Alterations in cardiac dihydropyridine receptors and calcium channel function in mdx mice

Duchenne muscular dystrophy (DMD) is a fatal neuromuscular condition affecting approximately one in 3500 live male births resulting from the lack of the myocyte protein dystrophin. The absence of dystrophin in cardiac myocytes is associated with calcium overload which in turn activates calcium-dependent proteolytic enzymes contributing to congestive heart failure, muscle necrosis and fibrosis. To date, the basis for the calcium overload has not been determined. Since L-type calcium channels are a major mediator of calcium influx we determined their potential contribution to the calcium overload. Male muscular dystrophy (mdx) mice and control C57BL10ScSn (C57) mice aged 12– 16 weeks were used in all experiments. In tissue bath studies, isolated contracting left atria from mdx revealed a reduced potency to the dihydropyridine (DHP) agonist BayK8644 and antagonist nifedipine (P < 0.05). Similarly, radioligand binding studies using the DHP antagonist [3H]-PN 200-110 showed a reduced potency (P < 0.05) in isolated membranes, associated with an increased receptor density (P < 0.05). The increased receptor density was supported by RT-PCR experiments revealing increased RNAfor the DHP receptor. Patch clamp studies revealed the presence of a diltiazem sensitive calcium current that showed delayed inactivation in isolated mdx myocytes (P < 0.01). In conclusion, the increased number of DHP binding sites and the delay in L-type current inactivation may both contribute to increased calcium influx and hence calcium overload in the dystrophin deficient mdx cardiac myocytes.

How well does B-type natriuretic peptide predict death and cardiac events in patients with heart failure: systematic review

Objective To assess how well B-type natriuretic peptide (BNP) predicts prognosis in patients with heart failure. Design Systematic review of studies assessing BNP for prognosis m patients with heart failure or asymptomatic patients. Data sources Electronic searches of Medline and Embase from January 1994 to March 2004 and reference lists of included studies. Study selection and data extraction We included all studies that estimated the relation between BNP measurement and the risk of death, cardiac death, sudden death, or cardiovascular event in patients with heart failure or asymptomatic patients, including initial values and changes in values in response to treatment. Multivariable models that included both BNP and left ventricular ejection fraction as predictors were used to compare the prognostic value of each variable. Two reviewers independently selected studies and extracted data. Data synthesis 19 studies used BNP to estimate the relative risk of death or cardiovascular events in heart failure patients and five studies in asymptomatic patients. In heart failure patients, each 100 pg/ml increase was associated with a 35% increase in the relative risk of death. BNP was used in 35 multivariable models of prognosis. In nine of the models, it was the only variable to reach significance-that is, other variables contained no prognostic information beyond that of BNP. Even allowing for the scale of the variables, it seems to be a strong indicator of risk. Conclusion Although systematic reviews of prognostic studies have inherent difficulties, including die possibility of publication bias, the results of the studies in this review show that BNP is a strong prognostic indicator for both asymptomatic patients mid for patients with heart failure at all stages of disease.

Cited2 is required both for heart morphogenesis and establishment of the left-right axis in mouse development

Establishment of the left-right axis is a fundamental process of vertebrate embryogenesis. Failure to develop left-right asymmetry leads to incorrect positioning and morphogenesis of numerous internal organs, and is proposed to underlie the etiology of several common cardiac malformations. The transcriptional modulator Cited2 is essential for embryonic development: Cited2-null embryos die during gestation with profound developmental abnormalities, including cardiac malformations, exencephaly and adrenal agenesis. Cited2 is also required for normal establishment of the left-right axis; we demonstrate that abnormal heart looping and right atrial and pulmonary isomerism are consistent features of the left-right-patterning defect. We show by gene expression analysis that Cited2 acts upstream of Nodal, Lefty2 and Pitx2 in the lateral mesoderm, and of Lefty1 in the presumptive floor plate. Although abnormal left-right patterning has a major impact on the cardiac phenotype in Cited2-null embryos, laterality defects are only observed in a proportion of these embryos. We have therefore used a combination of high-resolution imaging and three-dimensional (3D) modeling to systematically document the full spectrum of Cited2-associated cardiac defects. Previous studies have focused on the role of Cited2 in cardiac neural crest cell development, as Cited2 can bind the transcription factor Tfap2, and thus affect the expression of Erbb3 in neural crest cells. However, we have identified Cited2-associated cardiac defects that cannot be explained by laterality or neural crest abnormalities. In particular, muscular ventricular septal defects and reduced cell density in the atrioventricular (AV) endocardial cushions are evident in Cited2-null embryos. As we found that Cited2 expression tightly correlated with these sites, we believe that Cited2 plays a direct role in development of the AV canal and cardiac septa. We therefore propose that, in addition to the previously described reduction of cardiac neural crest cells, two other distinct mechanisms contribute to the spectrum of complex cardiac defects in Cited2-null mice; disruption of normal left-right patterning and direct loss of Cited2 expression in cardiac tissues.

