The Relationship between the Shoulder Functional Score and the Change in Labral Morphology after Arthroscopic Bankart Repair

PURPOSE OF THE STUDY

The aim of arthroscopic Bankart repair is restoration of the anterior block mechanism and regaining stability. There are few studies that have tested the adequacy of the angle made with the glenoid and the height from the glenoid level of the repaired labral tissue, but the correlation with the clinical results is not clear. The aim of this study was to defi ne the correlation of the height and slope of the repaired labral tissue in the glenoid anterior with the clinical results. MATERIAL AND METHODS This prospective study included 20 patients who underwent an arthroscopic Bankart repair. To evaluate the labrum anatomy of the affected shoulder, 4 measurement parameters were defi ned as axial height (Ah), axial slope (As), oblique coronal height (Ch), and oblique coronal slope (Cs) on non-contrast T2 MRI. The measurements were taken preoperatively of the affected shoulder and at 1 year postoperatively of both the affected shoulder and the contralateral asymptomatic shoulder. The measured values were compared with each other and with the contralateral shoulder. Correlations of the anatomic values with the Constant-Murley scores recorded at 1, 3, 6, and 12 months postoperatively were examined with the Wilcoxon test. RESULTS The mean preoperative Constant score of the patients was 57.7 (32-77) and postoperative scores at 1, 3, 6, and 12 months were 63.6 (44-79), 77.8 (61-90), 89.6 (77-100), and 95.2 (79-100), respectively (p=0.001). There was a statistically signifi cant difference in the preoperative MRI measurements of the axial and oblique coronal plane labral height and slope values compared to the postoperative values and those of the asymptomatic contralateral shoulder (p< 0.05 for all). There was no statistically signifi cant difference between the labral height and slope values of both planes postoperatively compared to the asymptomatic contralateral shoulder (p= 0.776, p= 0.910, p= 0.132, p= 0.589, respectively). These increases in the radiological data were not found to be statistically signifi cant in the correlation analysis with the increases in the Constant-Murley scores (Ah p=0.935, As p=0.587, Ch p=0.078, Cs p=0.105). CONCLUSIONS This prospective study was conducted using conventional T2 magnetic resonance imaging, which was suffi cient for the measurement of labral height and slope. This study results showed no signifi cant correlation between the radiological and clinical outcomes.

KEY WORDS

Bankart repair, labrum height, labrum slope, functional result.

Testing Hadronic Interactions at Ultrahigh Energies with Air Showers Measured by the Pierre Auger Observatory

Ultrahigh energy cosmic ray air showers probe particle physics at energies beyond the reach of accelerators. Here we introduce a new method to test hadronic interaction models without relying on the absolute energy calibration, and apply it to events with primary energy 6-16 EeV (E_{CM}=110-170  TeV), whose longitudinal development and lateral distribution were simultaneously measured by the Pierre Auger Observatory. The average hadronic shower is 1.33±0.16 (1.61±0.21) times larger than predicted using the leading LHC-tuned models EPOS-LHC (QGSJetII-04), with a corresponding excess of muons.

Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy

We measure the energy emitted by extensive air showers in the form of radio emission in the frequency range from 30 to 80 MHz. Exploiting the accurate energy scale of the Pierre Auger Observatory, we obtain a radiation energy of 15.8±0.7(stat)±6.7(syst)  MeV for cosmic rays with an energy of 1 EeV arriving perpendicularly to a geomagnetic field of 0.24 G, scaling quadratically with the cosmic-ray energy. A comparison with predictions from state-of-the-art first-principles calculations shows agreement with our measurement. The radiation energy provides direct access to the calorimetric energy in the electromagnetic cascade of extensive air showers. Comparison with our result thus allows the direct calibration of any cosmic-ray radio detector against the well-established energy scale of the Pierre Auger Observatory.

