The action of phosphodiesterase inhibitors on the hypersensitivity of frog photoreceptor

The increase in sensitivity of frog photoreceptors after illumination, "hypersensitivity", was studied by recording fast-PIII responses of the isolated bull frog retina superfused with physiological saline containing 5 mM sodium aspartate. The hypersensitivity is mot marked after illumination which bleaches only 0.01% of the rhodopsin initially present. The wavelength of light, which is optimum to induce the hypersensitivity, is about 500 nm. Several kinds of phosphodiesterase inhibitors, isobutylmethylxanthine (IBMX), papaverine, theophylline and caffeine act to induce the hypersensitivity, as does lowered extracellular concentrations of calcium ion, [Ca2+]out. Such action of phosphodiesterase inhibitor can be antagonized by an increase in [Ca2+]out. The relation between effects of Ca2+ and cyclic nucleotides on photoreceptor is discussed.

Effect of leaf extracts of Aloe arborescens Mill subsp. natalensis Berger on growth of Trichophyton mentagrophytes

The antifungal activity of a lyophilized powder containing aloe leaf homogenate (whole-leaf powder) against Trichophyton mentagrophytes was investigated. The minimal inhibitory concentration was 25 mg/ml by the agar dilution method, using Sabouraud glucose agar medium. At subinhibitory concentrations, the powder exerted its main effect on colony growth by prolongation of the lag phase and inhibition of growth rate. Homogenates of fresh whole leaf were filtered through Whatman GF/A paper, and the filtrate was dialyzed and concentrated by molecular filtration using an Amicon hollow-fiber dialyzer concentrator DC-2, and a powder containing components with molecular weights higher than 10,000 (high-molecular-weight component powder) was prepared by lyophilization. The minimal inhibitory concentrations against three strains of T. mentagrophytes were all 10 mg/ml. The inhibitory activity was fungicidal and was lost by heating at 100 degrees C for 30 min. Both the whole-leaf powder and the high-molecular-weight component powder induced various morphological abnormalities in spores and hyphae by the inhibition of spore germination and development of hyphae.

Regeneration of rhodopsin in frog rod outer segments

1. Bleaching/regeneration cycles were performed in perfused frog retina while the optical transmittance at suitable wave-lengths was measured continously. Rhodopsin was identified from its spectral absorbance, its photosensitivity and from the kinetics of its regeneration. 2. In the absence of the pigment epithelium regeneration was complete when not more than 2-5% of the rhodopsin initially present had been bleached. However, the cycles could be repeated to a total of regenerated rhodopsin exceeding that explicable on the utilization of stored chromophores. The rate of regeneration was fast, with 0-12 min-1 rate constant, following first order reaction kinetics. Under these conditions the cycle does not seem to involve stages beyond metarhodopsin II. With the moderate bleaching intensities used, half-time 53 min, the Bunsen-Roscoe law was obeyed up to 15 min, indicating a capacity for the photoproducts to be accomondated in situ for subsequent regeneration. 3. It is concluded that only substantial bleaches, which exceed that capacity, result in hydrolysed chromophores. These surplus chromophores become esterified and are temporarily taken up by the pigment epithelium to be re-entered into the visual cycle as fast as they can be processed by the regenerative machinery of the rod outer segments.

Evaluation of the in vitro antifungal activity of allicin

Allicin was effective in vitro against Candida, Cryptococcus, Trichophyton, Epidermophyton, and Microsporum. The minimal inhibitory concentrations (MICs) of allicin against these organisms were 3.13 to 6.25 mug/ml by the agar dilution method and 1.57 to 6.25 mug/ml by the broth dilution method, using Sabouraud glucose (SG) medium. However decreased activity was demonstrated against Aspergillus. The MIC of allicin against various pathogenic fungi was affected considerably by differences in the experimental conditions, e.g., incubation time, inoculum size, type of medium, and medium pH. The MIC of allicin against Candida, Cryptococcus, and Aspergillus remained constant after more than 3 days of incubation, and that against Dermatophytes remained constant after more than 10 days of incubation. Decreasing the inoculum size increased the susceptibility to allicin. The antifungal activity of allicin was stronger on SG agar medium with a pH of 5.6 than on the same medium with a pH of 6.0 or higher. By microscopical observation, allicin induced morphological abnormalities in hyphae of Trichophyton mentagrophytes Morita. Percent germination of spores of the Morita strain at 24 h in SG agar medium was greatly decreased with an allicin concentration of 3.13 mug/ml, and the lethal dose for the spores was about four times higher than the fungistatic concentration. These results suggest that allicin inhibits both germination of spores and growth of hyphae.

Circular dichroism of cephalopod rhodopsin and its intermediates in the bleaching and photoregeneration process

In the bleaching process of cephalopod rhodopsin, a new intermediate was found in the conversion process from lumirhodopsin to metarhodopsin. This intermediate of octopus has an absorption peak at about 475 nm and has been named as M475. The circular dichroism value of M475 is too small to be evaluated. On the other hand, lumirhodopsin shows a negative CD at 470 nm, a positive CD at 350 nm and a large positive CD band with three peaks at 280, 287 and 295 nm. Such a large CD band in the ultraviolet region is not observed in rhodopsin, M475 and metarhodopsin. This CD seems to be mainly due to tryptophan and tyrosine residues restricted in free rotation in the protein moiety of lumirhodopsin. The intermediate in the photoregeneration process of cephalopod rhodopsin, P380, has a positive CD band at the main peak, 380 nm, and also a large positive CD band in the ultraviolet region like lumirhodopsin.