PubMed Health⌕ Search

Biomedical subjects

S E Ostroy

Publications and source records attributed to S E Ostroy.

9 recordsLinked to original sources
PubMed1992

Extracellular glucose dependence of rhodopsin regeneration in the excised mouse eye.

To study the process of rhodopsin regeneration a superfused excised whole eye preparation of the albino mouse was developed. With this preparation, complete regeneration could be observed after each of the first two illuminations (bleaching 15-20%), and incomplete regeneration after a third illumination. Regeneration was minimal at extracellular glucose concentrations of 0 or 1 mM with improved regenerations at higher concentrations. Maximum regenerations were observed at glucose concentrations of 4-10 mM. First-bleach regenerations were as follows: 0 mM glucose, 20%; 1 mM, 8%; 2 mM, 45%; 3 mM, 82%; 4 mM, 115%; 5.1 mM, 121%; 7 mM, 120%; and 10 mM, 126%. The effects of reduced glucose were reversible. After an initial bleach with 0 or 1 mM extracellular glucose that exhibited minimal regeneration, the re-addition of glucose (5.1 mM) restored the ability of the eye to regenerate rhodopsin following a second bleach, but only to the level prior to that bleach. Mitochondrial substrates fumarate (10 mM) or pyruvate (10 mM) partly substituted for glucose, exhibiting first-bleach regenerations of 56 and 85%, respectively.

Animals↗
PubMed1990

A stage in glycolysis controls the metabolic adjustments of vertebrate rod photoreceptors upon illumination.

The factors affecting the metabolic adjustments of toad rod photoreceptors were studied by monitoring the oxygen utilization of excised retinas and by measuring rod outer segment ATP and GTP concentrations. Respiratory adjustments upon illumination were observed when glucose or fructose was provided in the perfusate, but not when a glycolytic inhibitor was added to the perfusate containing glucose and pyruvate, or when a substrate beyond glycolysis or from a later stage of glycolysis was substituted for glucose. The amplitudes of the respiratory adjustments to illumination were dependent on the concentration of glucose in the perfusate. The ATP and GTP concentration changes were dependent on respiratory adjustments, including glycolytic effects, and on the levels of illumination. The data suggest a control point within glycolysis for light-induced adjustments of respiration, possibly at phosphofructokinase.

Adenosine Triphosphate↗
PubMed1979

Renewal of opsin in the photoreceptor cells of the mosquito.

Mosquito rhodopsin is a digitonin-soluble membrane protein of molecular weight 39,000 daltons, as determined by sodium dodecyl sulfate gel electrophoresis. The rhodopsin undergoes a spectral transition from R515-520 to M480 after orange illumination. The visual pigment apoprotein, opsin, is the major membrane protein in the eye. Protein synthesis in the photoreceptor cells occurs in the perinuclear cytoplasm and the newly made protein is transported to the rhabdom. Light adaptation increases the rate of turnover of this rhabdomal protein. The turnover of electrophoretically isolated opsin is also stimulated by light adaptation. The changes observed in protein metabolism biochemically, are consistent with previous morphological observations of photoreceptor membrane turnover. The results agree with the hypothesis that the newly synthesized rhabdomal protein is opsin.

Adaptation, Physiological↗
PubMed1978

Ionizable groups and conductances of the rod photoreceptor membrane.

The ionizable groups and conductances of the rod plasma membrane were studied by measuring membrane potential and input impedance with micropipettes that were placed in the rod outer segments. Reduction of the pH from 8.0 to 6.8 or from 7.8 to 7.3 resulted in membrane depolarization in the dark from 8.0 to 6.8 or from 7.8 to 7.3 resulted in membrane depolarization in the dark (by 2- 3 mV) and an increased size of the light response (also by 2-3 mV). The dark depolarization was accompanied by and increased resting input impedance (by 11-35 Momega). When the pH was decreased in a perfusate in which Cl(-) was replaced by isethionate, the membrane depolarized. When the pH was decreased in a perfusate in which Na(+) was replaced by choline, an increase of input impedance was observed (11-50 Momega) even though a depolarization did not occur. These results are consistent with the interpretation that the effects of decreased extracellular pH result mainly from a decrease in rod membrane K(+) conductance that is presumably cause by protonation of ionizable groups having a pK(a) between 7.3 and 7.8. Furthermore, from these results and results obtained by using CO(2) and NH(3) to affect specifically the internal pH of the cell, it seems unlikely that altered cytoplasmic [H(+)] is a cytoplasmic messenger for excitation of the rod. When the rods were exposed to perfusate in which Na(+) was replaced by choline, the resting (dark) input impedance increased (by 26 Momega +/- 5 Momega SE), and the light-induced changes in input impedance became undetectable. Replacement of Cl(-) by isethionate had no detectable effect on either the resting input impedance or the light-induced changes in input impedance. These results confirm previous findings that the primary effect of light is to decrease the membrane conductance to Na(+) and show that, if any other changes in conductance occur, they depend upon the change in Na(+) conductance. The results are consistent with the following relative resting conductances of the rod membrane: G(Na(+)) similar to G(K(+)) more than 2-5 G(Cl(-)).