Search for patterns by combining cosmic-ray energy and arrival directions at the Pierre Auger Observatory

Energy-dependent patterns in the arrival directions of cosmic rays are searched for using data of the Pierre Auger Observatory. We investigate local regions around the highest-energy cosmic rays with [Formula: see text] eV by analyzing cosmic rays with energies above [Formula: see text] eV arriving within an angular separation of approximately 15[Formula: see text]. We characterize the energy distributions inside these regions by two independent methods, one searching for angular dependence of energy-energy correlations and one searching for collimation of energy along the local system of principal axes of the energy distribution. No significant patterns are found with this analysis. The comparison of these measurements with astrophysical scenarios can therefore be used to obtain constraints on related model parameters such as strength of cosmic-ray deflection and density of point sources.

Measurement of the proton-air cross section at √s=57 TeV with the Pierre Auger Observatory

We report a measurement of the proton-air cross section for particle production at the center-of-mass energy per nucleon of 57 TeV. This is derived from the distribution of the depths of shower maxima observed with the Pierre Auger Observatory: systematic uncertainties are studied in detail. Analyzing the tail of the distribution of the shower maxima, a proton-air cross section of [505±22(stat)(-36)(+28)(syst)] mb is found.

Indication of reactor ν(e) disappearance in the Double Chooz experiment

The Double Chooz experiment presents an indication of reactor electron antineutrino disappearance consistent with neutrino oscillations. An observed-to-predicted ratio of events of 0.944±0.016(stat)±0.040(syst) was obtained in 101 days of running at the Chooz nuclear power plant in France, with two 4.25 GW(th) reactors. The results were obtained from a single 10 m(3) fiducial volume detector located 1050 m from the two reactor cores. The reactor antineutrino flux prediction used the Bugey4 flux measurement after correction for differences in core composition. The deficit can be interpreted as an indication of a nonzero value of the still unmeasured neutrino mixing parameter sin(2)2θ(13). Analyzing both the rate of the prompt positrons and their energy spectrum, we find sin(2)2θ(13)=0.086±0.041(stat)±0.030(syst), or, at 90% C.L., 0.017<sin(2)2θ(13)<0.16.

Measurement of the depth of maximum of extensive air showers above 10{18} eV

We describe the measurement of the depth of maximum, X{max}, of the longitudinal development of air showers induced by cosmic rays. Almost 4000 events above 10;{18} eV observed by the fluorescence detector of the Pierre Auger Observatory in coincidence with at least one surface detector station are selected for the analysis. The average shower maximum was found to evolve with energy at a rate of (106{-21}{+35}) g/cm{2}/decade below 10{18.24+/-0.05} eV, and (24+/-3) g/cm{2}/decade above this energy. The measured shower-to-shower fluctuations decrease from about 55 to 26 g/cm{2}. The interpretation of these results in terms of the cosmic ray mass composition is briefly discussed.

Observation of the suppression of the flux of cosmic rays above 4 x 10 (19) eV

The energy spectrum of cosmic rays above 2.5 x 10;{18} eV, derived from 20,000 events recorded at the Pierre Auger Observatory, is described. The spectral index gamma of the particle flux, J proportional, variantE;{-gamma}, at energies between 4 x 10;{18} eV and 4 x 10;{19} eV is 2.69+/-0.02(stat)+/-0.06(syst), steepening to 4.2+/-0.4(stat)+/-0.06(syst) at higher energies. The hypothesis of a single power law is rejected with a significance greater than 6 standard deviations. The data are consistent with the prediction by Greisen and by Zatsepin and Kuz'min.

Upper limit on the diffuse flux of ultrahigh energy tau neutrinos from the Pierre Auger Observatory

The surface detector array of the Pierre Auger Observatory is sensitive to Earth-skimming tau neutrinos that interact in Earth's crust. Tau leptons from nu(tau) charged-current interactions can emerge and decay in the atmosphere to produce a nearly horizontal shower with a significant electromagnetic component. The data collected between 1 January 2004 and 31 August 2007 are used to place an upper limit on the diffuse flux of nu(tau) at EeV energies. Assuming an E(nu)(-2) differential energy spectrum the limit set at 90% C.L. is E(nu)(2)dN(nu)(tau)/dE(nu)<1.3 x 10(-7) GeV cm(-2) s(-1) sr(-1) in the energy range 2 x 10(17) eV< E(nu)< 2 x 10(19) eV.

