently labeled F-actin, suggesting that CDZ did not directly influence cross-bridge cycling. CDZ was strongly bound to TnC in aqueous solutions, and its effects on force production could be reversed by extraction of CDZ-exposed native TnC and replacement with purified (unexposed) rabbit skeletal TnC. These experiments suggest that the method of CDZ action in fibers is to bind to TnC and increase its Ca2(+)-binding affinity, which results in an increased rate of force production at submaximal [Ca2+]. The results also demonstrate that the Ca2(+)-binding kinetics of TnC influence the kinetics of ktr.

Effect of intracellular pH on force development depends on temperature in intact skeletal muscle from mouse

The cellular mechanism of muscle fatigue is still in debate. Opposite conclusions regarding the role of intracellular pH (pHi) in fatigue have been drawn from skinned fiber vs. isolated perfused muscle studies. Because these experiments are typically performed at different temperatures, we tested the hypothesis that temperature alters the effects of pH on force. Tetanic force of isolated mouse extensor digitorum longus was measured at temperatures between 13 and 25 degrees C in either normocapnia (5% CO2) or hypercapnia (25% CO2). Hypercapnia decreased pHi (monitored by 31P nuclear magnetic resonance spectroscopy) by the same amount at both 15 and 25 degrees C. However, inhibition of force by hypercapnia was greater at the lower temperature. A similar pattern of temperature-dependent inhibition of force by pH was observed in glycerinated fibers from rabbit psoas at maximum Ca2+ activation. We conclude that temperature differences are responsible for disparate conclusions on the role of pHi in muscle fatigue. Based on our results, we suggest that changes in pHi may have little or no role in the loss in force production associated with muscular fatigue at physiological temperatures.

Regional mapping of the human platelet-activating factor receptor gene (PTAFR) to 1p35-->p34.3 by fluorescence in situ hybridization

The human platelet-activating factor cell-surface receptor (PTAFR) is a G protein-coupled receptor thought to contribute to many atopic and inflammatory diseases and, perhaps, to the growth of some neoplasms. Exploring the possibility that the PTAFR might be involved in the genetic predisposition to any disease requires knowledge of its chromosomal localization. In this paper we have used a 20-kb human genomic fragment containing the coding sequence of the cloned PTAFR to determine the regional chromosomal localization of the gene. Using fluorescence in situ hybridization, the localization of the human PTAFR gene was mapped to 1p35-->p34.3.

Rumor management in nursing systems: role of the psychiatric CNS

RUMOR MANAGEMENT AND control is particularly important in nursing systems during times of change. In this article, a brief history of the study of rumor and the rumor process is given and applied to nursing, systems thinking and the CNS, and three types of rumor are described. Examples are given and strategies and approaches for managing rumor are prescribed. The first approach, used when a final decision about a planned change has not been made, helps avoid "trickle down" and builds trust and empowerment by soliciting and using input from those who will be affected by the proposed change. The intent of the second approach, used when a decision has been finalized or an event has occurred and rumor has preceded an official announcement, is to debrief from the occurrence or transform the decision. The last approach is used to interrupt a pattern of misinformation and to clarify or inform. The nurse leader or manager must stay in the communication loop and refrain from blaming a speculated source in order to correct information.

Effect of physiological ADP concentrations on contraction of single skinned fibers from rabbit fast and slow muscles

