Systems information and effective action

Two types of problem may be associated with systems information: insufficient information or too much of it. Either way, effective action is unlikely. Action and effect are concepts belonging to the idea of sequentiality: first action, then the effect. If there is a perceptible effect, there must have been an action. Effective action is aimed at a specific purpose or goal: in other words, it is planned action. Problems in the exchange of information are examined, and it is suggested how action should be made more effective.     

Intracellular pH in vascular smooth muscle: regulation by sodium-hydrogen exchange and multiple sodium dependent HCO3- mechanisms

OBJECTIVES: The aim was to determine the mechanisms, particularly bicarbonate dependent mechanisms, of intracellular pH (pHi) recovery from various acidoses in vascular smooth muscle and to explore the ATP dependency of the respective mechanisms. METHODS: Experiments were conducted in rat aortic smooth muscle cells grown in primary culture and synchronised in a non-growing state by serum deprivation. pHi was measured in cells loaded with the pH sensitive fluorescent dye, 2',7'-bis-(2-carboxyethyl)-5-(and 6)-carboxyfluorescein (BCECF). Chloride efflux was studied by determination of the rate of efflux of 36Cl over 5 min. Cells were ATP depleted by substitution of glucose in the medium by 2-deoxyglucose. Acidoses were induced by CO2 influx and NH3 efflux techniques. RESULTS: In the absence of HCO3-, the 5-(N-ethyl-N-isopropyl) amiloride (EIPA) sensitive Na+/H+ exchange accounted for the recovery from intracellular acidosis. In the presence of HCO3- ions the response to respiratory acidosis (CO2 influx) was predominantly via activation of Na+/H+ exchange and an EIPA sensitive Na+ and HCO3- dependent mechanism. A 4-acetamido-4'-isothiocyanostilbene-2',2'-sulphonic acids (SITS) sensitive Na+ dependent Cl-/HCO3- mechanism which is also sensitive to EIPA makes a small contribution during severe intracellular acidosis. Under such conditions HCO3- dependent mechanisms contributed about 40% to the overall pHi regulating capacity of vascular smooth muscle cells. However, under conditions which deplete cellular ATP these pHi regulating mechanisms account for virtually all of theses cells' ability to regulate pHi. The inability of Na+/H+ exchange to participate in pHi recovery under these circumstances, reduces the ability of vascular smooth muscle cells to recover pHi by approximately 50-60%. Chloride efflux was approximately linear over 5 min and was increased by 36% in the presence of extracellular HCO3-. Efflux in the presence of HCO3- was inhibited similarly by both SITS and EIPA. CONCLUSIONS: At least three transporters contribute to recovery from acidosis in vascular smooth muscle: Na+/H+ exchange, an Na(+)-HCO3- cotransporter which is sensitive to EIPA, and an Na+ dependent HCO3-/Cl- exchange sensitive to both SITS and EIPA. The Na(+)-HCO3- cotransporter appears to be similar to that described in human vascular smooth muscle. When the Na+/H+ exchanger is attenuated by cellular ATP depletion, the alternative pathways, particularly the Na(+)-HCO3- cotransporter, ensure that substantial pHi regulatory capacity is maintained.     

Stereotactic ventrolateral thalamotomy: is ventriculography necessary?

In the computed tomography/magnetic resonance imaging (CT/MRI) era, the need for ventriculography to perform ventrolateral thalamotomy accurately has been debated. We retrospectively compared CT/MRI-derived coordinates for ventrolateral thalamotomy with the final lesion coordinates that were determined by ventriculography and microelectrode recording in 74 thalamotomies performed from 1984 to 1994. The median three-dimensional distance between the CT/MRI-derived loci and the ventriculography/microelectrode loci was 4.7 mm (range, 1.0-11.7 mm). The techniques correlated least along the Y axis (median, -0.3 mm; range, -8.2 to 8.0 mm). Correlation along the X axis was most consistent (median, 0.5 mm; range, -4.2 to 5.0 mm). Since 1990, the CT/MRI-derived coordinates have been generated by a multimodality correlative imaging technique (MCIT). A comparison of thalamotomies performed with and without the MCIT revealed a significant improvement in the correlation of CT/MRI- and ventriculography/microelectrode-derived coordinates when the MCIT was employed. The greatest improvement was noted along the Y axis where the median absolute difference was reduced from 4.0 to 1.8 mm (P = 0.0001). The result was a statistically significant reduction in the median three-dimensional distance from 5.6 to 3.7 mm (P = 0.0007). The authors conclude that thalamotomies can be safely and effectively performed without ventriculography when the MCIT is employed and supported by neurophysiological monitoring.     

In situ EXAFS studies of modifications to supported metallic catalysts under reactive atmospheres

Extended X-ray absorption fine structure (EXAFS) spectroscopy has been used to study the structural evolution of monometallic (Pt/Al₂O₃) and bimetallic (Pt-Re/Al₂O₃) catalysts with metal loadings representative of those used industrially under conditions close to those seen during preparation (calcination and reduction), during catalysis (under a hydrogen-hydrocarbon mixture), and during regeneration (simulated by cycles of reduction and oxidation). During the catalytic reforming ofn-heptane, the formation of bonds to carbon species is observed directly by EXAFS. Despite the fact that only platinum-carbon bonds are observed, bimetallic systems show significant differences compared with monometallic systems with, in the case of Pt-Re, a reduction in the temperature range over which carbon bonding is observed, and structural modifications of the metallic particles. Under the same conditions, no carbon bonding is observed for the Pt-Sn system. In the case of Pt-Sn/Al₂O₃, the EXAFS results, confirmed by transmission electron microscopy, demonstrate the high resistance to sintering of this bimetallic system compared to the monometallic system.     

Primary craniosynostosis: imaging features

In 1851, Virchow introduced the term craniosynostosis to describe a variety of abnormalities in calvarial growth. These skull deformities are usually apparent in infancy. When an abnormal calvarial configuration is detected, a radiologic evaluation is necessary to characterize the deformity and to guide the corrective surgical procedure. Affected children are believed to have an improved outcome when diagnosis and surgical intervention occur at an early age. CT with three-dimensional reconstruction optimally evaluates the presence and degree of sutural involvement and assesses associated facial and intracranial abnormalities. This pictorial essay illustrates the imaging findings, nomenclature, and associated abnormalities of the various types of primary craniosynostosis.