Effects of extremely low frequency electromagnetic fields on membrane-associated enzymes

The effects of extremely low frequency electromagnetic fields of 75 Hz were studied on different membrane-associated enzymes. Only the activities of three enzymes out of seven exposed to the field decreased approximately of about 54-61% with field amplitudes above a threshold of 73-151 microT depending on the enzyme. The same field had no effect on the activities of either integral membrane enzymes such as Ca,ATPase, Na/K,ATPase, and succinic dehydrogenase or peripheral membrane enzymes such as photoreceptor PDE. The decrease in enzymatic activity of the field-sensitive enzymes was independent of the time of permanence in the field and was completely reversible. When these enzymes were solubilized with Triton, no effect of the field was obtained on the enzymatic activity, suggesting the crucial role of the membrane in determining the conditions for enzyme inactivation. The role of the particular linkage of the field-sensitive enzymes to the membranes is also discussed.

Measurement of the D(s)+ lifetime

A high statistics measurement of the D(s)+ lifetime from the Fermilab fixed-target FOCUS photoproduction experiment is presented. We describe the analysis of the two decay modes, D(s)+ --> phi(1020)pi+ and D(s)+ -->K*(892)0K+, used for the measurement. The measured lifetime is 507.4 +/- 5.5(stat) +/- 5.1(syst) fs using 8961 +/- 105 D(s)+ --> phi(1020)pi+ and 4680 +/- 90 D(s)+ --> K*(892)0K+ decays. This is a significant improvement over the present world average.

Effects of extremely low frequency electromagnetic fields on the adenylate kinase activity of rod outer segment of bovine retina

Extremely low frequency electromagnetic fields (ELF-EMFs) of 75 Hz with amplitudes above a threshold of about 125 microT have a dramatic effect on the adenylate kinase (AK) activity of the rod outer segment (ROS) membranes. In fact, the ATP production by ROS membranes or by purified disk membranes placed in the field decreased by approximately 54%. The decrease in enzymatic activity was independent of the time of exposure to the field and was completely reversible. When disk membranes were solubilized with Triton or a soluble isoform of AK was used, negligible effects of the field were obtained on the enzymatic activity, suggesting that the membrane has an important role in determining the conditions for the enzyme inactivation.

Electromagnetic field of extremely low frequency decreased adenylate kinase activity in retinal rod outer segment membranes

Adenylate kinase activity in rod outer segment membranes of bovine retina decreased of about 55% when exposed to an extremely low frequency electromagnetic field of 75 Hz and 250 microT. The effect was independent of the time of permanence in the field. Negligible effects of the field were found on the enzymatic activity of a soluble isoform of adenylate kinase or of rod outer segment membranes solubilized with Triton, suggesting the importance of the membrane in determining the conditions of the enzyme inactivation.

A high statistics measurement of the Lambda(+)(c) lifetime

A high statistics measurement of the Lambda(+)(c) lifetime from the Fermilab fixed-target FOCUS photoproduction experiment is presented. We describe the analysis technique with particular attention to the determination of the systematic uncertainty. The measured value of 204.6 +/- 3.4 (stat) +/- 2.5 (syst) fs from 8034 +/- 122 Lambda(+)(c)-->pK(-)pi(+) decays represents a significant improvement over the present world average.

ATP synthesis in the disk membranes of rod outer segments of bovine retina

ATP is synthesized on the disk membrane isolated from rod outer segments of the bovine retina. Together with a slow component which accounted for a constant rate of about 22 nmol ATP/min/mg of protein and which was due to the adenylate kinase activity, a fast component with a maximal activity of about 58 nmol ATP/min/mg of protein was measured at physiological calcium concentrations. This fast activity disappeared in the presence of the Ca(2+) ionophore A23187, was inhibited by vanadate or thapsigargin but not by oligomycin, suggesting that this ATP synthesis is due to the reversal functioning of the Ca(2+)-ATPase previously found on the disk membranes.

