The ultrastructure and flexibility of thylakoid membranes in leaves and isolated chloroplasts as revealed by small-angle neutron scattering.

We studied the periodicity of the multilamellar membrane system of granal chloroplasts in different isolated plant thylakoid membranes, using different suspension media, as well as on different detached leaves and isolated protoplasts-using small-angle neutron scattering. Freshly isolated thylakoid membranes suspended in isotonic or hypertonic media, containing sorbitol supplemented with cations, displayed Bragg peaks typically between 0.019 and 0.023Å(-1), corresponding to spatially and statistically averaged repeat distance values of about 275-330 Å⁻¹. Similar data obtained earlier led us in previous work to propose an origin from the periodicity of stroma thylakoid membranes. However, detached leaves, of eleven different species, infiltrated with or soaked in D2O in dim laboratory light or transpired with D2O prior to measurements, exhibited considerably smaller repeat distances, typically between 210 and 230 Å⁻¹, ruling out a stromal membrane origin. Similar values were obtained on isolated tobacco and spinach protoplasts. When NaCl was used as osmoticum, the Bragg peaks of isolated thylakoid membranes almost coincided with those in the same batch of leaves and the repeat distances were very close to the electron microscopically determined values in the grana. Although neutron scattering and electron microscopy yield somewhat different values, which is not fully understood, we can conclude that small-angle neutron scattering is a suitable technique to study the periodic organization of granal thylakoid membranes in intact leaves under physiological conditions and with a time resolution of minutes or shorter. We also show here, for the first time on leaves, that the periodicity of thylakoid membranes in situ responds dynamically to moderately strong illumination. This article is part of a special issue entitled: photosynthesis research for sustainability: keys to produce clean energy.

Visual outcomes following ICG assisted ILM peel for Macular Hole.

PURPOSE: To evaluate the anatomical and visual outcome of indocyanine green (ICG)-assisted internal limiting membrane (ILM) peeling for macular hole surgery. A literature search identified potential factors that may affect the functional success of the procedure. METHODS: Retrospective case note review of 14 consecutive patients undergoing phaco-vitrectomy, gas and ICG-assisted ILM peeling for macular hole from July 2001 to July 2002. A 0.5% ICG solution (osmolarity 270 mOsm) was left in contact with the retina for 1-3 min. The outcome measures were hole closure, change in visual acuity, and macular pigmentary changes. RESULTS: Anatomical hole closure was achieved in 13 of 14 eyes (92.8%). The mean logMAR Snellen acuities were 0.80 (range 0.60-1.30) preoperatively and 0.77 (0.48-1.30) postoperatively. Seven eyes (50%) developed retinal pigmentary changes in the macular area. CONCLUSIONS: ICG-assisted ILM peeling for macular hole surgery achieves high rates of anatomical hole closure, but functional results are less encouraging. Previous studies suggest toxicity of the ICG to the retina, at the level of the RPE or inner retina. The results may be optimized by using a lower concentration, iso-osmolar, viscous solution, and by minimizing contact time of the solution and intensity, and duration of illumination.

Modification of anomalous swelling in multilamellar vesicles induced by alkali halide salts.

By use of small-angle X-ray scattering it is shown that addition of alkali halide salts in small amounts (0-200 mM) shifts the repeat spacing in multilamellar DC13PC vesicles and alters the anomalous swelling behaviour close to the main transition. Both effects follow the Hofmeister series of the ions. We suggest that the shift of repeat spacing can be explained by ion effects on the van der Waals attractive forces between the membranes and on the decay length of the repulsive hydration force. The anomalous swelling is explained in terms of a critical unbinding of the membranes. The proximity of the critical temperature of the unbinding to the main transition temperature can be tuned by varying the concentration and type of salt in the sample.

Effects of the beta 2-adrenoceptor agonists fenoterol and salbutamol on force of contraction in isolated human ventricular myocardium.

The effects of fenoterol and salbutamol on isometric force of contraction were studied in isolated, electrically driven human papillary muscle preparations. Fenoterol increased force of contraction at concentrations of 1 mumol l-1 and higher. The maximally effective concentration of fenoterol (100 mumol l-1) increased force of contraction by about 130%. The positive inotropic effect of fenoterol was not influenced by 0.1 mumol l-1 prazosin. The beta 1-selective antagonist atenolol (2 mumol l-1) and the beta 2-selective antagonist ICI 118551 (1 mumol l-1) shifted the concentration-response curve of fenoterol to the right, indicating that beta 1- and beta 2-adrenoceptors may contribute to the positive inotropic effect of fenoterol. In contrast to fenoterol, salbutamol increased force of contraction only by about 11% at 100 mumol l-1. The results indicate that: (1) fenoterol exerts a direct positive inotropic effect in the human heart which may support the beneficial effects of the reduction of systemic vascular resistance in patients with congestive heart failure; (2) this positive inotropic effect of fenoterol is mediated by beta 1- and beta 2-adrenoceptors; (3) the clinically observed improvement of cardiac performance in the case of salbutamol is presumably not due to any direct positive inotropic effect.