Pulpal effects of argon: fluoride excimer laser irradiation and acid-etching of rat molar enamel.

The reaction of enamel, dentine and pulpal tissues to exposure from a laser beam has been shown to depend on the type of laser medium used. The objective of this study was to examine the pulpal response in rat molars after external enamel surface treatment with either an Ar:F excimer laser or acid-gel application. Maxillary right molar occlusal surfaces in 22 animals were irradiated (energy density = 45.0 J/cm2). Maxillary left molar occlusal surfaces were treated with 37 per cent phosphoric acid for 30 s. Untreated mandibular right molars served as controls. At two postoperative time periods (1 and 6 weeks), molars were removed, sectioned, stained (H&E) and scored. Data analysis indicated no significant difference between Ar:F irradiation and controls at 1 week. Treatment with laser or acid-etching left a similar degree of pathosis at 1 and 6 weeks. Although the Ar:F excimer laser produced a more exaggerated pulp response than controls at 6 weeks, tissue vitality was maintained. The Ar:F excimer laser may be useful for ablating vital tooth structure since pulpal tissue in rat molars exhibited no damage in response to low-power irradiation.

Experimental resolution of cooperative free energies for the ten ligation species of cobalt(II)/iron(II)-CO hemoglobin.

Cooperative free energies have been determined for the 10 ligation species of human hemoglobin in the Co(II)/Fe(II)-CO system. In this system, subunits containing unligated cobaltous hemes coexist in the same tetramer with naturally occurring ferrous hemes that are ligated with carbon monoxide. Tetramers comprising the 10 structurally unique combinations of ligated and unligated subunits were characterized in terms of their dimer-tetramer assembly free energies. By use of the thermodynamic linkage between assembly and ligation, the experimentally resolved values were used to obtain the corresponding cooperative free energies (i.e., the differences between actual free energies of ligation and the summed contributions of intrinsic values). The results obtained are in general accord with previous findings on this same system (Imai et al., 1980). The present study extends this earlier work by resolving the cooperative properties of each configurational isomer of the doubly ligated tetramers. The 10 ligation species were found to distribute into 5 discrete cooperative free energy levels according to a combinatorial code which includes, as a special case, the code found previously with cyanomethemoglobin and manganese-substituted hemoglobin (Smith et al., 1987; Daugherty et al., 1991). This distribution exhibits additional characteristics found in the oxygenation of normal ferrous hemoglobin including the quaternary enhancement effect (Mills & Ackers, 1979a,b). These results, and those of the following paper (Doyle et al., 1991), strongly support the premise that a common set of qualitative rules governs the cooperative interactions in hemoglobin irrespective of

Linkage between cooperative oxygenation and subunit assembly of cobaltous human hemoglobin.

The thermodynamic linkage between cooperative oxygenation and dimer-tetramer subunit assembly has been determined for cobaltous human hemoglobin in which iron(II) protoporphyrin IX is replaced by cobalt(II) protoporphyrin IX. The equilibrium parameters of the linkage system were determined by global nonlinear least-squares regression of oxygenation isotherms measured over a range of hemoglobin concentrations together with the deoxygenated dimer-tetramer assembly free energy determined independently from forward and reverse reaction rates. The total cooperative free energy of tetrameric cobalt hemoglobin (over all four binding steps) is found to be 1.84 (+/- 0.13) kcal, compared with the native ferrous hemoglobin value of 6.30 (+/- 0.14) kcal. Detailed investigation of stepwise cooperativity effects shows the following: (1) The largest change occurs at the first ligation step and is determined on model-independent grounds by knowledge of the intermediate subunit assembly free energies. (2) Cooperativity in the shape of the tetrameric isotherm occurs mainly during the middle two steps and is concomitant with the release of quaternary constraints. (3) Although evaluation of the pure tetrameric isotherm portrays identical binding affinity between the last two steps, this apparent noncooperativity is the result of a "hidden" oxygen affinity enhancement at the last step of 0.48 (+/- 0.12) kcal. This quaternary enhancement energy is revealed by the difference in subunit assembly free energies of the triply and fully ligated species and is manifested visually by the oxygenation isotherms at high versus low hemoglobin concentration. (4) Cobaltous hemoglobin dimers exhibit apparent anticooperativity of 0.49 (+/- 0.16) kcal (presumed to arise from heterogeneity of subunit affinities).(ABSTRACT TRUNCATED AT 250 WORDS)

Direct and indirect pathways of functional coupling in human hemoglobin are revealed by quantitative low-temperature isoelectric focusing of mutant hybrids.