Search for CP violation in the decays D+--> K(S)pi+ and D+-->K(S)K+

A high-statistics sample of photoproduced charm from the FOCUS experiment has been used to search for direct CP violation in the decay rates for D+-->K(S)pi+ and D+-->K(S)K+. We have measured the following asymmetry parameters relative to D+-->K-pi+pi+: A(CP)(K(S)pi+) = (-1.6+/-1.5+/-0.9)%, A(CP)(K(S)K+) = (+6.9+/-6.0+/-1.5)%, and A(CP)(K(S)K+) = (+7.1+/-6.1+/-1.2)% relative to D+-->K(S)pi+. We have also measured the relative branching ratios and found Gamma(D+-->K(0)pi+)/Gamma(D+-->K-pi+pi+) = (30.60+/-0.46+/-0.32)%, Gamma(D+-->K(0)K+)/Gamma(D+-->K-pi+pi+) = (6.04+/-0.35+/-0.30)%, and Gamma(D+-->K(0)K+)/Gamma(D+-->K(0)pi+) = (19.96+/-1.19+/-0.96)%.

Recent advances in our understanding of rhodopsin and phototransduction

The present models of phototransduction for vertebrates and invertebrates have been reviewed and the relative literature updated. The emerging picture for vertebrate phototransduction is a result of a better knowledge of its general outlines, although some important details such as the role of calcium ions are still lacking. The molecular events involved in the rising phase of the electrical response have basically been understood, whilst those involved in response inactivation and recovery remain to be elucidated. In an overall strategy, the phototransduction in invertebrates shares a great deal of similarity with that in vertebrates but differs in the underlying molecular events. However, a complete picture of phototransduction in invertebrate photoreceptors has not yet emerged. The available data on the structure of the visual pigment rhodopsin reveal further details on the present model of the retinal-binding pocket of the protein and consequently of the "red shift" of the absorbance of retinal. The problem of the energy supplied during photoreception, in particular, the availability of ATP in the rod outer segment and the presence in the disk membranes of a Ca-ATPase are discussed. Finally, recent progress in understanding the molecular mechanisms of inherited retinal diseases and relative gene identification are summarized.

Measurement of the branching ratios of D(+) and D(+)(s) hadronic decays to four-body final states containing a K(S)

We have studied hadronic four-body decays of D(+) and D(+)(s) mesons with a K(S) in the final state using data recorded during the 1996-1997 fixed-target run of the Fermilab high energy photoproduction experiment FOCUS. We report a new branching ratio measurement of gamma(D(+)-->K(S)K-pi(+)pi(+))/gamma(D(+)-->K(S)pi(+)pi(+)pi(-)) = 0.0768+/-0.0041+/-0.0032. We make the first observation of three new decay modes with branching ratios gamma(D(+)-->K(S)K+pi(+)pi(-))/gamma(D(+)-->K(S)pi(+)pi(+)pi(-)) = 0.0562+/-0.0039+/-0.0040, gamma(D(+)-->K(S)K+K-pi(+))/gamma(D(+)-->K(S)pi(+)pi(+)pi(-)) = 0.0077+/-0.0015+/-0.0009, and gamma(D(+)(s)-->K(S)K+pi(+)pi(-))/gamma(D(+)(s)-->K(S)K-pi(+)pi(+)) = 0.586+/-0.052+/-0.043, where in each case the first error is statistical and the second error is systematic.

Adenylate kinase activity in rod outer segments of bovine retina

The rod outer segments of bovine retina contain two different adenylate kinases: a soluble activity, which is not sensitive to calcium ion, and an activity bound to disk membranes, which is dependent on the calcium levels. In fact, the maximal activity associated to the disks is reached at Ca(2+) concentrations between 10(-6) and 10(-7) M, which is the range of calcium level actually present in the rod cell. The Michaelis-Menten kinetics of the enzyme activity on disk membranes was determined and the actual concentrations of ATP, AMP and ADP were measured in the photoreceptor outer segment. Therefore, the physiological relevance of the adenylate kinase activity was discussed considering the above results. The formation of ATP catalyzed by the enzyme seems appropriate to supply at least some of the reactions necessary for phototransduction, indicating that ATP could be regenerated from ADP directly on the disk membranes where the photoreception events take place.

