AMPA-preferring receptors mediate excitatory non-NMDA responses of primate retinal ganglion cells

Glutamate and kainate-induced currents of primate ganglion cells were studied using the whole-cell patch-clamp technique in a retinal slice preparation. Antagonists and allosteric modulators of desensitization selective for either alpha-amino-3-hydroxy-5-methyl-4-isoazoleprionic acid (AMPA)- or kainate-preferring receptors were used to determine the contributions of each type of receptor to excitatory responses. With synaptic transmission and NMDA receptors blocked, the AMPA-preferring receptor antagonist GYKI 52466 (30 microM-100 microM) reversibly blocked most of the glutamate-induced current in ganglion cells. GYKI 52466 also blocked the response in ganglion cells to focally applied kainate, suggesting that the current response to kainate arises from activation of AMPA-preferring receptors, and not kainate-preferring receptors. Both cyclothiazide (10 microM-100 microM) and the novel drug 4-[2-(phenylsulfonylamino)ethylthio]-2,6-difluoro-phenoxyacetamide (PEPA, 20 microM-100 microM), which selectively enhance responses mediated by AMPA-preferring receptors, enhanced glutamate-induced responses of ganglion cells. Since these drugs preferentially inhibit desensitization of the flip and flop splice variants, respectively, of AMPA-preferring receptors, it is likely that both splice variants are present on these ganglion cells. Concanavalin A, which selectively suppresses the desensitization of kainate-preferring receptors, had no effect on the glutamate-induced responses of ganglion cells. We conclude that the non-NMDA component of the excitatory, glutamatergic input to primate ganglion cells is mediated largely by AMPA-preferring receptors, with little, if any, kainate-preferring receptor-mediated response.

Head-column field-amplified sample stacking in capillary electrophoresis for the determination of cimetidine, famotidine, nizatidine, and ranitidine-HCl in plasma

In this study, low concentrations of histamine2-receptor (H2-)antagonists were effected across a water plug, with separation taking place in a binary buffer comprising ethylene glycol and NaH2PO4 (pH 5.0), and detection at 214 nm. Liquid-liquid extraction with ethyl acetate- isopropanol is shown to provide extracts that are sufficiently clean. The calibration curves were linear over a concentration range of 0.1-2.00 microg/mL cimetidine, 0.2-5.0 microg/mL ranitidine-HCl, 0.3-5.0 microg/mL nizatidine, and 0.1-3.0 microg/mL famotidine. Mean recoveries were > 82%, while the intra- and interday relative standard deviations (RSDs) and relative errors (REs) were all < 13%. The method is sensitive with a detection limit of 3 ng/mL cimetidine, 30 ng/mL ranitidine HCl, 50 ng/mL nizatidine and 10 ng/mL famotidine (S/N = 3, electric-driven injection 90 s). This newly developed capillary electrophoresis (CE) method was applied for the determination of analytes extracted from plasma taken from a volunteer dosing a cimetidine, ranitidine, and nizatidine tablet simultaneously. These three H2-antagonists can be detected in real samples by this method, excluding the low dosing of famotidine tablet.

Simultaneous determination of cimetidine, famotidine, nizatidine, and ranitidine in tablets by capillary zone electrophoresis

A simple capillary zone electrophoresis (CZE) method is described for the simultaneous determination of cimetidine (CIM), famotidine (FAM), nizatidine (NIZ), and ranitidine (RAN). The analysis of these drugs was performed in a 100 mM phosphate buffer, pH 3.5. Several parameters were studied, including wavelength for detection, concentration and pH of phosphate buffer, and separation voltage. The quantitative ranges were 100-1,000 microM for each analyte. The intra- and interday relative standard deviations (n = 5) were all less than 4%. The detection limits were found to be about 10 microM for CIM, 20 microM for RAN, 20 microM for NIZ, and 10 microM for FAM (S/N = 3, injection 1 s) at 214 nm. All recoveries were greater than 92%. Applications of the method to the assay of these drugs in tablets proved to be feasible.

