Biomedical subjects

R E Anderson

Publications and source records attributed to R E Anderson.

At least 145 records · Page 8Linked to original sources

PubMed1993

Synthesis of docosahexaenoic acid by retina and retinal pigment epithelium.

Rod outer segments of vertebrate retinas are highly enriched in docosahexaenoic acid (22:n-3), a fatty acid that is essential for optimal retinal function. The high levels of retinal 22:6n-3 are maintained through conservation (recycling) within the eye and incorporation from the circulation. The liver is thought to be a major source of 22:6n-3 through synthesis from appropriate n-3 precursors and delivery to target tissues via plasma lipoproteins. The contribution of other tissues to the total body pool of 22:6n-3 is not known. We investigated the synthesis of 22:6n-3 from [1-14C]18:3n-3 or [3-14C]22:5n-3 in frog retina and retinal pigment epithelium (RPE). RPE cells rapidly converted each precursor to 22:6n-3, which contained about 23 and 35%, respectively, of the label after 8 h. Significant labeling of 24:6n-3 and 24:5n-3 occurred when [3-14C]22:5n-3 was the substrate. In contrast, the major end products of retinas incubated with [1-14C]18:3n-3 and [3-14C]22:5n-3 were 18:4n-3 and 20:5n-3, respectively, neither of which is found in retinal lipids. Less than 5% of the radioactivity from either precursor was in 22:6n-3 after an 8-h incubation. Our results demonstrate an active in vitro synthesis of 22:6n-3 in frog RPE, but not in the retina. The labeling of 24:5n-3 and 24:6n-3 is consistent with the proposal of Voss et al. [Voss, A., Reinhart, M., Sankarappa, S., & Sprecher, H. (1991) J. Biol. Chem. 266, 19995-20000] that they are intermediates in the conversion of 22:5n-3 to 22:6n-3. Since frog RPE contains measurable amounts of 18:3n-3, 20:5n-3, and 22:5n-3, which are readily converted to 22:6n-3 in these cells, we suggest that the RPE is a source of 22:6n-3 for the retina.

Animals↗

PubMed1993

Transport of 22:6n-3 in the plasma and uptake into retinal pigment epithelium and retina.

Vertebrate retina is highly enriched in 22-carbon polyunsaturated fatty acids (PUFAs), especially docosahexaenoic acid (DHA, 22:6n-3), which is supplied by the plasma. To study the transport and uptake of 22:6n-3 into the retina, young Long Evans rats were fasted overnight and given an oral dose of palm oil containing [4,5-3H] 22:6n-3 and [9,10-3H] 18:1n-9 (oleic acid). At 1, 6, 12, 24, and 48 hr postgavage, blood, liver, retinal pigment epithelium (RPE) and retina were collected, and plasma lipoprotein fractions were obtained by density-gradient ultracentrifugation. The distribution of radioactivity among the different lipoproteins (dpm%) showed that both fatty acids were mainly associated with VLDL 1 hr after gavage. For 22:6n-3, the majority of radioactivity was associated with LDL at 6 hr postgavage. By 12 hr post administration, the majority of radioactivity was in HDL2 which retained around 40% until the 48-hr time point. For 18:1n-9, a different profile was observed. By 6 hr postgavage, approximately 30% of the radioactivity was found in HDL2, but the percentage of radioactivity decreased to approximately 20% thereafter. The half-life of 22:6n-3 was significantly longer than for 18:1n-9 (P < 0.0005) in plasma, liver, and the lipoprotein fractions. The specific activities of 22:6n-3 and 18:1n-9 in the plasma continuously declined from 1 hr to 48 hr postgavage, while liver showed a peak of specific activity at 6 hr, then gradually declined.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Metabolism in frog retinal pigment epithelium of docosahexaenoic and arachidonic acids derived from rod outer segment membranes.