Study of the decay D0 --> K+pi-

Using a large sample of photoproduced charm mesons from the FOCUS experiment at Fermilab (FNAL-E831), we observe the decay D0-->K+pi- with a signal yield of 149+/-31 events compared to a similarly cut sample consisting of 36 760+/-195 D0-->K-pi+ events. We use the observed ratio of D0-->K+pi- to D0-->K-pi+ (0.404+/-0.085+/-0.025)% to obtain a relationship between the D0 mixing and doubly Cabibbo suppressed decay parameters.

ATP synthesis in rod outer segments of bovine retina by the reversal of the disk Ca(2+) pump

Purified disk membranes from rod outer segments of the bovine retina were able to synthesize ATP with a maximal activity (about 52 nmoles ATP/min/mg of protein) at physiological calcium concentrations. This activity was inhibited by vanadate or thapsigargin but not by oligomycin, suggesting the reversal functioning of the disk Ca(2+)-ATPase, which would act as a ATP synthesizer at the expense of the calcium gradient between the disks and the cytoplasm of the rod outer segment. The results are discussed in terms of the need of an immediate source of ATP on the disk membranes where the energy is required to supply the rapid reactions of the photoreception processes.

Rhodopsin and phototransduction

Recent studies on rhodopsin structure and function are reviewed and the properties of vertebrate as well as invertebrate rhodopsin described. Open issues such as the 'red shift' of the absorbance spectra are emphasized in the light of the present model of the retinal-binding pocket. The processes that restore the rhodopsin content in photoreceptors are also presented with a comparison between vertebrate and invertebrate visual systems. The central role of rhodopsin in the phototransduction cascade becomes evident by examining the main reports on light-activated conformational changes of rhodopsin and its interaction with transducin. Shut-off mechanisms are considered by reporting the studies on the sites of rhodopsin phosphorylation and arrestin binding. Furthermore, recent findings on the energetics of phototransduction point out that the ATP needed for photoreception in vertebrates is synthesized in the outer segments where phototransduction events take place.

A multiwire proportional counter for very high counting rates

Preliminary measurements in a proportional counter with two independently counting wires showed that counting rates up to 10(6) counts s(-1) wire(-1) can be reached without critical loss in the 'true versus measured' linearity relation. Results obtained with a detector containing 30 active wires (2 mm pitch) are presented. With each wire is associated a fast pre-amplifier and a discriminator channel. Global counting rates in excess of 10(7) events s(-1) are reported. Dead-time losses are corrected by use of simple mathematical-modelling functions. Data-acquisition systems are described for one-dimensional (real-time) and two-dimensional (off-line) position-sensitive detection systems.

Langmuir-Blodgett films of photosensitive proteins

The striking properties of monolayers and multilayers of photosensitive proteins obtained by using the Langmuir-Blodgett technique are described. The close packing of the protein molecules, which preserve most of the properties found in solution, seems to be the main cause for their thermal stability, which in some cases reached a temperature of 200 degrees C without the loss of the protein secondary structure. The review is focused on three of the most intensively studied photosensitive proteins, namely photosynthetic reaction centres, bacteriorhodopsin and bovine rhodopsin, and on their possible applications as molecular optical devices.

Characterization of Langmuir-Blodgett films of rhodopsin: thermal stability studies

Two-dimensional close packing of purified bovine rhodopsin, made by the Langmuir-Blodgett technique, was characterized by small angle x-ray scattering and nanogravimetric measurements. The area occupied by a molecule of rhodopsin in the film was approximately 1100 Angstrum2 and the periodicity of the layers resulted in 59 Angstrum. The circular dichroism measurements showed that bleached rhodopsin in Langmuir-Blodgett film had high thermal stability, in fact, reaching a temperature of 150 degrees C without a loss of the secondary structure. Moreover, when the film was made up in the dark, rhodopsin maintained its stability up to at least 200 degrees C and its characteristic absorbance peak at 500 nm up to about 90 degrees C.