alpha(2)-Macroglobulin from rheumatoid arthritis synovial fluid: functional analysis defines a role for oxidation in inflammation

A hallmark of inflammation is the release of oxidants, proteinases, and cytokines, all important mediators of the inflammatory cascade. alpha(2)-Macroglobulin (alpha(2)M) is a high-affinity, broad-specificity proteinase inhibitor that also binds and regulates the biological activities of a number of cytokines. We demonstrated recently that hypochlorite-oxidized alpha(2)M has decreased ability to inhibit proteinases and regulate cytokines in vitro. The role of oxidation in regulating alpha(2)M functions in vivo is largely unknown. To determine the extent and biological consequence of in vivo alpha(2)M oxidation, we measured the degree of oxidative alpha(2)M modification from rheumatoid arthritis (RA) synovial fluid and compared this with osteoarthritis (OA) as noninflammatory controls. We found that RA synovial fluid alpha(2)M is significantly more oxidized than that from OA. RA synovial fluid also contains a twofold higher median alpha(2)M level than OA, while having only half the alpha(2)M-proteinase inhibitory activity. Detailed biochemical analysis demonstrates proteolytically degraded alpha(2)M in RA greater than in OA synovial fluid. Additionally, the hypochlorite-mediated oxidation product, chlorotyrosine, is present in RA more than in OA or plasma alpha(2)M samples. Taken together, these findings confirm a role for oxidative regulation of inflammation by altering the functions of extracellular mediators such as alpha(2)M.

Differential regulation of the fibroblast growth factor (FGF) family by alpha(2)-macroglobulin: evidence for selective modulation of FGF-2-induced angiogenesis

The fibroblast growth factor (FGF) family has an important role in processes such as angiogenesis, wound healing, and development in which precise control of proteinase activity is important. The human plasma proteinase inhibitor alpha(2)-macroglobulin (alpha(2)M) regulates cellular growth by binding and modulating the activity of many cytokines and growth factors. These studies investigate the ability of native and activated alpha(2)M (alpha(2)M*) to bind to members of the FGF family. Both alpha(2)M and alpha(2)M* bind specifically and saturably to FGF-1, -2, -4, and -6, although the binding to alpha(2)M* is of significantly higher affinity. Neither alpha(2)M nor alpha(2)M* bind to FGF-5, -7, -9, or -10. FGF-2 was chosen for more extensive study in view of its important role in angiogenesis. It was demonstrated that FGF-2 binds to the previously identified TGF-beta binding site. The alpha(2)M* inhibits FGF-2-dependent fetal bovine heart endothelial cell proliferation in a dose-dependent manner. Unexpectedly, alpha(2)M* does not affect FGF-2-induced vascular tubule formation on Matrigel basement membrane matrix or collagen gels. Further studies demonstrate that FGF-2 partitions between fluid-phase alpha(2)M* and solid-phase Matrigel or collagen. These studies suggest that the ability of alpha(2)M* to modulate the activity of FGF-2 is dependent on an interplay with extracellular matrix components. (Blood. 2001;97:3450-3457)

Immunocytochemical analysis of cholinergic amacrine cells in the tiger salamander retina

Cholinergic amacrine cells in the tiger salamander retina were observed for the first time by using antibodies against choline acetyltransferase (ChAT). ChAT-immunoreactive cells were present in the inner nuclear layer (INL) and in the ganglion cell layer (GCL), and the somas of the former population (average diameter = 15.13 microm) were slightly smaller than those of the latter population (average diameter = 16.42 microm). The processes of these cells form two distinct narrow bands in the inner plexiform layer (IPL), one located near 0.2 inner plexiform units (IU) and the other near 0.65-0.7 IU. Soma size, cell density and spatial distribution of ChAT-positive cells were quantitatively analyzed. Our results suggest that cholinergic amacrine cells in the salamander retina are very similar to their counter parts in other species, and they can be used as a model system for studying cholinergic functions in the visual system.