Dizziness after traumatic brain injury: Overview and measurement in the clinical setting

Traumatic brain injury (TBI) may result in a variety of cognitive, behavioural and physical impairments. Dizziness has been reported in up to 80% of cases within the first few days after injury. The literature was reviewed to attempt to delineate prevalence of dizziness as a symptom, impairments causing dizziness, the functional limitations it causes and its measurement. The literature provides widely differing estimates of prevalence and vestibular system dysfunction appears to be the best reported of impairments contributing to this symptom. The variety of results is discussed and other possible causes for dizziness were reviewed. Functional difficulties caused by dizziness were not reported for this population in the literature and review of cognitive impairments suggests that existing measurement tools for dizziness may be problematic in this population. Research on the functional impact of dizziness in the TBI population and measurement of these symptoms appears to be warranted.

Quality of diabetes care and coronary heart disease absolute risk in patients with type 2 diabetes mellitus in Australian general practice

Objective: To examine the quality of diabetes care and prevention of cardiovascular disease (CVD) in Australian general practice patients with type 2 diabetes and to investigate its relationship with coronary heart disease absolute risk (CHDAR). Methods: A total of 3286 patient records were extracted from registers of patients with type 2 diabetes held by 16 divisions of general practice (250 practices) across Australia for the year 2002. CHDAR was estimated using the United Kingdom Prospective Diabetes Study algorithm with higher CHDAR set at a 10 year risk of >15%. Multivariate multilevel logistic regression investigated the association between CHDAR and diabetes care. Results: 47.9% of diabetic patient records had glycosylated haemoglobin (HbA1c) >7%, 87.6% had total cholesterol >= 4.0 mmol/l, and 73.8% had blood pressure (BP) >= 130/85 mm Hg. 57.6% of patients were at a higher CHDAR, 76.8% of whom were not on lipid modifying medication and 66.2% were not on antihypertensive medication. After adjusting for clustering at the general practice level and age, lipid modifying medication was negatively related to CHDAR (odds ratio (OR) 0.84) and total cholesterol. Antihypertensive medication was positively related to systolic BP but negatively related to CHDAR (OR 0.88). Referral to ophthalmologists/optometrists and attendance at other health professionals were not related to CHDAR. Conclusions: At the time of the study the diabetes and CVD preventive care in Australian general practice was suboptimal, even after a number of national initiatives. The Australian Pharmaceutical Benefits Scheme (PBS) guidelines need to be modified to improve CVD preventive care in patients with type 2 diabetes.

Overweight and obesity increase the risk of coronary heart disease: A pooled analysis of 30 prospective studies

The importance of overweight as a risk factor for coronary heart disease (CHD) remains unsettled. We estimated the relative risk (RR) for CHD associated with underweight (body mass index, BMI < 20 kg/m2), overweight (25 – 30 kg/m2) and obesity (= 30 kg/m2), compared with normal weight (20 – 25 kg/m2) in a random effects meta-analysis of 30 prospective studies, including 389,239 healthy, predominantly Caucasian persons. We also explored sources of heterogeneity between studies and examined effects of systematic adjustment for confounding and intermediary variables. Pooled age-, sex- and smoking-adjusted RRs (95% confidence interval) for overweight, obesity and underweight compared with normal weight were 1.33 (1.24 – 1.43), 1.69 (1.44 – 1.99) and 1.01 (0.85 – 1.20), respectively. Stratified analyses showed that pooled RRs for BMI were higher for studies with longer follow-up (= vs. < 15 years) and younger populations (< vs. = 60 years). Additional adjustment for blood pressure, cholesterol levels and physical activity decreased the RR per 5 BMI units from 1.28 (1.21 – 1.34) to 1.16 (1.11 – 1.21). We conclude that overweight and obesity are associated with a substantially increased CHD risk in Caucasians, whereas underweight is not. Prevention and reduction of overweight and obesity, therefore, remain of importance for preventing CHD.