Frog photoreceptor cells shed about 10% of their rod outer segments (ROS) every 4th day. Packets of these membranes are phagocytized and digested by retinal pigment epithelial (RPE) cells. Large amounts of lipids must be processed daily, especially docosahexaenoic acid (22:6n-3, DHA), the major fatty acid of these membranes. To study the metabolism of ROS lipids in RPE cells, RPE-eyecups were incubated with [3H]DHA-, [3H]arachidonic acid (AA)-, or [2-3H]glycerol-labeled ROS membranes for 2 hr, followed by a chase for up to 8 hr. Lipid extracts of RPE cells and incubation media were resolved into classes and quantitated for radioactivity. In RPE cells, the relative proportion of DHA and AA label in triglycerides (TG) increased dramatically with incubation time, although the substrate ROS membranes did not contain labeled TG. Other RPE lipids showed prominent reductions or relative little change. The percentage of radioactivity in free fatty acids (FFA) was low (< 3%) in RPE cells. In the chase media, the majority (60-80%) of DHA and AA label was found in FFA, with little radioactivity in TG or phospholipids. When RPE cells were incubated with [3H]glycerol-labeled ROS membranes which contained 22% of the label in TG, the most rapid reduction in relative radioactivity appeared in TG. We conclude that DHA and AA are released from phagocytized ROS membranes and are rapidly incorporated into RPE cellular lipids, primarily TG. This lipid class is very active metabolically, since TG derived from ROS are rapidly hydrolysed. Free DHA and AA of ROS origin are released from RPE cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Effect of arterial blood pressure and serum glucose on brain intracellular pH, cerebral and cortical blood flow during status epilepticus in the white New Zealand rabbit.

Generalized seizures can induce both hypertension and hyperglycemia which may aggravate preexisting cerebral or medical conditions in patients. In vivo fluorescent imaging of regional cortical blood flow and brain intracellular pH (pHi) was performed in fasted New Zealand rabbits (n = 35) in which either mean arterial blood pressure (MABP) or serum glucose was the covaried factor during pentylenetetrazole induced status epilepticus under 1.5% inspired halothane. Baseline brain pHi and regional cortical blood flow were 7.02 +/- 0.02 and 51.1 +/- 1.7 ml/100 g/min, respectively. Following seizure induction, MABP increased to 105 mm Hg and brain pHi fell to 6.79 +/- 0.03 within 15 min and remained at this level for 1 h (P < 0.001). With normalization of MABP during ongoing seizures, there was no worsening in brain pHi despite a significant decrease in regional cortical blood flow. Hyperglycemia decreased pHi to 6.71 +/- 0.02 compared to 6.84 +/- 0.04 in normoglycemic animals (P < 0.001). Using pHi as a cerebral metabolic index, these data suggest that normalization of MABP does not increase metabolic injury while hyperglycemia does significantly worsen brain acidosis. Therefore, administration of glucose to patients with status epilepticus should be avoided unless there is documented hypoglycemia.

Animals↗

PubMed1993

An autopsy-based quality assessment program for improvement of diagnostic accuracy.

A program for quality assessment of medical diagnostics is proposed, based on detailed, ongoing comparison of clinical diagnoses with autopsy diagnoses. The model requires that the autopsy service itself be subjected to quality control to assure the reliability of the autopsy findings, including the quality of diagnoses made postmortem, and the quality of autopsy reports. Discrepancies between premortem and postmortem diagnoses are classified as to cause and magnitude; for each disease, the total diagnostic experience is collected, and sensitivity and specificity of clinical diagnostics are computed. These are compared with control ranges of sensitivity and specificity, prospectively arrived at through analysis of thousands of cases. Statistically acceptable sampling for autopsy, and review of findings by an independent body are also discussed. The findings generated by this program would be of great value in programs for quality improvement of medical care. The model has the following advantages: (1) it recognises that there is an unavoidable baseline of diagnostic errors; (2) the control levels, based on current medical practice, are prospectively established; (3) it avoids placing blame in a single case; and (4) it provides a fairly high power scrutiny that can focus on diagnostics for single diseases rather than the entire spectrum of medical practice.