Apoptotic cell death of cultured salamander photoreceptors induced by cccp: CsA-insensitive mitochondrial permeability transition

Photoreceptor degeneration is mediated by apoptosis in several animal models, although the underlying mechanisms are yet to be elucidated. We present here an apoptotic model based on a primary cell culture of tiger salamander photoreceptors, in which treatment with carbonyl cyanide m-chlorophenylhydrazone (cccp), a protonophore, induced apoptosis. Cells exposed to cccp showed condensed nuclei and displayed positive TdT-dUTP terminal nick-end labeling (TUNEL). In addition, 10–100 microM cccp rapidly induced a reduction of Delta psi(m) and &gt; or = 30 microM cccp induced a significant leakage of calcein from mitochondria to cytosol and nucleus, indicating a change in mitochondrial inner membrane permeability. Cyclosporin A (CsA), a transition pore blocker, did not prevent the cccp-induced MPT or the cccp-evoked apoptotic cell death, suggesting that cccp-induced apoptotic process was mediated by a CsA-insensitive pathway. This cell model provides an in vitro tool for studying mechanisms of photoreceptor apoptosis in isolated photoreceptors and may provide clues to the etiology of retinal degeneration.

Delta-aminolevulinate dehydratase polymorphism and blood lead levels in Chinese children

This study investigated the relationship between the delta-aminolevulinate dehydratase (ALAD) isozymes and the blood lead levels of Chinese children. The purpose of this study was to determine the precise ALAD genotyping in Chinese children and identify the contribution of the ALAD genotype to the body lead burden. Blood samples were obtained from 109 boys and 120 girls. These children were 6-10 years old and from a single primary school. Both the school and their homes were within a community in which a large smelter was located. An environmental questionnaire was obtained for each subject, and blood lead levels and ALAD isozyme phenotype were analyzed in a double-blinded fashion. The blood lead levels of 229 children ranged from 4.5 to 26.4 microg/dl; the mean was 10.3 microg/dl and the standard deviation was 3.3 microg/dl. The gene distribution of the ALAD isozyme phenotypes in these environmentally exposed children was ALAD 1-1 (92%), ALAD 1-2, (8%), and ALAD 2-2 (0%). The mean blood level of the environmentally exposed children, who were homozygous for the ALAD1 allele, was 9.7 microg/dl; the mean for those who were heterozygous for the ALAD2 allele was 11.7 microg/dl. Using the t test, the means of the groups were different at the level of t=2.2058, P<0.05. Step-wise regression and multiple analyses of covariance were employed to control the confounders to measuring the independent contribution of the ALAD genotype on blood lead levels. After controlling the confounders, the contribution of the ALAD genotype to the blood lead level was greater and still statistically significant (F=7.3201, P<0.01). These results indicate that individuals carrying the ALAD2 allele are more likely to have sustained increases in blood lead levels when exposed to a lead-contaminated environment.

Expression and characterization of the naturally occurring mutation L394R in human gamma-glutamyl carboxylase

Patients with mutation L394R in gamma-glutamyl carboxylase have a severe bleeding disorder because of decreased biological activities of all vitamin K-dependent coagulation proteins. Vitamin K administration partially corrects this deficiency. To characterize L394R, we purified recombinant mutant L394R and wild-type carboxylase expressed in baculovirus-infected insect cells. By kinetic studies, we analyzed the catalytic activity of mutant L394R and its binding to factor IX's propeptide and vitamin KH(2). Mutant L394R differs from its wild-type counterpart as follows: 1) 110-fold higher K(i) for Boc-mEEV, an active site-specific, competitive inhibitor of FLEEL; 2) 30-fold lower V(max)/K(m) toward the substrate FLEEL in the presence of the propeptide; 3) severely reduced activity toward FLEEL carboxylation in the absence of the propeptide; 4) 7-fold decreased affinity for the propeptide; 5) 9-fold higher K(m) for FIXproGla, a substrate containing the propeptide and the Gla domain of human factor IX; and 6) 5-fold higher K(m) for vitamin KH(2). The primary defect in mutant L394R appears to be in its glutamate-binding site. To a lesser degree, the propeptide and KH(2) binding properties are altered in the L394R mutant. Compared with its wild-type counterpart, the L394R mutant shows an augmented activation of FLEEL carboxylation by the propeptide.