To directly assess the possible role of ADP in muscle fatigue, we have studied the effect of physiological MgADP levels on maximum Ca(2+)-activated isometric force and unloaded shortening velocity (Vus) of single skinned fiber segments from rabbit fast-twitch (psoas) and slow-twitch (soleus) muscles. MgADP concentration was changed in a controlled and well-buffered manner by varying creatine (Cr) in solutions, which also contained MgATP, phosphocreatine (PCr), and creatine kinase (CK). To quantify ADP as a function of Cr added, we determined the apparent equilibrium constant (K') of CK for the conditions of our experiments (pH 7.1, 3 mM Mg2+, 12 degrees C): K' = (sigma [Cr]. sigma [ATP])/(sigma [PCr]. sigma [ADP]) = 260 +/- 3 (SE). In this manner, ADP was altered essentially as occurs during stimulation in vivo but without the concomitant changes in pH and P(i), which affect force and Vus. As ADP (and Cr) was increased, force and Vus decreased in both fiber types; at the highest ADP level used, 200 microM, normalized force was 96.6 +/- 1.7% for psoas (n = 6) and 93.7 +/- 2.8% for soleus (n = 6), and Vus was 80.4 +/- 2.4% for psoas and 91.3 +/- 7.7% for soleus. Diffusion-reaction calculations indicated that radial gradients of metabolite concentrations within fibers could not explain the small effects of ADP on fiber mechanics, and experiments verified that metabolite levels were well buffered within fibers by the CK reaction. Exogenous CK was added to bathing solutions at 290 U/ml, threefold above that necessary to maintain Vus independent of CK concentration; in the absence of PCr and exogenous CK, at least a fourfold increased MgATP was necessary to maintain Vus at the control level. Adenylate kinase activity was not detectable; thus myofibrillar adenosine-triphosphatase and exogenous CK activities were the major determinants of nucleotide levels within activated cells. Cr alone (in absence of PCr and exogenous CK) also decreased force and Vus, presumably by a nonspecific mechanism. Over the physiological range, altered ADP had little or no effect on force or Vus in well-buffered conditions. It is therefore likely that other factors decrease force and Vus during muscular fatigue.

Faster force transient kinetics at submaximal Ca2+ activation of skinned psoas fibers from rabbit

The early, rapid phase of tension recovery (phase 2) after a step change in sarcomere length is thought to reflect the force-generating transition of myosin bound to actin. We have measured the relation between the rate of tension redevelopment during phase 2 (r), estimated from the half-time of tension recovery during phase 2 (r = t0.5(-1)), and steady-state force at varying [Ca2+] in single fibers from rabbit psoas. Sarcomere length was monitored continuously by laser diffraction of fiber segments (length approximately 1.6 mm), and sarcomere homogeneity was maintained using periodic length release/restretch cycles at 13-15 degrees C. At lower [Ca2+] and forces, r was elevated relative to that at pCa 4.0 for both releases and stretches (between +/- 8 nm). For releases of -3.4 +/- 0.7 nm.hs-1 at pCa 6.6 (where force was 10-20% of maximum force at pCa 4.0), r was 3.3 +/- 1.0 ms-1 (mean +/- SD; N = 5), whereas the corresponding value of r at pCa 4.0 was 1.0 +/- 0.2 ms-1 for releases of -3.5 +/- 0.5 nm.hs-1 (mean +/- SD; N = 5). For stretches of 1.9 +/- 0.7 nm.hs-1, r was 1.0 +/- 0.3 ms-1 (mean +/- SD; N = 9) at pCa 6.6, whereas r was 0.4 +/- 0.1 ms-1 at pCa 4.0 for stretches of 1.9 +/- 0.5 (mean +/- SD; N = 14). Faster phase 2 transients at submaximal Ca(2+)-activation were not caused by changes in myofilament lattice spacing because 4% Dextran T-500, which minimizes lattice spacing changes, was present in all solutions. The inverse relationship between phase 2 kinetics and force obtained during steady-state activation of skinned fibers appears to be qualitatively similar to observations on intact frog skeletal fibers during the development of tetanic force. The data are consistent with models that incorporate a direct effect of [Ca2+] on phase 2 kinetics of individual cross-bridges or, alternatively, in which phase 2 kinetics depend on cooperative interactions between cross-bridges.