Autopsy↗

PubMed1993

Effect of superhypercapnia on cortical pHi and cortical blood flow.

In vivo panoramic imaging of regional cortical blood flow and intracellular brain pH with umbelliferone fluorescence was performed in fasted New Zealand White rabbits (n = 30) subjected to constant or stepwise increases in arterial PCO2 (PaCO2) up to 160 mmHg under 1.0% halothane anesthesia. At a PaCO2 of 40 mmHg, baseline brain pHi measured 7.03 +/- 0.04, while regional cortical blood flow was 47.0 +/- 4.3 ml.100 g-1.min-1. With an immediate but constant exposure to a PaCO2 of 60, 80, or 120 mmHg, at 15 min pHi fell to 6.94 +/- 0.03, 6.89 +/- 0.03, and 6.90 +/- 0.03 and recovered over 20, 80, and 120 min, respectively. At 160 mmHg PaCO2, pHi fell to 6.68 +/- 0.04 and remained acidotic. With stepwise increases in PaCO2 up to 80 mmHg, brain pHi decreased from 7.01 +/- 0.02 to 6.99 +/- 0.02, not significantly different despite a severe systemic acidosis of 7.022 +/- 0.034. At a PaCO2 of 120 and 160 mmHg, pHi dropped to 6.97 +/- 0.02 and 6.93 +/- 0.02, respectively. The difference in brain pHi between an immediate and stepwise exposure to a PaCO2 of 160 mmHg was significant (P < 0.005). These results demonstrate that brain pHi is tightly regulated across the cortical surface and resistant to profound changes in extracellular pH. The difference in pHi between the constant and incremental increases in PaCO2 suggests that there is upregulation of pH homeostatic mechanisms.

Animals↗

PubMed1993

Acidic foci within the ischemic penumbra of the New Zealand white rabbit.

BACKGROUND AND PURPOSE: In vivo panoramic imaging of reduced nicotinamide adenine dinucleotide (NADH), intracellular brain pH (pHi), and cortical blood flow was used to characterize the ischemic penumbra during focal ischemia. During global ischemia, hypoxia, and status epilepticus, the development of cortical acidic foci has been observed. The hypothesis tested was that during focal ischemia, acidic foci develop, which may lead to recruitment of the ischemic penumbra into infarction. METHODS: Five fasted New Zealand White rabbits underwent middle cerebral artery (MCA) occlusion under 1.5% halothane anesthesia through a retro-orbital approach, and five animals served as controls. Brain pHi and cerebral blood flow were measured with in vivo umbelliferone fluorescence. RESULTS: Baseline brain pHi was 6.98 +/- 0.05, whereas cortical blood flow and NADH fluorescence measured 52.2 +/- 8.7 mL/100 g per minute and 35.5 +/- 3.7 gray-scale units, respectively. Fifteen minutes after MCA occlusion, overall brain pHi and cortical blood flow of the ischemic penumbra measured 6.61 +/- 0.06 and 31.9 +/- 9.2 mL/100 g per minute. Over 3 hours there was normalization of pHi in the majority of the penumbra due to increases in cortical blood flow. Within the ischemic penumbra acidic foci developed with an initial pHi of 6.35 +/- 0.09 and cortical blood flow of 18.0 +/- 5.7 mL/100 g per minute. These foci remained acidic with increased NADH fluorescence despite being surrounded by cortex that was recovering from ischemia. On light microscopy, these acidic foci had a mixed pattern of neuronal injury. CONCLUSIONS: Within the ischemic penumbra, acidic foci develop that do not follow a vascular distribution and have microscopic evidence of ischemic neuronal injury. This suggests that there is a cortical selective vulnerability regarding pHi regulation and these acidic foci may lead to recruitment of the ischemic penumbra into infarction.

