Control of membrane N+ permeability in a hyperpolarizing photoreceptor: similar effect of light and metabolic inhibitors

In the hyperpolarizing photoreceptors of the scallop Pecten irradians the metabolic inhibitors cyani 'e and 2,4-dinitrophenol cause a rapid hyperpolarization and increase in membrane permeability to potassium ions, similar to the effect of light. Cellular metabolism appears important in maintaining the low permeability to potassium ions necessary to keep the membrane depolarized in darkness, possibly by regulating the intracellular calcium ion concentration.     

Divalent cations directly affect the conductance of excised patches of rod photoreceptor membrane

Phototransduction in rod cells is likely to involve an intracellular messenger system that links the absorption of light by rhodopsin to a change in membrane conductance. The direct effect of guanosine 3',5'-monophosphate (cGMP) on excised patches of rod outer segment membrane strongly supports a role for cGMP as an intracellular messenger in phototransduction. It is reported here that magnesium and calcium directly affect the conductance of excised patches of rod membrane in the absence of cGMP and that magnesium, applied to intact rod cells, blocks a component of the cellular light response. The divalent cation-suppressed conductance in excised patches showed outward rectification and cation-selective permeability resembling those of the light-suppressed conductance measured from the intact rod cell. The divalent cation-suppressed conductance was partly blocked by a concentration of the pharmacological agent L-cis-diltiazem that blocked all of the cGMP-activated conductance. Divalent cations may act, together with cGMP, as an intracellular messenger system that mediates the light response of the rod photoreceptor cell.     

Cyclic nucleotide phosphodiesterase: high activity in a mammalian photoreceptor

Purified outer segments of bovine rods exhibit phosphodiesterase activity against adenosine and guanosine cyclic 3',5'-monophosphates (cyclic AMP and cyclic GMP). The enzyme hydrolyzed cyclic GMP more rapidly than cyclic AMP at low substrate concentrations. The presence of high phosphodiesterase activity in this highly specialized organelle suggests that this enzyme may function in control of cyclic nucleotide concentration during visual excitation or adaptation.     

Photoreception in a barnacle: electrophysiology of the shadow reflex pathway in Balanus cariosus

The photoreceptors in the median ocellus of the rock barnacle depolarize when illuminated. This depolarization spreads passively to the axon terminals in the supraesophageal ganglion. A small number of cells in the supraesophageal ganglion hyperpolarize when the median ocellus is illuminated and depolarize when it is shadowed. Nerve impulses are superimposed on the slow depolarization of the ganglion cells. Impulse activity in response to shadowing the median ocellus is recorded in a few fibers of the circumesophageal connectives. Picrotoxin blocks this shadow-induced activity. A model of the shadow reflex pathway is presented.     

鳜视觉转变期视网膜感光细胞层的发育

为研究鳜Siniperca chuatsi视觉转变期视网膜感光细胞层结构变化,利用组织切片、免疫荧光技术与几何构型分析对鳜视觉转变期3个阶段(出膜后第28、42、63天,记为D28、D42和D63)视网膜中感光细胞数量增长方式和视锥细胞排布进行了研究.结果表明:鳜视觉转变期视网膜各区域视杆细胞数量显著增加,D63时期已...     

鳜视觉转变期视网膜感光细胞层的发育

为研究鳜Siniperca chuatsi视觉转变期视网膜感光细胞层结构变化,利用组织切片、免疫荧光技术与几何构型分析对鳜视觉转变期3个阶段(出膜后第28、42、63天,记为D_(28)、D_(42)和D_(63))视网膜中感光细胞数量增长方式和视锥细胞排布进行了研究。结果表明:鳜视觉转变期视网膜各区域视杆细胞数量显著增加,D_(63)时期已达4 500～6 000 cells/100μm~2;单锥细胞(SC)数量上升缓慢,D_(28)时期为20～40 cells/100μm~2,而D_(63)时为5～8 cells/100μm~2,同时双锥细胞(DC)数量增长速度明显快于单锥细胞,D_(28)时期为70～100 cells/100μm~2,而D_(63)时期为100～150 cells/100μm~2,视锥细胞中双锥细胞比例显著上升,D_(63)时期DC/SC已接近50;视锥细胞在视网膜腹侧的增长均快于背侧,而增长的视杆细胞未影响视锥细胞排布的构建。研究表明,鳜视觉转变期视网膜感光细胞层在结构上发生了剧烈变化,视杆细胞在视网膜各区域均匀增长,视锥细胞腹侧增长速度明显快于背侧,鳜感光细胞发育特点为其底栖暗光生活的视觉转变提供了结构基础。     