Isometric force redevelopment of skinned muscle fibers from rabbit activated with and without Ca2+

Fiber isometric tension redevelopment rate (kTR) was measured during submaximal and maximal activations in glycerinated fibers from rabbit psoas muscle. In fibers either containing endogenous skeletal troponin C (sTnC) or reconstituted with either purified cardiac troponin C (cTnC) or sTnC, graded activation was achieved by varying [Ca2+]. Some fibers were first partially, then fully, reconstituted with a modified form of cTnC (aTnC) that enables active force generation and shortening in the absence of Ca2+. kTR was derived from the half-time of tension redevelopment. In control fibers with endogenous sTnC, kTR increased nonlinearly with [Ca2+], and maximal kTR was 15.3 +/- 3.6 s-1 (mean +/- SD; n = 26 determinations on 25 fibers) at pCa 4.0. During submaximal activations by Ca2+, kTR in cTnC reconstituted fibers was approximately threefold faster than control, despite the lower (60%) maximum Ca(2+)-activated force after reconstitution. To obtain submaximal force with aTnC, eight fibers were treated to fully extract endogenous sTnC, then reconstituted with a mixture of a TnC and cTnC (aTnC:cTnC molar ratio 1:8.5). A second extraction selectively removed cTnC. In such fibers containing aTnC only, neither force nor kTR was affected by changes in [Ca2+]. Force was 22 +/- 7% of maximum control (mean +/- SD; n = 15) at pCa 9.2 vs. 24 +/- 8% (mean +/- SD; n = 8) at pCa 4.0, whereas kTR was 98 +/- 14% of maximum control (mean +/- SD; n = 15) at pCa 9.2 vs. 96 +/- 15% (mean +/- SD; n = 8) at pCa 4.0. Maximal reconstitution of fibers with aTnC alone increased force at pCa 9.2 to 69 +/- 5% of maximum control (mean + SD; n = 22 determinations on 13 fibers) and caused a small but significant reduction of kTR to 78 +/- 8% of maximum control (mean +/- SD; n = 22 determinations on 13 fibers); neither force nor krR was significantly affected by Ca>2(pCa 4.0). Taken together, we interpret our results to indicate that kTR reflects the dynamics of activation of individual thin filament regulatory units and that modulation of kTR by Ca> is effected primarily by Ca>+ binding to TnC.

Unloaded shortening of skinned muscle fibers from rabbit activated with and without Ca2+

Unloaded shortening velocity (VUS) was determined by the slack method and measured at both maximal and submaximal levels of activation in glycerinated fibers from rabbit psoas muscle. Graded activation was achieved by two methods. First, [Ca2+] was varied in fibers with endogenous skeletal troponin C (sTnC) and after replacement of endogenous TnC with either purified cardiac troponin C (cTnC) or sTnC. Alternatively, fibers were either partially or fully reconstituted with a modified form of cTnC (aTnC) that enables force generation and shortening in the absence of Ca2+. Uniformity of the distribution of reconstituted TnC across the fiber radius was evaluated using fluorescently labeled sTnC and laser scanning fluorescence confocal microscopy. Fiber shortening was nonlinear under all conditions tested and was characterized by an early rapid phase (VE) followed by a slower late phase (VL). In fibers with endogenous sTnC, both VE and VL varied with [Ca2+], but VE was less affected than VL. Similar results were obtained after extraction of TnC and reconstitution with either sTnC or cTnC, except for a small increase in the apparent activation dependence of VE. Partial activation with aTnC was obtained by fully extracting endogenous sTnC followed by reconstitution with a mixture of aTnC and cTnC (aTnC:cTnC molar ratio 1:8.5). At pCa 9.2, VE and VL were similar to those obtained in fibers reconstituted with sTnC or cTnC at equivalent force levels. In these fibers, which contained aTnC and cTnC, VE and VL increased with isometric force when [Ca2+] was increased from pCa 9.2 to 4.0. Fibers that contained a mixture of a TnC and cTnC were then extracted a second time to selectively remove cTnC. In fibers containing aTnC only, VE and VL were proportional to the resulting submaximal isometric force compared with maximum Ca(2+)-activated control. With aTnC alone, force, VE, and VL were not affected by changes in [Ca2+]. The similarity of activation dependence of VUS whether fibers were activated in a Ca(2+)-sensitive or -insensitive manners implies that VUS is determined by the average level of thin filament activation and that, with sTnC or cTnC, VUS is affected by Ca2+ binding to TnC only.