Acidosis↗

PubMed1993

Brain pHi, cerebral blood flow, and NADH fluorescence during severe incomplete global ischemia in rabbits.

BACKGROUND AND PURPOSE: The aim of this experiment was to study the serial changes in brain intracellular pH, cerebral blood flow, and the oxidation/reduction level of intramitochondrial nicotinamide adenine dinucleotide fluorescence across the cortical surface during severe incomplete global ischemia. METHODS: Reduced nicotinamide adenine dinucleotide fluorescence and brain intracellular pH using the pH-sensitive indicator umbelliferone were measured with in vivo panoramic fluorescence imaging of the cortical surface. Cerebral blood flow was measured with the clearance of both umbelliferone and xenon-133. Fifteen minutes of severe incomplete global ischemia was produced by temporary occlusion of the innominate, left carotid, and subclavian arteries in five fasted New Zealand White rabbits. RESULTS: Baseline brain intracellular pH was homogeneous over the exposed cortex, measuring 7.00 +/- 0.02, while cerebral blood flow was 48.0 +/- 2.6 ml/100 g/min. During 15 minutes of ischemia, cerebral blood flow measured 6.3 +/- 1.8 ml/100 g/min and brain pH declined to 6.61 +/- 0.02 (p < 0.005); in addition, there were acidotic foci with pH measuring 6.40 +/- 0.10. During reperfusion, there was an initial normalization of brain intracellular pH without an alkaline shift followed by a recurrent cortical acidosis of pH 6.88 +/- 0.06. There was a heterogeneous pattern of fluorescence that increased significantly following 60 minutes of reperfusion, coinciding with a postischemic hypoperfusion. The hypoperfusion was a uniform reduction in cerebral blood flow over the brain's surface, with reductions of 42.5% and 44.2% at 30 and 45 minutes, respectively. CONCLUSIONS: During incomplete global ischemia there is a heterogeneous pattern of brain intracellular pH and reduced nicotinamide adenine dinucleotide changes that do not correlate with changes in cortical blood flow. The acidotic foci that were approximately 0.2 pH units more acidotic than the surrounding cortex may be the result of continued glucose delivery under anaerobic conditions. The degree of reduced nicotinamide adenine dinucleotide fluorescence suggests that the cortex is most vulnerable to metabolic failure after 60 minutes of reperfusion following severe incomplete global ischemia. The heterogeneous pattern of brain intracellular pH and reduced nicotinamide adenine dinucleotide changes suggest that there may be a selective vulnerability of cortical tissue to an ischemic challenge.

Animals↗

PubMed1993

Neuroprotection by corticotropin releasing factor during hypoxia in rat brain.

BACKGROUND AND PURPOSE: Corticotropin releasing factor is an endogenous neuropeptide released by the hypothalamus that activates the pituitary-adrenocortical system in response to stressful stimuli. It has been demonstrated that corticotropin releasing factor increases the excitability of hippocampal neurons in both in vitro and in vivo studies, which may contribute to neurological injury during hypoxia. The purpose of this study was to determine the effects of corticotropin releasing factor and its synthetic competitive antagonist, alpha-CRF, on neuronal synaptic recovery after a hypoxic insult using the hippocampal slice. METHODS: Wistar rat hippocampal brain slices (n = 120) were treated with various concentrations (10(-6) to 10(-11)) of corticotropin releasing factor or its synthetic antagonist during a 10-minute hypoxic episode. Extracellular recording of population spikes was used during and after the hypoxic insult to assess neuronal recovery. RESULTS: Corticotropin releasing factor provided dose-dependent neuronal protection with maximum recovery (37.95 +/- 8.71%) occurring at 10(-9) concentrations. The competitive antagonist alpha-CRF provided a similar degree of recovery at 10(-6) concentration, whereas 10(-9) molar concentration of competitive antagonist resulted in 16.84 +/- 7.68% recovery. CONCLUSIONS: Corticotropin releasing factor provides moderate protection to hypoxic hippocampal neurons in the brain slice preparation. The mechanism of action is unknown but appears to be a direct neuronal effect. These results support the hypothesis that corticotropin releasing factor may act as an endogenous neuroprotective hormone during hypoxia.