Endoplasmic reticulum Ca(2+)-ATPase in microsomal vesicles isolated from bovine retinae

Active Ca2+ transport was measured in microsomal vesicles prepared from bovine retinae and was compared with that in disk membranes of the photoreceptor cells of the same retina. The 45Ca uptake was dependent on the presence of Mg(2+)-ATP and was inhibited by vanadate or when GTP substituted for ATP. The dependence of calcium uptake on the external free Ca2+ concentration gave a KM = 13 microM or a KM = 0.1 microM for disks and microsomal vesicles, respectively. A phosphorylated intermediate (E-P) of Ca(2+)-ATPase of about 100 kDa was isolated in microsomal vesicles. The E-P formation was strongly inhibited by thapsigargin and partially by 2,5-di-(-butyl)benzohydroquinone. Digestion of disks or microsomes with calpain had no effect on the phosphorylated intermediate, while digestion with trypsin produced two fragments of approximately 55 kDa and 35 kDa. These results suggest that bovine retinal microsomes contain a calcium pump belonging to the SERCA family.

Characterization of Ca(2+)-ATPase in rod outer segment disk membranes

The Ca(2+)-pump isolated in rod outer segment disk membranes as aspartylphosphate intermediate E-P has been characterized: the 100 kDa phosphoprotein was completely inhibited by thapsigargin, was not sensitive to digestion by calpain, and displayed a tryptic digestion pattern with the formation of two autophosphorylatable fragments of about 55 and 35 kDa. These results are typical of the calcium pumps of sarcoplasmic or endoplasmic reticulum calcium and differ from those of plasma membrane, such as the Ca(2+)-ATPase of the red blood cells, here shown as controls. The physiological role of calcium pump in disk membranes of vertebrate photoreceptors is discussed in terms of intracellular calcium buffering.

Calcium pump in the disk membranes isolated from bovine retinal rod outer segments

The existence of a Ca2+ pump in rod outer segment disks of bovine retina is strongly suggested by the isolation on sodium dodecyl sulfate polyacrylamide gel electrophoresis of a hydroxylamine-sensitive phosphorylated intermediate (E-P) of molecular mass of about 100 kDa as well as by measurements of active calcium transport and adenosine 5'-triphosphate (ATP) hydrolysis. Active Ca2+ uptake by disks was dependent on the presence of Mg(2+)-ATP, was inhibited by vanadate or lanthanum and appeared poorly sensitive to calmodulin. ATP hydrolysis by disk membranes was a function of free Ca2+ concentration in the absence of exogenous Mg2+. The presence of a Ca2+ pump on disk membranes is discussed in terms of its possible role in Ca2+ ion buffering during photoreceptor cell functioning.

A study on retinal photoisomerization catalyzed by a protein from the honeybee visual system

The photoisomerization of all-trans retinal catalyzed by an isomerase purified from the honeybee retina is stereospecifically directed toward the formation of 11-cis retinal, the isomer required for rhodopsin regeneration. A model of the enzymatic reactions was developed, which fits the experimental data. In a particular experiment where irradiation was performed with a LASER light, the rate constants of the photoisomerization of all-trans retinal were dependent on the light intensity and were therefore greatly enhanced.

Resolution and characterization of two forms of phosphoinositide-specific phospholipase C from bovine rod outer segments

Two forms (I and II) of phospholipase C, specific for phosphatidyl inositol 4,5-bisphosphate, were resolved from bovine retinal rod outer segment (ROS) cytosol by DEAE-Sepharose column chromatography. The two isozymes showed reproducible differences in their catalytic properties in spite of similar substrate specificity and hydrolyzed specifically inositol 4,5-bisphosphate in a Ca(2+)-dependent fashion. In the presence of deoxycholate (DOC), pH optima were at 6.5 and 7.0 for phospholipase C I and II, respectively. Maximal phosphatidylinositol 4,5-bisphosphate hydrolysis rates were obtained at 10(-4) and 10(-5)M Ca2+ for phospholipase C I and II, respectively. Treatment with cAMP-dependent protein kinase did not alter either isozyme activity. Further purification steps were prevented by the extreme lability of the isozymes.

