Light induces a rapid increase in cAMP and activates PKA in rod outer segments of the frog retina.

The phototransduction cascade enables the photoreceptor to detect light over a wide range of intensities without saturation. The main second messenger of the cascade is cGMP and the primary regulatory mechanism is calcium feedback. However, some experimental data suggest that cAMP may also play a role in regulating the phototransduction cascade, but this would require changes in cAMP on a time scale of seconds.

The RhoA regulators Myo9b and GEF-H1 are targets of cyclic nucleotide-dependent kinases in platelets.

Background: Circulating platelets are maintained in an inactive state by the endothelial lining of the vasculature. Endothelium-derived prostacyclin and nitric oxide stimulate cAMP- and cGMP-dependent kinases, PKA and PKG, to inhibit platelets. PKA and PKG effects include the inhibition of the GTPase RhoA, which has been suggested to involve the direct phosphorylation of RhoA on serine 188.

Elevated cAMP improves signal-to-noise ratio in amphibian rod photoreceptors.

The absolute sensitivity of vertebrate retinas is set by a background noise, called dark noise, which originates from several different cell types and is generated by different molecular mechanisms. The major share of dark noise is produced by photoreceptors and consists of two components, discrete and continuous. Discrete noise is generated by spontaneous thermal activations of visual pigment.

Efficacy of green tea extract in two exercise models.

Oral administration of green tea extract in a dose of 6 mg/kg twice a day (before and after exercise) over 2 weeks significantly increased swimming times on week 1 and 2 in comparison with control animals receiving water. The 7-day and final exhaustive running in rats was accompanied by a significant decrease in spleen weight and iron serum levels associated with developed reticulocytosis. Administration of green tea extract in a dose of 12 mg/kg once a day (before exercise) for 2 weeks did not affect the duration of the running, but prevented the decrease in serum iron and spleen weight, that, along with a significantly increased concentration of reduced glutathione in erythrocytes, can indicate a normalizing effect of green tea extract on hemopoiesis and stimulating effect on the antioxidant system of erythrocytes.

Rhodopsin, Zn(2+), and retinitis pigmentosa: a short tale requiring continuation.

Understanding the relationship between the visual pigment rhodopsin and Zn2+ under normal conditions and in case of deficiency of the latter, as well as the realization of the role of Zn2+ in the development of the hereditary disease retinitis pigmentosa, have great theoretical and practical importance. In this mini-review, we briefly examine the basic experimental data on the role of Zn2+ in the retina and photoreceptors, binding of endogenous Zn2+ by zinc-binding sites of differing affinities in rhodopsin, the influence of the exogenous Zn2+ on various properties of rhodopsin, including its ability for phosphorylation and activation of transducin, as well as its thermal stability and regeneration. Conflicting results on the correlation between Zn2+ content in the blood serum and the development of retinitis pigmentosa in patients are demonstrated.

Proof of oligomeric state of frog rhodopsin: visualization of dimer and oligomers on gels after BN- and HRCN-PAGE using antibodies to rhodopsin and by retinylopsin fluorescence.

Staining by antibodies to rhodopsin (Rh) and fluorescence of N-retinylopsin (RO) have shown that digitonin (DIG)- , dodecyl-β-D-maltoside (DM)- , and sodium dodecyl sulfate (SDS)-solubilized frog Rh after BN- and HRCN-PAGE is situated in the gradient gel in the state of dimer with a slight content of higher oligomers (trimer, tetramer, etc.). With increasing detergent harshness (DIG < DM < SDS), the proportion of higher oligomers in extracts becomes more prominent.

Aggregation of frog rhodopsin to oligomers and their dissociation to monomer: application of BN- and SDS-PAGE.

After solubilization of frog rod outer segments (ROS) with mild detergents (digitonin, n-dodecyl-beta-D-maltoside, Chaps, Triton X-100) and subsequent one-dimensional blue native polyacrylamide gel electrophoresis (1D BN-PAGE), the position of rhodopsin (Rh) on the gradient gel does not match the monomer with molecular weight of 40 kDa but appears self-associated into aggregate of Rh (RhA) with molecular mass varying in different detergents from 85 to 125 kDa. Short-term treatment (~2 h) of the excised BN-PAGE strip containing RhA by denaturing detergent mixture (10% SDS + 1 mM dithiothreitol (DTT)) followed by 2D SDS-PAGE revealed dissociation of the RhA into opsin monomer and unidentified proteins. Long-term treatment (approximately 2 days) of RhA that included extraction, denaturation, concentration, and electrophoresis induced, along with dissociation of RhA into opsin monomer + unidentified proteins, also formation of opsin dimers, trimers, and higher oligomers owing to a secondary aggregation of opsin.