Animals↗

PubMed1993

Comparison of uptake and incorporation of docosahexaenoic and arachidonic acids by frog retinas.

Vertebrate retinas, especially photoreceptor cellular membranes, contain high levels of docosahexaenoic acid (DHA) and relatively low levels of arachidonic acid (AA). The present study was designed to test the hypothesis that DHA enrichment in the retina is the result of preferential uptake and incorporation relative to other fatty acids. Frog retinas were incubated in vitro with [3H]DHA or [3h]AA for up to 6 h, and the amounts of label in retinal lipids were quantitated. The incorporation of DHA into total lipids, triglycerides, phosphatidylcholine, and phosphatidylethanolamine was similar to that of AA when each was presented as the only substrate, and was linear with fatty acid concentration and incubation time. The addition of excess, unlabeled AA reduced the uptake and incorporation of DHA into retinal lipids. A slightly greater inhibition was noted for the uptake and incorporation of AA in the presence of unlabeled DHA. There was about 2-3 fold greater incorporation of DHA into phosphatidic acid, diglycerides, and phosphatidylinositol compared with AA, whereas the reverse was found for phosphatidylserine. The different levels of DHA and AA in retinal phospholipids cannot be explained by different rates of uptake and incorporation of these fatty acids into lipids, although some slight enrichment of DHA may be possible by this mechanism. The linear incorporation with fatty acid concentration suggests that the difference could be accomplished by controlling the amount and type of fatty acids delivered to the retina by the adjacent pigment epithelium.

Animals↗

PubMed1993

Inositol-1,4,5-trisphosphate receptors in the vertebrate retina.

Evidence has shown an activation of phosphatidylinositol 4,5-bisphosphate (PIP2) specific phospholipase C (PtdIns-PLC) by light in the vertebrate retina and rod outer segments (ROS), suggesting important roles for its two metabolites, 1,2-diacylglycerol (DG) and inositol-1,4,5-trisphosphate [Ins(1,4,5)P3]. DG activates protein kinase C (PKC) and Ins(1,4,5)P3 releases bound intracellular calcium. Since Ca2+ plays an important role in light adaptation, the presence of Ins(1,4,5)P3 receptors in ROS may indicate a regulatory role of Ins(1,4,5)P3 to the free Ca2+ content. In the present study, we investigated the Ins(1,4,5)P3 receptors in whole retinal membranes and several subcellular fractions prepared from bovine retinas. Scatchard analyses of binding data for retinal membrane preparations showed a single, high-affinity binding site with equilibrium dissociation constant (Kd) of 24 +/- 2 nM and maximal binding capacity (Bmax) of 353 +/- 15 fmol/mg protein at pH 7.4. Specific binding was found in both small and large synaptosomal preparations representing inner and outer plexiform layers, respectively. A detectable, but low abundance of Ins(1,4,5)P3-specific binding in ROS was observed at both pH 7.4 and 8.3, but no specific binding of Ins(1,4,5)P3 was found in isolated outer segment discs. The binding of Ins(1,4,5)P3 in ROS was reduced by addition of ATP, suggesting a regulatory role for this nucleotide. Addition of calcium, sodium, and potassium ions also reduced specific binding of Ins(1,4,5)P3. Immunocytochemical studies indicate intense staining in the inner segment and extending to the ROS. Inner and outer plexiform layers were also stained. These findings show that the Ins(1,4,5)P3 receptor is present in photoreceptor cells and inner and outer plexiform layers in the vertebrate retina.

Adenosine Triphosphate↗

PubMed1993

Visual discovery in mind and on paper.