Multifidus muscle recovery is not automatic after resolution of acute, first-episode low back pain

Study Design. A clinical study was conducted on 39 patients with acute, first-episode, unilateral low back pain and unilateral, segmental inhibition of the multifidus muscle. Patients were allocated randomly to a control or treatment group. Objectives. To document the natural course of lumbar multifidus recovery and to evaluate the effectiveness of specific, localized, exercise therapy on muscle recovery. Summary of Background Data. Acute low back pain usually resolves spontaneously, but the recurrence rate is high. Inhibition of multifidus occurs with acute, first-episode, low back pain, and pathologic changes in this muscle have been linked with poor outcome and recurrence of symptoms. Methods. Patients in group 1 received medical treatment only. Patients in group 2 received medical treatment and specific, localized, exercise therapy. Outcome measures for both groups included 4 weekly assessments of pain, disability, range of motion, and size of the multifidus cross-sectional area. Independent examiners were blinded to group allocation. Patients were reassessed at a 10-week follow-up examination. Results. Multifidus muscle recovery was not spontaneous on remission of painful symptoms in patients in group 1. Muscle recovery was more rapid and more complete in patients in group 2 who received exercise therapy (P = 0.0001). Other outcome measurements were similar for the two groups at the 4-week examination. Although they resumed normal levels of activity, patients in group 1 still had decreased multifidus muscle size at the 10-week follow-up examination. Conclusions. Multifidus muscle recovery is not spontaneous on remission of painful symptoms. Lack of localized, muscle support may be one reason for the high recurrence rate of low back pain following the initial episode.

A comparison of computer-based methods for the determination of onset of muscle contraction using electromyography

Little consensus exists in the literature regarding methods for determination of the onset of electromyographic (EMG) activity. The aim of this study was to compare the relative accuracy of a range of computer-based techniques with respect to EMG onset determined visually by an experienced examiner. Twenty-seven methods were compared which varied in terms of EMG processing (low pass filtering at 10, 50 and 500 Hz), threshold value (1, 2 and 3 SD beyond mean of baseline activity) and the number of samples for which the mean must exceed the defined threshold (20, 50 and 100 ms). Three hundred randomly selected trials of a postural task were evaluated using each technique. The visual determination of EMG onset was found to be highly repeatable between days. Linear regression equations were calculated for the values selected by each computer method which indicated that the onset values selected by the majority of the parameter combinations deviated significantly from the visually derived onset values. Several methods accurately selected the time of onset of EMG activity and are recommended for future use. Copyright (C) 1996 Elsevier Science Ireland Ltd.

The intercalated disc of monkey myocardial cells and Purkinje fibers as revealed by scanning electron microscopy

The intercalated discs of working myocardium and Purkinje fibers of the monkey heart were examined by scanning and transmission electron microscopy. The NaOH/ultrasonication technique resulted in the digestion of connective tissue and a separation of the intercellular junctions of intercalated discs, such that these could be visualized three-dimensionally. The intercalated discs of ventricular myocytes, atrial myocytes and Purkinje fibers vary considerably in number and configuration, as do the intercalated discs of the three different layers of the ventricular myocardium. Myocytes in the subepicardial, middle and subendocardial layers of the ventricle have 1-3, 4-5 and 5-6 intercalated discs at the end of these cells, respectively, Those in the endocardial layer are characterized by the presence of small laterally-placed intercalated discs. Atrial myocytes and Purkinje fibers usually only have 1-2 intercalated discs, Individual intercalated discs in ventricular myocytes have complicated stairs with 10-30 steps and corresponding risers, while those of atrial myocytes and Purkinje fibers have simple stairs with 1-3 steps and risers, Steps equivalent to the plicate segments are characterized by densely-packed microplicae and finger-like microprojections which greatly increase surface area in vertricular myocytes, Microprojections in atrial myocytes and Purkinje fibers are sparse by comparison, Risers equivalent to the interplicate segments containing large gap junctional areas are most numerous in left ventricular myocytes, followed by right ventricular myocytes, Purkinje fibers and atrial myocytes in decreasing order. The geometric arrangement of the various types of myocytes may be related with impulse propagation. Large intercalated discs of cell trunks and series branches may participate in longitudinal propagation, while small laterally-placed ones may be the site of transverse propagation.