Retinal photoisomerase: role in invertebrate visual cells

In invertebrate visual cells, the rhodopsin content is maintained at a high level by the fast process of photoregeneration during daylight. Rhodopsin is converted by photoabsorption to metarhodopsin, which is reconverted to rhodopsin by light. In addition, rhodopsin is regenerated by a slow process of renewal which takes days to complete and involves the biosynthesis of opsin. It is well known that rhodopsin can be formed from opsin only when 11-cis-retinal is present; this requires the existence of an isomerizing enzyme which is capable of transforming all-trans-retinal, released from the degradation of metarhodopsin, into the 11-cis-retinal isomer. In some invertebrate visual systems, experiments on rhodopsin regeneration have been interpreted by assuming that the isomerization reaction is a light-dependent process involving a retinal-protein complex. Two retinal photoisomerases which have been well characterized, i.e. bee photoisomerase and cephalopod retinochrome, are reviewed here. Their properties are compared in order to determine their physiological role, which is likely to be in the renewal of visual pigment rhodopsin. To conclude, a visual pigment cycle is proposed in which rhodopsin regeneration follows two light-dependent pathways. This greatly simplifies the rhodopsin regeneration scheme for invertebrate visual systems.

Phosphatidyl inositol 4,5-bisphosphate-specific phospholipase C in bovine rod outer segment membranes

Polyphosphoinositide-specific phosphodiesterase (phospholipase C) activity against phosphatidylinositol 4,5-bisphosphate has been examined in disrupted bovine retinal rod outer segments. The enzyme was strictly modulated by free calcium ion concentration and maximally activated at 10(-5) M Ca2+ (91 +/- 4 nmoles phosphatidylinositol 4,5-bisphosphate hydrolyzed/min/mg of protein). Guanine nucleotides did not affect in vitro phospholipase C activity either in the presence or absence of light, carbachol or epinephrine. The pH optimum at 10(-5) M Ca2+ in the presence of sodium deoxycholate was 6.5. The enzyme of bovine rod outer segments was concluded to be indirectly regulated by the phototransduction events.

Rhodopsin reconstitution in bleached rod outer segment membranes in the presence of a retinal-binding protein from the honeybee

The physiological role of a retinal-binding protein from honeybee is investigated. This protein, upon previous loading with all-trans retinal and subsequent irradiation with monochromatic light of wavelength 490 nm, is able to promote the reconstitution of rhodopsin when added to a suspension of opsin membranes from bleached bovine rod outer segments. In this respect this retinal-binding protein could have a role very similar to that postulated for the well-known cephalopod retinochrome, that serves to catalyze the formation in the presence of light of 11-cis retinal in photo-receptor cells and to provide it for the reconstitution of rhodopsin during the visual cycle.

Visual transduction in vertebrate photoreceptors. Light activation of guanylate cyclase

Light activation of guanylate cyclase at different calcium concentrations was studied in the rod outer segments of the toad retina. The enzyme becomes sensitive to calcium ions after a flash of light, showing an enhancement of its activity when Ca2+ concentration is lowered from 10(-4) M to 10(-8) M. A possible pathway of guanylate cyclase activation by light was also investigated by means of the antibody 4A to transducin. When added in excess to transducin, the antibody inhibits light activation of phosphodiesterase as well as of cyclase, suggesting a possible coupling of the two enzymes.

Can metarhodopsin I activate rod outer segment phosphodiesterase?