The effectiveness of mental imagery with and without drawing support (perceptual assistance) in the visual synthesis of novel patterns was studied in three experiments. When the task was to create one recognizable pattern from three simple shapes in a 2-min assembly period, subjects were as likely to produce a recognizable or creative pattern per trial whether mental imagery was augmented by external drawing support or not. When the task was to create as many patterns as possible in a 3-min assembly period, more patterns were produced per trial with external drawing support than without; however, neither the recognizability nor the creativity of the patterns differed. Differences in performance in the visual synthesis task with and without external drawing support are interpreted in terms of limited cognitive resources.

Adult↗

PubMed1993

Differential incorporation of docosahexaenoic and arachidonic acids in frog retinal pigment epithelium.

Vertebrate retinas contain a high level of docosahexaenoic acid (DHA, 22:6n-3) and a relatively low level of arachidonic acid (AA, 20:4n-6). Although it is not known how DHA is selectively concentrated in the retina, the retinal pigment epithelium (RPE) is intimately involved in this process as these cells phagocytize shed rod outer segments (containing DHA) and take up DHA from the circulation. To explore the role of the RPE in the DHA enrichment in the retina, native frog RPE cells (RPE-eyecups) were incubated with [3H]DHA or [3H]AA for short times, or pulsed for up to 1 h with the two labeled fatty acids plus labeled glycerol simultaneously, followed by a chase for up to 7 h. The incorporation of label into various lipids was monitored by thin-layer or high performance liquid chromatography. In short-time incubations, a greater amount of DHA was incorporated into neutral lipids (primarily triglycerides, TG) compared with AA, while similar amounts of both fatty acids were found in phospholipids. On a relative basis, DHA was esterified mainly into TG, with AA into phospholipids. The uptake of each fatty acid correlated linearly with concentration (30-120 nM) and the incorporation pattern was distinct. Interestingly, the uptake and incorporation of labeled DHA or AA were not affected by the presence of unlabeled AA or DHA, respectively. In a pulse-chase experiment, RPE cells were active in the de novo synthesis of glycerolipids, particularly TG, which achieved a specific activity as high as diglycerides and ten times higher than the major phospholipids. The incorporation of DHA into most glycerolipids occurred to a large extent during de novo glycerolipid synthesis, whereas AA was incorporated mainly by deacylation-reacylation reactions. Our results suggest different metabolic pathways for handling DHA and AA in frog RPE. The preferential incorporation of DHA into TG suggests that TG might play an important role in the selective enrichment of DHA in the retina and in the recycling of photoreceptor DHA between the RPE and the retina.

Acylation↗

PubMed1993

National pathology manpower survey of 1991. Projected needs in community hospitals and private laboratory practice.

The third survey of a representative group of pathologists in community practice confirms the prediction based on the 1987 and 1988 surveys that there would be a growing deficit in the number of pathologists in this practice setting. There is an increasing number of reported vacancies in pathology groups and a significant increment in the percentage of older pathologists, with 32% being older than 54 years of age in 1991, compared with 25% in 1987. Projections based on the plan of individual respondents to retire and the anticipated changes in practice groups suggest that there will continue to be more pathologists leaving practice than new pathologists entering the specialty.

Adult↗

PubMed1993

Lipids of human retina, retinal pigment epithelium, and Bruch's membrane/choroid: comparison of macular and peripheral regions.

