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Biomedical subjects

P P Zak

Publications and source records attributed to P P Zak.

At least 19 recordsLinked to original sources
PubMed2001

Ionochromic properties of long-wave-sensitive cones in the goldfish retina: an electrophysiological and microspectrophotometric study.

Long-wave-sensitive (LWS) cone visual pigments are sensitive to the concentration of chloride ions and show a spectral shift to shorter wavelengths when exposed to low chloride levels. We have used the aspartate-isolated mass receptor potential of the electroretinogram (ERG) to establish whether the spectrally shifted cone pigment is functional. In the goldfish, Carassius auratus, the lambda(max) of the LWS porphyropsin is displaced from about 622 nm to around 606 nm when chloride is replaced by gluconate. The electrical response of the LWS cones (but not MWS cones and rods) is selectively and reversibly abolished by the removal of chloride ions. The effect is concentration dependent and a decrease to half the normal chloride ion concentration is sufficient to cause a decrease in the response.

Animals↗
PubMed2001

[High resistance of the rat retina rods to hypoxia].

The amplitude of photoreceptor potential was shown to be constant in hypoxia. Under this condition, the energy support of the photoreceptor potential seems to be realized through an anaerobic process rather than the oxidative phosphorylation. The effect of hypoxia was shown to manifest itself in a decrease of the sagged peak part of the photoreceptor potential occurring in response to bright flashes. Such changes of wave form are typical for the case when the rod intracellular potential decreases. The decrease of response amplitude to bright flashes shortens the light scale of the amplitude/light intensity curve.

Animals↗
PubMed2000

Spectral filters in low-vision correction.

Coloured filters are used to protect the lens, retina and other ocular tissues against the hazard of light damage and to improve the quality of vision mainly in cases of ocular media opacities. Four types of yellow, amber and orange filters have been designed as tinted glasses, shields and colour covering of spectacles. They were tested on 15 adult patients with partial cataract and on 80 children with congenital pathology (i.e. macular hypoplasia, albinism, aphakia after congenital cataract). The majority of the children had nystagmus. The filters with particular spectral characteristics provide reduction of light intensity in the light-damaging range by at least a factor of five. Optimal filters were selected by examination of visual acuity, contrast frequency sensitivity, glare sensitivity and subjective selection by the patients. The effects of filters were: 11-43% increase in corrected visual acuity, 27-34% increase in contrast sensitivity function (CSF) for all frequencies and a marked reduction in glare sensitivity. All patients reported subjective improvement including reduction of photophobia, eye-strain and eye discomfort. It is concluded that coloured filters are able to contribute substantially to rehabilitation of low-vision patients.

Adolescent↗
PubMed1989

[The effect of anions on spectral properties of iodopsin and native cones in the frog retina (microspectrophotometric study)].

Absorption spectra of single outer segments of the frog Rana temporaria photoreceptors were registered. Effects of nitrate and chloride ions on spectral properties of cone and rod pigments were compared. These pigments proved to differ in structure of the native photoreceptor membrane and, therefore, in effect of hydrophile environment on the chromophore centrum. Substitution of chloride by nitrate ions led to the hypochromic shift of the cone absorption spectrum (20-25 nm) but does not affect the spectrum on case of rod pigment. The ionochromic behaviour of cone pigments resembles that of the light-sensitive halobacterium protein halorhodopsin, in native membrane. We suppose that the effect of anions on the chromophore centrum may be the cause of bathochromic shifts of absorption spectra of longwave-length retinal-containing pigments.

Animals↗
PubMed1987

[Aggravating action of oxygen in light injury to the retina in the white rat].

Rhodopsin concentration and "a"-wave ERG decrease, depending on illumination in the range of 360-380 nm have been investigated in albino rats. The dose of 1.8 J/cm2 proved sufficient for a decrease of "a"-wave ERG by 70% and for the reduction in rhodopsin concentration by 80%. The substitution of the air for O2 (1 or 2.5 ata) resulted in a considerable increase of photodamage of the retina.

Air Pressure↗
PubMed1985

[Participation of cyclic nucleotides and calcium in regulation of the sensitivity of vertebrate photoreceptors].

Effects of PDE inhibitor IBMX and of Ca2+ decrease upon sensitivity of rods and cones were compared. IBMX greatly increases the sensitivity of rods but not that of cones. Ca2+ does not significantly affect the sensitivity of both rods and cones. Possible role of cyclic nucleotides as feed--back regulator in mechanisms of photoreception is discussed.

1-Methyl-3-isobutylxanthine↗
PubMed1978

[ATP regeneration in the outer segments of frog photoreceptors].

The outer segments of retinal photoreceptors of the frog Rana temporaria were found to possess the adenylate kinase and creatine phosphokinase activities. It was shown that the activities found are not due to contaminations by the fragments of inner photoreceptor segments and pigment epithelium processes which are in direct contact with outer segments. The absolute value of the ATP resynthesis rate exceeds the rate of its hydrolysis. It is concluded that ATP synthesis in the creatine phosphokinase and adenylate kinase reactions is one of the pathways of ATP regeneration in vivo.

Adenosine Triphosphatases↗
PubMed1975

[The effect of acetylcholine on the membrane potential of goldfish retina horizontal cells and the frog electroretinogram].

The effect of acetylcholine was studied as applied to horizontal cells of the goldfish retina and frog electroretinogram ACh (1-10-9--1-10-3 M) depolarized the cells. The highest level of depolarization never reached the O-level of the membrane potential and was approximately equal to the membrane potential in the dark. ACh (1-10-2--5-10-2 M) inhibited b- and d-waves and revealed the stable PIII component. It is supposed that ACh may be a transmitter in retinal outer synpatic layer.

Acetylcholine↗
PubMedDate not supplied

[Increase in visual acuity in poorly-sighted patients by using spectral filters].

Tinted eyeglasses were selected for 768 poor-sighted patients aged 5-86 years with various ocular diseases. The frequency of tinted glasses utilization by poor-sighted patients was as follows: filter O2 was the optimal for 38% patients, filters G2 and K4 for 16-18%, and G1 for 11% patients. Filter G1 improved visual acuity by 19%, filters G2 and K4-K5 by 23%; the highest increment of visual acuity was observed with O2 filter: by 27%. Filters of different spectral characteristics and density may be useful in the same underlying ophthalmic disease, which is explained by the underlying disease and the presence, combinations, and severity of concomitant ocular diseases.

Eyeglasses↗