Repeatability of Bruch’s Membrane Opening-minimum Rim Width in Age-related Macular Degeneration and Diabetic Macular Edema

Purpose: To evaluate the repeatability of retinal nerve fiber layer (RNFL) thickness and Bruch’s membrane opening-minimum rim width (BMO-MRW) measurements by spectral-domain optical coherence tomography (SD-OCT) in wet age-related macular degeneration (wAMD) and diabetic macular edema (DME).Methods: This was a prospective study. The RNFL thickness and BMO-MRW parameters for each sector and global average were measured twice by SD-OCT. Repeatability was evaluated using the intraclass correlation coefficient (ICC) and coefficient of variation (CV). If the optic disc membrane was confirmed, it was analyzed by dividing it into three groups based on severity.Results: A total of 99 eyes (48 with wAMD, 51 with DME) were included in the analysis. The ICCs of the global RNFL thickness and global BMO-MRW measurements were 0.996 and 0.997, respectively, in wAMD and 0.994 and 0.996, respectively, in DME eyes. The CV values of global RNFL thickness and BMO-MRW were 0.60% and 0.73%, respectively, in wAMD eyes and 1.10% and 1.21%, respectively, in DME eyes. The disc membrane on the optic nerve head significantly affected global BMO-MRW repeatability (B = 0.814, p < 0.001).Conclusions: Both RNFL thickness and BMO-MRW measurements showed good repeatability in eyes with wAMD and DME. The severity of the optic disc membrane significantly affected the repeatability of BMO-MRW measurements in eyes with wAMD and DME. Therefore, physicians should examine the BMO-MRW in eyes with severe optic disc membrane.

Bringing the Ca 2+ sensitivity of myristoylated recoverin into the physiological range

The prototypical Ca 2+ -sensor protein recoverin (Rec) is thought to regulate the activity of rhodopsin kinase (GRK1) in photoreceptors by switching from a relaxed (R) disc membrane-bound conformation in the dark to a more compact, cytosol-diffusing tense (T) conformation upon cell illumination. However, the apparent affinity for Ca 2+ of its physiologically relevant form (myristoylated recoverin) is almost two orders of magnitude too low to support this mechanism in vivo . In this work, we compared the individual and synergistic roles of the myristic moiety, the GRK1 target and the disc membrane in modulating the calcium sensitivity of Rec. We show that the sole presence of the target or the disc membrane alone are not sufficient to achieve a physiological response to changes in intracellular [Ca 2+ ]. Instead, the simultaneous presence of GRK1 and membrane allows the T to R transition to occur in a physiological range of [Ca 2+ ] with high cooperativity via a conformational selection mechanism that drives the structural transitions of Rec in the presence of multiple ligands. Our conclusions may apply to other sensory transduction systems involving protein complexes and biological membranes.

Distinct roles for prominin-1 and photoreceptor cadherin in outer segment disc morphogenesis in CRISPR-altered X. laevis

Mutations in prominin-1 (prom1) and photoreceptor cadherin (cdhr1) are associated with inherited retinal degenerative disorders but their functions remain unknown. We used CRISPR-Cas9 to generate prom1-, cdhr1-, and prom1+cdhr1-null X. laevis and then documented the effects of these mutations on photoreceptor structure and function. Prom1-null mutations resulted in severely dysmorphic photoreceptors comprised of overgrown and disorganized disc membranes. Cone outer segments were more severely affected than rods and had an impaired ERG response. Cdhr1-null photoreceptors did not appear grossly dysmorphic, but ultrastructural analysis revealed that some disc membranes were overgrown or oriented vertically within the plasma membrane. Double-null mutants did not differ significantly from prom1-null mutants. Our results indicate that neither prom1 nor cdhr1 are necessary for outer segment disc membrane evagination or the fusion event that controls disc sealing. Rather, they are necessary for the higher-order organization of the outer segment. Prom1 may align and reinforce interactions between nascent disc leading edges, a function more critical in cones for structural support. Cdhr1 may secure discs in a horizontal orientation prior to fusion and regulate cone lamellae size.

Prediction of maximum permeate flux (%) of disc membrane using response surface methodology (RSM)

The paper investigates increasing permeate flux (%) of the disc membrane which can improve the quality of rubber industrial effluent of Tripura. Response surface methodology was used to optimize the independent influencing parameters to improve the permeate flux. The effect of different influencing parameters like operating pressure, membrane pore size, and inlet feed velocity on membrane permeate flux were studied to determine the optimum operating conditions within the predefined boundary. The experiments were pre-planned and designed according to central composite rotatable design, and second-order polynomial regression model was developed for regression and analysis of variance study. Results show the membrane has maximum permeate flux (%) when the operating pressure is 14.50 Pa, pore size is 0.20 μm, and inlet feed velocity is 2.10 m/s. The Pareto analysis in the study established that the inlet velocity was the most influential parameter in the model equation.

Implications of dimeric activation of PDE6 for rod phototransduction

We examine the implications of a recent report providing evidence that two transducins must bind to the rod phosphodiesterase to elicit significant hydrolytic activity. To predict the rod photoreceptor's electrical response, we use numerical simulation of the two-dimensional diffusional contact of interacting molecules at the surface of the disc membrane, and then we use the simulated PDE activity as the driving function for the downstream reaction cascade. The results account for a number of aspects of rod phototransduction that have previously been puzzling. For example, they explain the existence of a greater initial delay in rods than in cones. Furthermore, our analysis suggests that the ‘continuous’ noise recorded in rods in darkness is likely to arise from spontaneous activation of individual molecules of PDE at a rate of a few tens per second per rod, probably as a consequence of spontaneous activation of transducins at a rate of thousands per second per rod. Hence, the dimeric activation of PDE in rods provides immunity against spontaneous transducin activation, thereby reducing the continuous noise. Our analysis also provides a coherent quantitative explanation of the amplification underlying the single photon response. Overall, numerical analysis of the dimeric activation of PDE places rod phototransduction in a new light.