PURPOSE: To understand the difference between macular and peripheral regions, tissue samples of human retina, retinal pigment epithelium, and Bruch's membrane/choroid were dissected and analyzed for lipid composition. METHOD: To facilitate dissections and enhance the recovery of tissues, eyecups were prefixed for 1 hour in 10% formalin (pH 7). Lipids were extracted from 4-mm trephined punches of tissues and analyzed by high-performance liquid chromatography. After separation of neutral lipids and phospholipids, total fatty acids in both lipid classes were quantitated. RESULTS: The major phospholipid classes in retina, retinal pigment epithelium, and Bruch's membrane/choroid were phosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl inositol, and phosphatidyl serine; the major fatty acids were palmitic (16:0), stearic (18:0), and oleic (18:1). Although the three tissues had similar total fatty acid and phospholipid components, their relative compositions were different. Neutral lipid/phospholipid ratios in retinal pigment epithelium and Bruch's membrane/choroid were almost three times higher than in the retina. CONCLUSIONS: This study provides information about the lipid composition of macular and peripheral regions of the human retina, retinal pigment epithelium, and Bruch's membrane/choroid. The methodology employed enabled study of lipids in small amounts of tissue, which will be of value in investigating the biochemical aspects of age-related macular degeneration.

Adult↗

PubMed1993

A method for the isolation of retinal pigment epithelial cells from adult rats.

PURPOSE: Isolating retinal pigment epithelium (RPE) cells from adult rat was the goal of this study. METHOD: A modification of the procedure of Mayerson et al was the method employed. After the cornea and lens were removed, the eyecup was treated with hyaluronidase plus collagenase. The neural retina was carefully removed with little RPE attached. The eyecup, free of retina, was treated with the same enzyme cocktail that loosens any attached rod outer segments as well as the attachment of the RPE to Bruch's membrane. RPE cells were isolated in calcium-free medium as sheets of cells. RESULTS: Light and electron microscopy revealed good cell morphology. Purity of the RPE preparation was established by microscopy, polyacrylamide gel electrophoresis, and lipid analysis. The viability of the isolated RPE was about 74% by trypan blue exclusion test. CONCLUSIONS: This technique enables RPE to be isolated from adult rat in quantities sufficient for biochemical analysis.

Animals↗

PubMed1992

Activation of bovine rod outer segment phospholipase C by arrestin.

Phospholipase C (PLC) enzyme activity in rod outer segment (ROS) membranes bleached in the presence of ATP and GTP was assayed using exogenously added [3H]phosphatidylinositol 4,5-bisphosphate vesicles as substrate. The addition of the soluble ROS protein arrestin (also known as S-antigen or 48K protein) to ROS membranes activated PLC 2-3.4-fold. This activation was dose-dependent, and maximal activation was observed at an arrestin concentration of congruent to 110-220 nM. PLC activation by arrestin was dependent on ROS protein concentration and free Ca2+. Soluble PLC (s-PLC) enzyme activity present in hypotonic extracts of bleached ROS was also activated 2-4-fold by arrestin. Maximum activation of s-PLC by arrestin was observed at free Ca2+ of 80 nM. Arrestin activation of s-PLC was not affected by urea-treated and extensively washed ROS membranes, suggesting that rhodopsin was not required for the observed effect of arrestin on s-PLC. The results are indicative of a direct interaction of arrestin with s-PLC, resulting in the activation of the latter. Based on these results and the documented binding of arrestin to bleached and phosphorylated rhodopsin, a model for the light activation of PLC in ROS is proposed.

Animals↗

PubMed1992

Quantitation of phenacyl esters of retinal fatty acids by high-performance liquid chromatography.

A high-performance liquid chromatographic (HPLC) method for the separation and quantitation of retinal fatty acids containing long-chain polyunsaturated fatty acids is described. Fatty acids from frog retinal lipids were converted to the corresponding phenacyl derivatives which were separated on a C18 reversed-phase column and detected at 242 nm. Molar absorptivities (peak area units/nmol) of up to seventeen fatty acid phenacyl derivatives were determined and used for quantitation of fatty acids separated by HPLC. Compared with gas chromatography, the HPLC method gave a similar molar percent distribution of the fatty acids and was twenty to fifty times more sensitive. This HPLC method provides a useful means for the study of chemistry and metabolism of long-chain polyunsaturated fatty acids in retina and other tissues where amounts of material may be limited or recovery of individual components desirable.

Acetophenones↗