FM sonography in diffuse liver disease: prospective assessment and blinded analysis

FM sonography - a signal-processing technique that uses frequency and phase information as well as amplitude data - shows promise in evaluation of patients with diffuse liver disease. In a prospective blinded review of 37 patients with biopsy-proved liver disease and 42 healthy volunteers, FM sonography was clearly superior to traditional amplitude-based (AM) sonography in distinguishing healthy from diseased subjects. Statistically significant differences were seen in accuracy (FM, 98.7%; AM, 84.8%), sensitivity (FM, 97.3%; AM, 70.3%), and negative predictive value (FM, 97.7%; AM, 78.8%). Our data also suggest that current FM sonographic techniques cannot differentiate among histologic findings associated with different hepatic parenchymal abnormalities. It is unclear, therefore, whether FM imaging can reduce the numbers of patients who require biopsy for diagnosis or the frequency of biopsy procedures in patients with known disease.     

Pneumothorax and other lung diseases: effect of altered resolution and edge enhancement on diagnosis with digitized radiographs

Prior studies have shown that pneumothorax is one of the more difficult entities to diagnose with digitized radiography. This study was designed to test whether increasing resolution from 1.25 to 2.5 line pairs per millimeter (lp/mm) and image processing (edge enhancement from unsharp masking) would increase accuracy and confidence in the diagnosis of pneumothorax, as well as normal cases and other forms of lung disease. Conventional radiographs were digitized with use of a laser reader and then reformatted as film hard copy. Eleven observers read 35 cases reformatted in three different ways (1.25 lp/mm, 2.5 lp/mm, 1.25 lp/mm unsharp mask). The images with finer resolution (2.5 lp/mm) and unsharp mask images were superior to those with coarser resolution (1.25 lp/mm) for the diagnosis of pneumothorax. There was no difference in diagnostic accuracy for normal patients. For abnormalities other than pneumothorax, the unsharp mask images were significantly worse. Confidence in the diagnosis of pneumothorax and other abnormalities was highest with the finest resolution (2.5 lp/mm).     

Specific membrane properties of cat motoneurones

1. Electrophysiological properties of cat motoneurones were measured using intracellular electrodes, after which Procion dye was injected iontophoretically into the neurone through the recording pipette.2. Histological procedures were chosen to minimize changes in neuronal morphology. Reconstructed motoneurones had more dendritic branches and larger surface areas than the Golgi-stained motoneurones of earlier reports.3. The sum of the 3/2 power of the dendritic diameters (the dendritic trunk parameter; Rall, 1959) of the reconstructed motoneurones was found to decrease with distance from the soma. Thus, the dendritic tree is not satisfactorily approximated by a non-tapering membrane cylinder.4. A computational technique was developed to allow calculation of the specific resistance (R(m)) of the membrane using the measured value of the input resistance of the motoneurone and a more detailed approximation of the dendritic tree. These calculations indicate that the average resting value of dendritic R(m) is at least 1800 Omega cm(2). The specific membrane capacity, calculated assuming uniform R(m), ranged between 2-3 muF/cm(2).     

Influence of anomalous rectifier activation on afterhyperpolarizations of neurons from cat sensorimotor cortex in vitro

1. Large neurons from layer V of cat sensorimotor cortex (Betz cells) were studied to determine the influence of the anomalous rectifier current (IAR) on slow afterhyperpolarizations (AHPs). The neurons were examined using intracellular recording and single-microelectrode voltage clamp in an in vitro brain slice preparation. 2. A faster medium-duration AHP (mAHP) and slower AHP (sAHP) followed repetitive firing (22, 23). The amplitude of the mAHP often increased or remained constant during membrane potential hyperpolarization. The membrane potential trajectory resulting solely from IAR activation was similar to the mAHP. 3. Postrepetitive firing voltage clamp was used to measure directly slowly decaying K+ currents (IK) and IAR at different membrane potentials. IK exhibited both a fast and slow decay. The time constants of the fast decay of IK and IAR activation were similar. IAR increased with hyperpolarization or raised extracellular K+ concentration [( K+]o), whereas both the fast and slow components of IK reversed or nulled near -100 mV and behaved as pure K+ currents in response to raised [K+]o. 4. To determine the precise contribution of IK and IAR to the AHP waveform, theoretical AHPs were computed using a quantitative model based on voltage-clamp measurements. The calculated AHPs were qualitatively similar to measured AHPs. The amplitude of the mAHP showed little change with hyperpolarization because of the increasing dominance of IAR at more negative membrane potentials. The sAHP was little affected by IAR activation. 5. Several model parameters subject to biological variation among Betz cells were varied in the calculations to determine their importance in the AHP waveform. With IK parameters held constant, the amplitude and time course of the mAHP depended on resting potential, membrane time constant, the kinetics of the anomalous rectifier conductance (GAR), and the maximum value of GAR. IAR activation could result in a biphasic AHP even when the fast decay of IK was omitted from the calculations. 6. A wider variation of model parameters revealed behavior that may be relevant to other neurons. Certain values of membrane or IAR activation time constants resulted in a monophasic AHP even when the fast decay of IK was present. The decay of a biphasic AHP could reflect either the onset of IAR or the fast decay of IK, depending on the relative value of their time constants. Procedures are outlined to discriminate between these possibilities using current clamp methods.(ABSTRACT TRUNCATED AT 400 WORDS)     