鳜视觉转变期视网膜感光细胞层的发育

为研究鳜Siniperca chuatsi视觉转变期视网膜感光细胞层结构变化,利用组织切片、免疫荧光技术与几何构型分析对鳜视觉转变期3个阶段(出膜后第28、42、63天,记为D_(28)、D_(42)和D_(63))视网膜中感光细胞数量增长方式和视锥细胞排布进行了研究。结果表明:鳜视觉转变期视网膜各区域视杆细胞数量显著增加,D_(63)时期已达4 500～6 000 cells/100μm²;单锥细胞(SC)数量上升缓慢,D_(28)时期为20～40 cells/100μm2;单锥细胞(SC)数量上升缓慢,D_(28)时期为20～40 cells/100μm²,而D_(63)时为5～8 cells/100μm2,而D_(63)时为5～8 cells/100μm²,同时双锥细胞(DC)数量增长速度明显快于单锥细胞,D_(28)时期为70～100 cells/100μm2,同时双锥细胞(DC)数量增长速度明显快于单锥细胞,D_(28)时期为70～100 cells/100μm²,而D_(63)时期为100～150 cells/100μm2,而D_(63)时期为100～150 cells/100μm²,视锥细胞中双锥细胞比例显著上升,D_(63)时期DC/SC已接近50;视锥细胞在视网膜腹侧的增长均快于背侧,而增长的视杆细胞未影响视锥细胞排布的构建。研究表明,鳜视觉转变期视网膜感光细胞层在结构上发生了剧烈变化,视杆细胞在视网膜各区域均匀增长,视锥细胞腹侧增长速度明显快于背侧,鳜感光细胞发育特点为其底栖暗光生活的视觉转变提供了结构基础。     

Asymmetric illumination contrast: a method of image formation for video light microscopy

Images with high resolution and exceptionally broad gray scale can be obtained by the application of video contrast enhancement to an optimized procedure for imaging transparent objects with oblique rays of illumination. This technique is simple to set up. A conventional microscope with a light source whose position can be adjusted and a video camera with controls for gain and black level are the only essential components. Features such as high resolution, optical sectioning, control of contrast, and operation under low light intensity make this technique preferable, in several instances, to currently used video microscopy techniques.     

Methoxyindoles and photoreceptor metabolism: activation of rod shedding

Using an in vitro eye-cup preparation, we have evaluated a potential relationship between methoxyindole metabolism and photoreceptor disk shedding. Melatonin, 6-chloromelatonin, and 5-methoxytryptophol all activate rod disk shedding in culture. The effect is compound specific since serotonin and N-acetylserotonin are without effect, and it is similar to shedding in vivo because it is evoked by light and is quantitatively comparable to a normal intact animal response. The results suggest the involvement of 5-methoxyindoles in the control of rhythmic photoreceptor metabolism.     

Permeability of a nuclear membrane: changes during normal development and changes induced by growth hormone

The ion permeability of the nuclear membrane envelope of salivary gland cells (of the midge Chironomus thummi) undergoes changes during development. Following the early fourth instar stage, permeability falls to about one-fifth of its base value over a period of 3 to 5 days of development of the animal, and then rises again over the next 2 to 4 days. The falling phase of the change can be reproduced within 1 hour by injections of the growth hormone ecdyson.     

Response of the pupil to steady-state retinal illumination: contribution by cones

Response of the pupil to steady-state retinal illumination was measured in an observer who lacked functioning rods. At high intensities, this response was as great as that of a normal eye. These results cannot be explained by the hypothesis that only rods are receptors for the steady-state response.     

Geophysicists in moscow: signs of easier relations

Science editor Philip H. Abelson attended the 15th general assembly of the International Union of Geodesy and Geophysics in Moscow on 1 through 14 August. There he served as principal U.S. delegate to the International Association of Volcanology and Chemistry of the Earth's Interior. In preparing the following notes for publication, he checked his own impressions extensively against those of American scientists who participated in other sections of the meeting, and against the impressions of those who visited scientific institutions in the Moscow region.     

Clathrin: a role in the intracellular retention of a Golgi membrane protein

Yeast mutants deficient in the clathrin heavy chain secrete a precursor form of the alpha-factor, a peptide-mating pheromone. Analysis of this defect indicates that the endoprotease Kex2p, which is responsible for initiating proteolytic maturation of the alpha-factor precursor in the Golgi apparatus, is unexpectedly present at the plasma membrane in mutant cells. This result suggest that clathrin is required for the retention of Kex2p in the Golgi apparatus.     

Long-chain diols: a new class of membrane lipids from a thermophilic bacterium

Glycerol-derived membrane lipids are essentially absent in the thermophilic bacterium Thermomicrobium roseum. A series of straight chain and internally methyl-branched 1,2-diols of carbon numbers C(18) to C(23) were found to replace glycerolipids in this bacterium. Fatty acids were present but were ester-linked to the diols or amide-linked to polar heads groups and not to glycerol. This thermophile has evolved the integration of diols as a novel approach for the construction of its cytoplasmic membrane.     

Circadian rhythm of cell division in Euglena: effects of random illumination regimen

A persisting, "free-running," circadian rhythm of cell division in autotrophically grown Euglena gracilis is obtained upon placing either an exponentially increasing population or a culture that has been synchronized by a 10:14 light-dark cycle in a random illumination regimen that affords a total of 8 hours of light each 24 hours. These results are interpreted as implicating an endogenous biological clock which "gates" the specific event of cell division in the cell developmental cycle.     

Salicylate: a structure-activity study of its effects on membrane permeability

Salicylate atnd benzoate, and their anlalogs, reversibly increase the membrane potetntial and conductance of identified molluscan neurons by increasing potassium conductance and decreasing chloride conductance. The relative potencies of these compounds were closely correlated with their octanol-water partition coefficients and their pK(a) values.