Effects of (-)-RO363 at human atrial beta-adrenoceptor subtypes, the human cloned beta(3)-adrenoceptor and rodent intestinal beta(3)-adrenoceptors

1 Chronic treatment of patients with beta-blockers causes atrial inotropic hyperresponsiveness through beta(2)-adrenoceptors, 5-HT4 receptors and H-2-receptors but apparently not through beta(1)-adrenoceptors despite data claiming an increased beta(1)-adrenoceptor density from homogenate binding studies. We have addressed the question of beta(1)-adrenoceptor sensitivity by determining the inotropic potency and intrinsic activity of the beta(1)-adrenoceptor selective partial agonist (-)-RO363 and by carrying out both homogenate binding and quantitative beta-adrenoceptor autoradiography in atria obtained from patients treated or not treated with beta-blockers. In the course of the experiments it became apparent that (-)-RO363 also may cause agonistic effects through the third atrial beta-adrenoceptor. To assess whether (-)-RO363 also caused agonistic effects through beta(3)-adrenoceptors we studied its relaxant effects in rat colon and guinea-pig ileum, as well as receptor binding and adenylyl cyclase stimulation of chinese hamster ovary (CHO) cells expressing human beta(3)-adrenoceptors. 2 beta-Adrenoceptors were labelled with (-)-[I-125]-cyanopindolol. The density of both beta(1)- and beta(2)-adrenoceptors was unchanged in the 2 groups, as assessed with both quantitative receptor autoradiography and homogenate binding. The affinities of (-)-RO363 for beta(1)-adrenoceptors (pK(i) = 8.0-7.7) and beta(2)-adrenoceptors (pK(i) = 6.1-5.8) were not significantly different in the two groups. 3 (-)-RO363 increased atrial force with a pEC(50) of 8.2 (beta-blocker treated) and 8.0 (non-beta-blocker treated) and intrinsic activity with respect to (-)-isoprenaline of 0.80 (beta-blocker treated) and 0.54 (non-beta-blocker treated) (P<0.001) and with respect to Ca2+ (7 mM) of 0.65 (beta-blocker treated) and 0.45 (non-beta-blocker treated) (P<0.01). The effects of (-)-RO363 were resistant to antagonism by the beta(2)-adrenoceptor antagonist, ICI 118,551 (50 nM). The effects of 0.3-10 nM (-)-RO363 were antagonized by 3-10 nM of the beta(1)-adrenoceptor selective antagonist CGP 20712A. The effects of 20-1000 nM (-)-RO363 were partially resistant to antagonism by 30-300 nM CGP 20712A. 4 (-)-RO363 relaxed the rat colon, partially precontracted by 30 mM KCl, with an intrinsic activity of 0.97 compared to (-)-isoprenaline. The concentration-effect curve to (-)-RO363 revealed 2 components, one antagonized by (-)-propranolol (200 nM) with pEC(50)=8.5 and fraction 0.66, the other resistant to (-)-propranolol (200 nM) with pEC(50)=5.6 and fraction 0.34 of maximal relaxation. 5 (-)-RO363 relaxed the longitudinal muscle of guinea-pig ileum, precontracted by 0.5 mu M histamine, with intrinsic activity of 1.0 compared to (-)-isoprenaline and through 2 components, one antagonized by (-)-propranolol (200 nM) with pEC(50)=8.7 and fraction 0.67, the other resistant to (-)-propranolol with pEC(50)=4.9 and fraction 0.33 of maximal relaxation. 6 (-)-RO363 stimulated the adenylyl cyclase of CHO cells expressing human beta(3)-adrenoceptors with pEC(50)=5.5 and intrinsic activity 0.74 with respect to (-)-isoprenaline (pEC(50)=5.9). (-)-RO363 competed for binding with [I-125]cyanopindolol at human beta(3)-adrenoceptors transfected into CHO cells with pK(i)=4.5. (-)-Isoprenaline (pk(i)=5.2) and (-)-CGP 12177A (pK(i)=6.1) also competed for binding at human beta(2)-adrenoceptors. 7 We conclude that under conditions used in this study, (-)-RO363 is a potent partial agonist for human beta(1)- and beta(3)-adrenoceptors and appears also to activate the third human atrial beta-adrenoceptor. (-)-RO363 relaxes mammalian gut through both beta(1)- and beta(3)-adrenoceptors. (-)-RO363, used as a beta(1)-adrenoceptor selective tool, confirms previous findings with (-)-noradrenaline that beta(1)-adrenoceptor mediated atrial effects are only slightly enhanced by chronic treatment of patients with beta-blockers. Chronic treatment with beta(1)-adrenoceptor-selective blockers does not significantly increase the density of human atrial beta(1)- and beta(2)-adrenoceptors.