Psychophysical evidence for losses in rod sensitivity in the aging visual system.

Rod sensitivity was measured with a criterion-free psychophysical method at 10 deg in the horizontal meridian of the nasal field of the left eye on 26 young (mean age, 24.1 yr) and 14 older (mean age 72.6 yr) observers in good ocular health. A 1 deg, 90 msec stimulus was delivered by means of a free-viewing optical system under computer control. Stimulus wavelengths were chosen to have either significant (406 nm) or minimal (560 nm) absorption by the older lens. After correction for senile miosis and lens density, 0.39 log unit higher thresholds for the older observers remained and are interpreted as being due to neural factors.

Photophobia in patients with traumatic brain injury: Uses of light-filtering lenses to enhance contrast sensitivity and reading rate.

Patients who have sustained traumatic brain injury (TBI) often experience a new, intense and chronic photophobia. Photophobia, an intolerance to light, is an incompletely understood, subjective symptom, which has been divided into ocular and central types. Various commercial sources of light-filtering lenses have been developed, which have proven to be successful in diminishing visual symptoms expressed by patients who are photophobic. However, despite the many subjective reports of improved visual performance and comfort with use of these filters, there has been little documentation of actual enhanced visual sensitivity/efficiency. Letter contrast sensitivity (CS) and reading rate were measured in patients with TBI, who, despite good ocular health, experienced significant light intolerance. These patients exhibited up to two fold increases (0.3 log units) in binocular letter contrast sensitivity, as measured with the Pelli-Robson Letter CS Chart, in the presence of selected Corning Photochromic Filters (CPF), as compared to performance in the absence of CPF filters, or to that of similarly treated normal observers. These same patients demonstrated reading rates enhanced up to 39% above that measured in the presence of nearpoint optical correction alone. Reading performance of normal observers was unaffected by similar light filtration. These data provide objective evidence for improvement of visual function provided by light-filtering lenses in patients who become photophobic after TBI. Contrast sensitivity testing and assessment of reading rate add objective criteria for the clinical selection of light-filtering lenses in the treatment of TBI-induced photophobia.

Morphologic changes in human carcinoma cells (A-431) stimulated by epidermal growth factor: effect of cholesterol and low-density lipoproteins on the ruffling response.

Stimulation of A-431 carcinoma cells with epidermal growth factor (EGF) causes dramatic morphologic responses including ruffling, rounding, and bulk-phase pinocytosis. In attempts to explore the mechanisms responsible for changes in plasmalemma topography, we have investigated the effects of exogenous sterols thought to alter membrane fluidity. Light and scanning electron microscopy revealed a time- and concentration-dependent inhibition of ruffling (greater than 90%) by cholesterol. This effect could be duplicated by preincubation of the cells with comparable levels of low-density lipoproteins (LDL). EGF-stimulated bulk-phase endocytosis also is inhibited by treatment with cholesterol. No alteration of EGF binding, kinase stimulation, or internalization was detected in cells incubated in cholesterol-enriched medium (175 micrograms/ml in 0.5% ethanol), nor did cholesterol or LDL have any effect on EGF-stimulated rounding. Morphometry of electron micrographs from cholesterol-treated cells revealed a selective depletion of interdigitating lateral surface membrane that normally appears to be recruited to generate apical ruffles. Thus, the sterol inhibition of ruffling may be due to redistribution of plasmalemma rather than to changes in membrane viscosity. Together with previous observations, these data suggest that EGF-stimulated ruffling and bulk-phase pinocytosis are related phenomena, whereas EGF-stimulated cell rounding is an independent process.

Regulation of adrenergic stimulation of hepatic adenylate cyclase by divalent cations.

