Elementary response triggered by transducin in retinal rods

G protein-coupled receptor (GPCR) signaling is crucial for many physiological processes. A signature of such pathways is high amplification, a concept originating from retinal rod phototransduction, whereby one photoactivated rhodopsin molecule (Rho*) was long reported to activate several hundred transducins (GT*s), each then activating a cGMP-phosphodiesterase catalytic subunit (GT*·PDE*). This high gain at the Rho*-to-GT* step has been challenged more recently, but estimates remain dispersed and rely on some nonintact rod measurements. With two independent approaches, one with an extremely inefficient mutant rhodopsin and the other with WT bleached rhodopsin, which has exceedingly weak constitutive activity in darkness, we obtained an estimate for the electrical effect from a single GT*·PDE* molecular complex in intact mouse rods. Comparing the single-GT*·PDE* effect to the WT single-photon response, both in Gcaps−/− background, gives an effective gain of only ∼12–14 GT*·PDE*s produced per Rho*. Our findings have finally dispelled the entrenched concept of very high gain at the receptor-to-G protein/effector step in GPCR systems.

Non-axisymmetric and/or non-elementary response of anisotropic tuff in axisymmetric, elementary triaxial test

Specimens of triaxial tests ordinarily response as element in the axisymmetric condition, and it is theoretically correct assumption. However, for anisotropic rocks, the axisymmetric condition is not always satisfied because incremental relationships between stresses and strains are not coaxial. In addition, such rock specimen often shows non-uniform deformation behaviors due to end frictions. As the reason, the influence of end restraints on deformation behaviors of anisotropic rocks during triaxial compression is much greater than that of isotropic one. In this study, the variations in the stress-strain relationships of anisotropic tuff due to the condition of end restraints are investigated. The results of four consolidated drained triaxial tests with measuring the strain tensor demonstrated that the axial and volumetric strains were not influenced by whether sliding mechanism and Teflon sheets are installed at the end of specimens or not; meanwhile, the shear components of the strain tensor and the inclinations of principal strain orientations are widely varied owing to the end restraints.

Light Adaptation in Drosophila Photoreceptors

It is known that an increase in both the mean light intensity and temperature can speed up photoreceptor signals, but it is not known whether a simultaneous increase of these physical factors enhances information capacity or leads to coding errors. We studied the voltage responses of light-adapted Drosophila photoreceptors in vivo from 15 to 30°C, and found that an increase in temperature accelerated both the phototransduction cascade and photoreceptor membrane dynamics, broadening the bandwidth of reliable signaling with an effective Q10 for information capacity of 6.5. The increased fidelity and reliability of the voltage responses was a result of four factors: (1) an increased rate of elementary response, i.e., quantum bump production; (2) a temperature-dependent acceleration of the early phototransduction reactions causing a quicker and narrower dispersion of bump latencies; (3) a relatively temperature-insensitive light-adapted bump waveform; and (4) a decrease in the time constant of the light-adapted photoreceptor membrane, whose filtering matched the dynamic properties of the phototransduction noise. Because faster neural processing allows faster behavioral responses, this improved performance of Drosophila photoreceptors suggests that a suitably high body temperature offers significant advantages in visual performance.