Ambystoma↗
PubMed1978

Characteristics of Drosophila rhodopsin in wild-type and norpA vision transduction mutants.

The properties of the major visual pigment of Drosophila melanogaster were evaluated. The visual pigment was isolated from other protein components using acrylamide gel electrophoresis and spectral identification. Sodium dodecyl sulfate (SDS) acrylamide gels of the isolated visual pigment gave a single protein subunit with a mol wt of 37,000 daltons. The rhodopsin480 molar extinction coefficient was 35,000 liter/mol-cm (+/- 2,700 SE). The metarhodopsin580 molar extinction coefficient was approximately 56,000 liter/mol-cm. Microspectrophotometry was used to compare the rhodopsin concentrations in wild-type flies and norpA vision transduction mutants. At 2 days of age (12 h dark-12 h light cycle, 19 degrees C) all of the norpA flies exhibited a similar rhodopsin concentration (75% of the wild-type strain). By 21 days of age some of the norpA alleles showed substantially reduced rhodopsin concentrations (16-43% of normal), whereas others showed no major age-dependent decreases (68-77%). Temperature and light-dark cycle affected the reduction. Alleles with no receptor potential exhibited the largest decreases in rhodopsin concentration. The data indicate that the norpA phototransduction mutant has a defect in the system responsible for maintaining the rhodopsin480 concentration. This defect in the rhodopsin maintenance system does not appear to be the cause of the reduced electroretinogram (ERG) amplitude observed in some of these mutants, but instead is a consequence of the decrease in ERG amplitude, or the flaw(s) responsible for the decrease in ERG amplitude.

Age Factors↗
PubMed1977

Electrical and adaptive properties of rod photoreceptors in Bufo marinus. I. Effects of altered extracellular Ca2+ levels.

The effects of altering extracellular Ca(2+) levels on the electrical and adaptive properties of toad rods have been examined. The retina was continually superfused in control (1.6 mM Ca(2+)) or test ringer's solutions, and rod electrical activity was recorded intracellularly. Low-calcium ringer's (10(-9)M Ca(2+)) superfused for up to 6 min caused a substantial depolarization of the resting membrane potential, an increase in light-evoked response amplitudes, and a change in the waveform of the light-evoked responses. High Ca(2+) ringer's (3.2 mM) hyperpolarized the cell membrane and decreased response amplitudes. However, under conditions of either low or high Ca(2+) superfusion for up to 6 min, in both dark-adapted and partially light-adapted states, receptor sensitivity was virtually unaffected; i.e., the V-log I curve for the receptor potential was always located on the intensity scale at a position predicted by the prevailing light level, not by Ca(2+) concentration. Thus, we speculate that cytosol Ca(2+) concentration is capable of regulating membrane potential levels and light-evoked response amplitudes, but not the major component of rod sensitivity. Low Ca(2+) ringer's also shortened the period of receptor response saturation after a bright but nonbleaching light flash, hence accelerating the onset of both membrane potential and sensitivity recovery during dark adaptation. Exposure of the retina to low Ca(2+) (10(-9)M) ringer's for long periods (7-15 min) caused dark-adapted rods to lose responsiveness. Response amplitudes gradually decreased, and the rods became desensitized. These severe conditions of low Ca(2+) caused changes in the dark-adapted rod that mimic those observed in rods during light adaptation. We suggest that loss of receptor sensitivity during prolonged exposure to low Ca(2+) ringer's results from a decrease of intracellular (intradisk) stores of Ca(2+); i.e., less Ca(2+) is thereby released per quantum catch.

Adaptation, Ocular↗