Remission and relapse of substance use disorders in schizophrenia. Results from a one-year prospective study

Recent studies of the effectiveness of specialized programs that treat substance use disorders in schizophrenia have obtained promising results but have not involved control groups. Interpretation of these apparently positive results is problematic because remission and relapse rates of substance use disorders have not been reported in this population. The present study reports 1-year rates of substance abuse and dependence remission and relapse in a sample of schizophrenics taken from the Epidemiologic Catchment Area study. Results indicated that the prevalence of substance use disorders in schizophrenia remained constant over the year primarily because rates of remission were balanced by rates of relapse. Individuals who developed abuse or dependence over the year were younger, male, and showed increases in depression and risk for hospitalization over the year. Individuals who remitted abuse or dependence were older, female, and showed decreases in depression over the year. Dual diagnosis treatment programs have recently reported higher rates of remission than were evidenced in this sample, thus providing preliminary support for the effectiveness of these treatments.

Activation dependence and kinetics of force and stiffness inhibition by aluminiofluoride, a slowly dissociating analogue of inorganic phosphate, in chemically skinned fibres from rabbit psoas muscle

To examine the mechanism by which aluminiofluoride, a tightly binding analogue of inorganic phosphate, inhibits force in single, chemically skinned fibres from rabbit psoas muscle, we measured the Ca(2+)-dependence of the kinetics of inhibitor dissociation and the kinetics of actomyosin interactions when aluminiofluoride was bound to the crossbridges. The relation between stiffness and the speed of stretch during small amplitude ramp stretches (< 5 nm per h.s.) was used to characterize the kinetic properties of crossbridges attached to actin; sarcomere length was assessed with HeNe laser diffraction. During maximum Ca(2+)-activation at physiological ionic strength (pCa 4.0, 0.2 M gamma/2), stiffness exhibited a steep dependence on the rate of stretch; aluminiofluoride inhibition at pCa 4.0 (0.2 M gamma/2) resulted in an overall decrease in stiffness, with stiffness at high rates of stretch (10(3)-10(4) nm per h.s. per s) being disproportionately reduced. Thus the slope of the stiffness-speed relation was reduced during aluminiofluoride inhibition of activated fibres. Relaxation of inhibited fibres (pCa 9.2, 0.2 M gamma/2) resulted in aluminiofluoride being 'trapped' and was accompanied by a further decrease in stiffness at all rates of stretch which was comparable to that found in control relaxed fibres. In relaxed, low ionic strength conditions (pCa 9.2, 0.02 M gamma/2) which promote weak crossbridge binding, stiffness at all rates of stretch was significantly inhibited by aluminiofluoride 'trapped' in the fibre. To determine the Ca(2+)-dependence of inhibitor dissociation, force was regulated independent of Ca2+ using an activating troponin C (aTnC). Results obtained with a TnC-activated fibres confirmed that there is no absolute requirement for Ca2+ for recovery from force inhibition by inorganic phosphate analogues in skinned fibres; the only requirement is thin filament activation which enables active crossbridge cycling. These results indicate that aluminiofluoride preferentially inhibits rapid equilibrium or weak crossbridge attachment to actin, that aluminiofluoride-bound crossbridges attach tightly to the activated thin filament, and that, at maximal (or near-maximal) activation, crossbridge attachment to actin prior to inorganic phosphate analogue dissociation is the primary event regulated by Ca2+.

Advanced human resources planning

Programs developed to advance the careers of pharmacy staff members are important tools to attract and retain qualified staff members. Integration of career development with the advancement of the department's efforts to achieve pharmaceutical care are integral for the future success of the department. Design of programs for all major positions/classifications should be considered. These programs must be developed in concert with the employees affected. In the future, these programs can demonstrate enhanced outcomes for patient care by ensuring appropriately trained and credentialed employees. This will require a commitment to advanced human resources planning.