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Biomedical subjects

H Reuter

Publications and source records attributed to H Reuter.

226 records · Page 13Linked to original sources
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Calcium channel modulation by neurotransmitters, enzymes and drugs.

Calcium channels in excitable membranes are of great importance for many cellular functions. Modulation of these channels by neurotransmitters and drugs regulates calcium influx into the cell and thereby alters the functional state of the cell. Recently it has become possible to measure properties of single calcium channels directly and to obtain evidence on mechanisms of their modulation.

Animals↗
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Ca2+ channel modulation by 8-bromocyclic AMP in cultured heart cells.

Modulation of ion channels is of increasing interest as it is an important step in the regulation of cellular functions. We have analysed the effect of 8-bromocyclic AMP on Ca2+ channels in cultured cardiac cells by the patch-clamp method and report here that there was a large increase in the probability of opening of the channels. On the basis of a recently proposed kinetic reaction scheme we suggest that cyclic AMP-dependent phosphorylation of Ca2+ channels primarily promotes the forward rate constants which lead to the open state of a Ca2+ channel during depolarization.

8-Bromo Cyclic Adenosine Monophosphate↗
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Ion channels in human neutrophils activated by a rise in free cytosolic calcium concentration.

A rapid, transient rise in the free cytosolic Ca2+ concentration ([Ca2+]i) is one of the earliest events in neutrophil activation and is assumed to be involved in many of the subsequent cellular reactions. Both Ca2+ release from intracellular stores and Ca2+ influx from the extracellular space contribute to the rise in [Ca2+]i. In an attempt to assess the relative importance of these pools and the sequences leading to the rise in [Ca2+]i, we have studied the time course of changes in [Ca2+]i after stimulation with N-formyl-methionyl-leucyl-phenylalanine (fMLP) or platelet-activating factor (PAF) using the Ca2+ indicators quin-2 and fura-2. We observed a time lag of 1-3 s between stimulation and rise in [Ca2+]i. This lag depends on the agonist concentration but is independent of extracellular Ca2+. Thus Ca2+ release from intracellular stores is rate limiting for the rise in [Ca2+]i. After this, cation channels in the plasma membrane (measured with the patch clamp method) are opened. These non-selective channels, which also pass Ca2+, are activated by the initial rise in [Ca2+]i, but by neither fMLP nor inositol 1,4,5-trisphosphate (IP3) directly.

Calcium↗
PubMedDate not supplied

Twelve-lead electrocardiography in tuberculous pericarditis.

OBJECTIVES: This study is part of an ongoing initiative started in 1995 to investigate the therapeutic efficacy of adjuvant corticosteroids in the management of tuberculosis (TB) pericarditis. In this retrospective, descriptive study we describe the changes found on the 12-lead electrocardiogram (ECG) in patients with TB pericarditis, with and without cardiac tamponade. We determined the diagnostic accuracy of ECG parameters for cardiac tamponade. METHODS: All patients referred to our department with echocardiographically confirmed large pericardial effusions underwent a thorough clinical assessment followed by pericardiocentesis and drainage using an indwelling pigtail catheter. The amount of drained effusion was measured, and fluid was sent for diagnostic assessment. Patients were grouped into those with or without cardiac tamponade. The following ECG parameters were assessed: rate, rhythm, microvoltage, electrical alternans, PR segment and ST segment abnormalities. RESULTS: Of the 157 patients assessed, 88 were diagnosed with TB pericarditis All had abnormal ECGs and 83% had changes of chronic pericarditis. Microvoltage in the extremity and/or precordial leads correlated with the presence of large effusions (> 750 ml). None of the studied parameters correlated with the presence of cardiac tamponade. CONCLUSIONS: Twelve-lead ECG is of supportive but not diagnostic value in cardiac tamponade. The presence of microvoltage suggests the presence of a large effusion. The absence of microvoltage makes the presence of cardiac tamponade unlikely.

Cardiac Tamponade↗
PubMedDate not supplied

Infective endocarditis: improving the diagnostic yield.

INTRODUCTION: Isolating aetiological agents in patients with infective endocarditis (IE) remains problematical. We postulated that the high local incidence of culture-negative IE resulted from antibiotic exposure prior to blood cultures and that a structured delay in therapy in the subacute presentation would improve the diagnostic yield. AIM: We aimed to prospectively observe the diagnostic approach and give an overview of supplementary laboratory tests. STUDY DESIGN: Patients with suspected IE were enrolled into this analytical observational study and followed up for six months (n = 92). We compared the diagnostic yield and outcome in cases where antibiotics were withheld for 72 hours, with those cases who received early antimicrobials, despite being deemed safe for delayed therapy. RESULTS: Definitive diagnoses (definite or excluded IE) were made in 92.8% of patients where antibiotics were delayed, compared to 60% of patients who received empirical treatment (p = 0.08). The mortality rates were 18.4% and 30.0% (p = 0.18). Twenty-three of 26 patients with definite culture-negative IE received antibiotics during the 48 hours preceding cultures, compared to eight of 21 culture-positive patients (P < 0.001). Screening for atypical bacteria did not improve the yield. C-reactive protein (CRP) had a sensitivity of 97.0% (negative predictive value 87.5%), whereas a positive rheumatoid factor (RF) had a specificity of 93.8% (positive predictive value 91.7%). CONCLUSIONS: We observed tendencies towards a greater diagnostic yield and lower mortality where antibiotics were initially withheld. Antibiotic prior to blood cultures were an important cause of culture-negative IE. A normal CRP proved useful in excluding IE; a positive RF strongly favoured IE.

Anti-Bacterial Agents↗
PubMedDate not supplied

Role of chest radiography in diagnosing patients with tuberculous pericarditis.

AIM: To describe the abnormalities on chest X-ray (CXR) in patients presenting with tuberculous pericardial effusions. METHODS: One hundred and seventy patients presented to Tygerberg Hospital with large pericardial effusions (epi-pericardial separation > 10 mm). All patients had a diagnostic work-up, which included CXR, ECG, two-dimensional echocardiography and HIV serology. Echocardiography was followed by pericardiocentesis and drainage. Pericardial fluid was analysed for adenosine deaminase (ADA), Ziehl Neelsen (ZN) stain, bacterial and mycobacterial cultures. Sputum was sent for ZN stain and mycobacterial cultures. Tuberculous pericardial effusions were diagnosed according to predetermined criteria. RESULTS: The diagnosis of tuberculous pericarditis was made in 53% (n = 90) of patients with pericardial effusions. Forty-one of the subjects (45.5%) were HIV positive. All patients had an enlarged cardiac silhouette and in the majority of cases, the cardiac shadow was globular with distinct margins. The cardiothoracic ratio (CTR) exceeded 0.55 in all patients. The amount of fluid drained correlated with the radiographic finding of cardiac enlargement. CONCLUSION: In developing countries where TB is very prevalent, CXR plays an important role in the identification of large pericardial effusions. Although sonography will still be required for a definite diagnosis, the results of this study show that CXR is a useful screening tool.

Echocardiography↗