Properties of a persistent inward current in normal and TEA-injected motoneurons

1. Membrane currents of normal and TEA-injected cat lumbar motoneurons were investigated using the technique of somatic voltage clamp. 2. The current-voltage (I-V) relation of healthy motoneurons contains a region of negative slope conductance caused by a persistent inward current component (Ii). In the most striking examples, Ii is net inward at some potentials between 10 and 30 mV positive to resting potential. 3. Near its activation threshold (greater than or equal to 10 mV positive to rest), Ii does not decrement during prolonged voltage steps and, in most cells, activates very slowly. Ii amplitude increases and time to peak Ii decreases with further small increments of depolarization, and Ii decrements during sustained voltage steps. Maximum Ii amplitude occurs 20--30 mV positive to rest in most cells. Ii is not visible at sufficiently large depolarizations. 4. Ii appears to be mixed with potassium current components at nearly every potential where it is visible. These include a slow outward current first activated near Ii activation threshold, a fast outward current additonally activated at larger depolarizing potentials, and a fast, transient outward current that obscures the true onset of Ii at nearly every potential. 5. Ii is not carried by sodium entering via the fast, transient channels and is present after pharmacological blockage of sodium currents. It is proposed that Ii is predominantly carried by calcium ions. 6. The presence of inward tail currents after repolarization from potentials that activate a steady outward current suggest that Ii remains present but hidden at large depolarizations. Ii inactivation was further investigated in TEA-injected motoneurons since Ii and the tail currents are more prominent in these cells. 7. Conventional recordings from TEA-injected motoneurons suggest that a prolonged, postspike plateau potential is maintained by a persistent inward current. Voltage-clamp data can account for the principal features of the plateau potential. 8. Voltage-clamp results in TEA-injected motoneurons suggest that Ii is subject to little or no inactivation at potentials less than or equal to 30 mV positive to rest and to partial inactivation, at most, at higher potentials during steps lasting less than or equal to 100 ms. The apparent decay of Ii during sustained depolarization is caused by the development of a larger outward current. 9. Ii is similar in several ways to a persistent calcium current observed in some molluscan neurons. Theoretical and experimental results suggest that Ii is generated predominantly in a local region under voltage control and that the observed membrane currents govern somatic membrane potential and cell behavior.     

CD40 expression by gingival fibroblasts: correlation of phenotype with function

CD40, a member of the tumor necrosis factor-alpha receptor family, is constitutively expressed by cells of hematopoietic and non- hematopoietic origin, including fibroblasts. Signaling through this receptor molecule regulates inflammatory cytokine secretion by many cell types. Based on the recently described cytokine secretory heterogeneity of fibroblast cell subsets, we hypothesized that secretion of inflammatory cytokines by gingival fibroblast cultures may be dictated by the existence of differential proportions of cytokine- secreting subpopulations which express high levels of CD40. After examining a large number of gingival fibroblast (GF) cultures we find that the frequency of IL-6- and IL-8-secreting cells mirrors the frequency of cells expressing high levels of CD40 in these cultures. In addition, we demonstrate a direct functional relationship between CD40 expression and IL-6 or IL-8 secretion by showing that ligation of this molecule on GF, and CD40+ fibroblast subsets in particular, up- regulates secretion of these cytokines in vitro.