The rod photoreceptors of vertebrate retinas contain a cGMP phosphodiesterase (PDE) that is activated by light. The light is absorbed by rhodopsin that activates an intermediate GTP-binding protein; this species then activates the PDE. Photo-excited rhodopsin passes through a series of transient states, and the purpose of this study is to identify the earliest state that interacts with the GTP-binding protein and thus activate the PDE. The majority of evidence points to this state being metarhodopsin II (MII), but PDE activation is seen at low temperatures where the rhodopsin reaction sequence is not expected to pass beyond the metarhodopsin I (MI) stage. Light thresholds for PDE activation have been determined under conditions where little MII is generated, and these are compared with the concentration of MII. The conclusion is that for a criterion threshold of PDE activity, the MII concentration is constant, irrespective of the amount of MI present, which suggests that MI cannot activate the PDE system.

Structure of a protein catalyzing the formation of 11 cis-retinal in the visual cycle of invertebrate eyes

A pigment made up of a protein able to bind retinal as well as retinol is described. The molecule consists of a dimer with a molecular weight of 50,000 which binds one molecule of retinal. The binding site for retinal is a Schiff base buried in the interior of the protein. Retinol is probably bound to the protein in the same site as for retinal, although not covalently, as suggested by the absorbance spectra. The protein, extracted from honeybee retina, is involved in visual pigment metabolism, and its structure may elucidate the mechanism of the stereospecific photoisomerization of all trans-retinal to 11-cis-retinal.

Effect of light and calcium on cyclic GMP synthesis in rod outer segments of toad retina

The rod outer segments of toad retina contain a guanylate cyclase activity of about 3 +/- 1 nmol of cGMP formed/min per mg protein. In darkness this value is largely independent of the Ca2+ concentration, although it is enhanced by light upon lowering the Ca2+ concentration from 10(-5) to 10(-8) M. The activating effect of light on cyclase at low Ca2+ concentrations is enlarged upon increasing the light intensity. With a flash of light bleaching 7 X 10(-2) percent of rhodopsin, cyclase activity increased by a factor of 30 when Ca2+ levels dropped from 10(-5) to 10(-8) M. In view of recent observations that shortly after a flash of light the calcium activity inside the photoreceptor cell decreases, it seems likely that Ca2+ plays a regulatory role on cGMP metabolism in visual excitation.

Guanylate cyclase in rod outer segments of the toad retina. Effect of light and Ca2+

Guanylate cyclase activity was measured in disrupted rod outer segments of the toad retina. The experiments showed that cGMP is synthesized from GTP at a rate of 3 +/- 1 nmol/min per mg protein. In darkness this value is largely independent of the Ca2+ concentration, while it is enhanced by flashes of light of increasing intensity upon lowering Ca from 10-5 to 10-8 M. In view of recent observations that shortly after a flash of light calcium activity inside the photoreceptor cell decreases, it seems likely that calcium plays a regulatory role in cGMP metabolism in visual excitation.

Characteristics of retinal-binding proteins from the honeybee retina

Spectrophotometric studies were performed on two water soluble retinal-binding proteins isolated from honeybee retina. Both pigments, B and C, absorb maximally at about 440 nm. Pigment B is bleached by light to a photoproduct with lambda max at about 370 nm. This pigment reacts with hydroxylamine in the dark to form a product with an absorbance maximum at 360 nm, whereas with cyanoborohydride it reacts only in the light forming a product with lambda max at about 330 nm. Irradiation of pigment C also leads to the formation of a photoproduct with lambda max at about 370 nm but, in contrast to that of pigment B, it reconverts to its 440 nm-form during the following dark period. The results obtained by changing the pH of the extracts support the hypothesis that all-trans retinal binds to each protein via a Schiff base linkage (pK of 8.4). The data are discussed with relation to the physiological role pigment B could play in the visual cycle of honeybees.

Incorporation into lipid bilayer membranes of a photo--sensitive pigment from the honeybee compound eye

An increase of electrical conductance up to a factor 10(2)--5-10(2) was obtained by adding, in the dark, the honeybee photopigment to a positively charged lipid bilayer. The increase in conductance was made slower by illuminating the system during the incorporation of the protein into the membrane and it was negligible when the photopigment was bleached before the incorporation. The interaction of the photopigment with the membrane is tentatively interpreted in terms of formation of channels.