Functional energetic coupling within human hemoglobin has been explored by using quantitative analysis of asymmetric mutant hybrid equilibria. Previous work showed that the free energy of cooperativity is largely attributable to alterations in free energy that accompany changing interactions at the interface between alpha 1 beta 1 and alpha 2 beta 2 dimers [Pettigrew et al. (1982) Proc. Natl. Acad. Sci. U.S.A. 79, 1849]. However, the issue of how cooperativity-linked sites in the molecule are energetically coupled in manifesting cooperative ligation is still not well delineated. In this paper we address the questions of what types of functional coupling pathways are operational in hemoglobin, what some of their characteristics are, and how they are related to one another. By constructing asymmetric mutant hybrid hemoglobins, we can assay how two structurally identical, symmetrically equivalent sites are energetically coupled in manifesting subunit assembly and/or cooperative ligation. Asymmetric hybrid hemoglobins, i.e., those containing a single modified site, cannot be isolated and must be studied in equilibrium with their symmetric parent molecules. In order to study these asymmetric hybrid equilibria, we have developed new theory and quantitation techniques to augment the low-temperature quenching and isoelectric focusing procedures of Perrella et al. [(1978) Anal. Biochem. 88, 212]. Studies of these mutant hybrid hemoglobins have provided evidence for three distinct types of energetic coupling within the hemoglobin tetramer. All alpha 1 beta 2 interface sites examined are involved in cooperativity-linked indirect coupling. Within the context of this indirect "pathway" there exist two different types of direct long-range coupling. One of these classes of direct long-range pathways is linked to cooperative ligand binding while the other class is not.

Oscillatory potentials. History, techniques and potential use in the evaluation of disturbances of retinal circulation.

The oscillatory potentials seem to reflect severe disturbances in the retinal (and perhaps choroidal) circulation. In some cases of diabetic retinopathy with severe microangiopathy, the oscillatory potentials may be selectively reduced or extinguished while the amplitude of the a- and b-waves of the ERG remains normal. A correlation appears to exist between severely reduced oscillatory potentials and a circulatory deficiency in the retina. This selective reduction of the oscillatory potentials during advancing retinopathy is considered to be indirect evidence that they are generated independently from the mechanism producing the primary components (the a- and b-waves). The usefulness of the oscillatory potentials in the prognosis of retinal disease, particularly in diabetic retinopathy, is reviewed. The historical background, the techniques and instrumentation necessary to produce and record them, the experimental data available on the site of their origin, the clinical significance to date and the experimental efforts in our laboratory are summarized.

A patterned macular dystrophy with yellow plaques and atrophic changes.

Three middle-aged male patients are described with a peculiar patterned dystrophy of the macula. The basic lesions are discrete yellow plaques typically confined to the macular area and radiating from the fovea. They appear to be located at the level of the retinal pigment epithelium (RPE). With the passage of time some of the yellow plaques altered in extent and configuration, and atrophic changes appeared or extended. Visual acuity and electrophysiological tests are either normal or only moderately affected. The lesions appear to be distinct from the patterned dystrophies of the retina already described and from other conditions characterised by yellow or white deposits at the level of the RPE.

Electroretinographic changes and choroidal defects in a case of central retinal artery occlusion.

A 62-year-old white woman with hypertensive diabetes had central retinal artery occlusion of her right eye. Serial electroretinographic (ERG) studies demonstrated reversible changes in the scotopic components but permanent reduction of the photopic b-wave. Serial simultaneous fluorescein and indocyanine green angiographic studies demonstrated a perfusion defect in the choroid involving part of the macula which subsided after reopening the retinal circulation. Differential hypoxic susceptibility of the ERG photopic and scotopic b-waves was demonstrated, and changes in the patient's retinal tissue oxygenation were postulated on the basis of retinal and choroidal angiographic studies performed during and after central retinal artery occlusion to account for the observed changes in serial ERGS.