Liver plasma membrane adenylate cyclase was stimulated paradoxically by an alpha 2-adrenergic mechanism under conditions of low metal ion and low GTP concentrations. In untreated membranes, epinephrine stimulation was GTP-dependent and was mediated by beta-adrenergic receptors since it was completely blocked by propranolol, but unaffected by dihydroergocryptine. Pre-treatment of membranes to remove or reduce divalent cations and guanine nucleotides changed epinephrine stimulation to a form that was mediated by alpha 2-receptors since it was completely blocked by dihydroergocryptine, phenoxybenzamine and yohimbine, but not by propranolol or prazosin. The pre-treatment did not alter enzyme activation by isoproterenol or glucagon, alpha 2-Adrenergic stimulation of adenylate cyclase in depleted membranes required the presence in the assay of 1-2 mM Mg2+ and small amounts of exogenous GTP (less than or equal to 50 nM). Increasing the Mg2+ or GTP concentration in the assay produced a progressive reversal of epinephrine-stimulated activity from an alpha 2-adrenergic form to a predominantly beta-adrenergic form. Readdition of Ca2+ or Mg2+, but not Mn2+, into depleted membranes by incubation in the presence of metal reestablished the pattern of enzyme sensitivity to epinephrine to that seen with untreated membranes i.e., it changed from alpha 2- to beta-receptor mediation. Alterations in membrane and assay content of metal ions and GTP did not result in the activation of the enzyme by vasopressin or angiotensin II. These findings demonstrate the ability of Ca2+, Mg2+ and GTP to control the coupling of beta- and alpha 2-adrenergic receptors with liver adenylate cyclase. It is hypothesized that the cations act by regulating the interaction of the receptors with adrenergic agonists and/or the guanine nucleotide binding protein(s) which is postulated to be involved in control of the enzyme.

Calcium regulation of guanine nucleotide activation of hepatic adenylate cyclase.

Pretreatment of isolated rat liver plasma membranes by washing with NaHCO3 buffer or by exposure to the chelator ethyleneglycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) with or without the ionophore A23187, produced a decrease in the sensitivity of adenylate cyclase (ATP pyrophosphate-lyase (cyclizing) EC 4.6.1.1) to subsequent stimulation by NaF or guanosine 5'-(beta-gamma-imino)triphosphate (GPP(NH)P). Sensitivity to activation by the nucleotide could be restored by addition of the lyophilized and ashed wash or by addition of Ca2+, Mg2+ or Mn2+. The factor extracted from the membranes by these various treatments which was responsible for loss of stimulation was identified as Ca2+. Determination of the metal ion content of isolated membranes by atomic absorption spectrometry indicated that Ca2+ was the only divalent cation present in sufficient concentration to support persistent activation by either NaF or GPP(NH)P. Pretreatment of liver plasma membranes with trifluoperazine, which inhibits the action of Ca2+-dependent regulator protein in other enzyme systems, reduced GPP(NH)P activation of adenylate cyclase and caused marked depletion of membrane Ca2+. The effects of low concentrations (less than 100 microM) of the phenothiazine could be reversed totally by Ca2+ and partly by regulator protein. At higher concentrations of trifluoperazine, slight restoration of enzyme activation was seen with either agent. The hypothesis is presented that Ca2+ interacts with the nucleotide (GTP or GDP) regulatory site(s) of the adenylate cyclase. This interaction may be regulator-protein-dependent and may be important in determining the sensitivity of the enzyme to nucleotide activation in vivo.

The concentration of cyclic AMP and the activity of cyclic AMP dependent protein kinase and an inhibitor in the adipose tissue of rats fed lard or glucose diets.

Measurements of tissue cyclic AMP (cAMP) concentration, the activity of cAMP-dependent protein kinase and the level of the enzyme's thermostable, macromolecular inhibitor were made on preparations of rat epididymal fat pad from animals fed high fat or high carbohydrate diets. The cAMP concentration from rats adapted to a high lard diet for 14-15 days was 153 +/- 17.8 pmoles/mg protein as opposed to 76 +/- 6.0 found with high glucose diet. No significant difference in total cAMP-dependent protein kinase activity was observed among rats fed high glucose, high lard or laboratory chow, although the enzyme's activity ratio (-cAMP)(+cAMP) was significantly elevated with lard feeding (0.49 +/- 0.02) as opposed to glucose feeding (0.43 +/- 0.01). Crude preparations from lard and glucose fed animals were equivalent in inhibitory activity when tested with enzyme from chow fed animals. Agarose column chromatography separated holoenzyme and C subunit forms of the protein kinase when 500 mM NaCl was present in the elution buffer. Absence of the salt allowed subunit reassociation to occur. Direct addition of NaCl greater than or equal to 75 mM significantly inhibited protein kinase activity. The results indicate that the adipose tissue of rats fed a high lard diet has a higher concentration of cAMP and an increased protein kinase activity ratio than tissue from rats fed a fat free, high glucose diet. Total cAMP-dependent protein kinase activity and the level of a thermostable macromolecular inhibitor remained unchanged.