The conformation-dependent interaction of alpha 2-macroglobulin with vascular endothelial growth factor. A novel mechanism of alpha 2-macroglobulin/growth factor binding

alpha(2)-Macroglobulin (alpha(2)M) is a highly conserved proteinase inhibitor present in human plasma at high concentration (2-4 mg/ml). alpha(2)M exists in two conformations, a native form and an activated, receptor-recognized form. While alpha(2)M binds to numerous cytokines and growth factors, in most cases, the nature of the alpha(2)M interaction with these factors is poorly understood. We examined in detail the interaction between alpha(2)M and vascular endothelial growth factor (VEGF) and found a novel and unexpected mechanism of interaction as demonstrated by the following observations: 1) the binding of VEGF to alpha(2)M occurs at a site distinct from the recently characterized growth factor binding site; 2) VEGF binds different forms of alpha(2)M with distinct spatial arrangement, namely to the interior of methylamine or ammonia-treated alpha(2)M and to the exterior of native and proteinase-converted alpha(2)M; and 3) VEGF (molecular mass approximately 40 kDa) can access the interior of receptor-recognized alpha(2)M in the absence of a proteinase trapped within the molecule. VEGF bound to receptor-recognized forms of alpha(2)M is internalized and degraded by macrophages via the alpha(2)M receptor, the low density lipoprotein receptor-related protein. Oxidation of both native and receptor-recognized alpha(2)M results in significant inhibition of VEGF binding. We also examined the biological significance of this interaction by studying the effect of alpha(2)M on VEGF-induced cell proliferation and VEGF-induced up-regulation of intracellular Ca(2+) levels. We demonstrate that under physiological conditions, alpha(2)M does not impact the ability of VEGF to induce cell proliferation or up-regulate Ca(2+).

Morphological and electrophysiological properties of dissociated primate retinal cells

Although isolated retinal cell preparations have been used widely to study retinal function in lower vertebrates, dissociated cells from primate retina have not been developed for routine physiological experiments. In this study, we demonstrated the feasibility of obtaining viable and identifiable dissociated cells from the primate retina. In addition, we characterized voltage-dependent membrane currents in each type of primate retinal cell with the whole-cell patch-clamp technique. Multiple types of ionic conductance with distinctive current profiles were recorded in various types of primate retinal neurons. Photoreceptors exhibited an inward I(H) activated by membrane hyperpolarization and an outward current activated at depolarized potentials. Two types of potassium currents (transient potassium current, I(K(A)), and delayed rectifier potassium current, I(K(V))) were recorded from bipolar cells. I(K(A)) dominated the current response in putative midget bipolar cells, and I(K(V)) was mainly associated with putative rod bipolar cells. L-type calcium currents (I(Ca)) were observed in primate bipolar cells with axon terminals, but not in axotomized bipolar cells. Large voltage-dependent sodium currents (I(Na)) were only recorded from ganglion cells. Muller cells exhibited I(K(V)) and large potassium inward rectifier current (I(K(IR))), and occasionally a small I(Na). Neurons with electrophysiological signatures of amacrine cells and horizontal cells were also studied even though their morphological features were lost during cell dissociation. By using both morphological and physiological criteria outlined in this report, it is possible to use the dissociated retinal cell preparation as an in vitro system for physiological, biochemical and pharmacological studies of the primate visual system.

Metallothionein induction in early larval stages of tilapia (Oreochromis mossambicus)

Amounts of whole-body metallothionein (MT) in tilapia (Oreochromis mossambicus) larvae increased to a peak (1,500 ng mg(-1) protein) 1 d after hatching (H1), decreased rapidly thereafter, and was maintained at a constant level (700 ng mg(-1)) 3 d after hatching (H3). Waterborne Cd(2+) could stimulate MT expression in newly hatched (H0) larvae in dose-dependent and time-dependent patterns. H0 larvae, which were treated with 35 microg L(-1) Cd(2+) for 24 h, showed a 1.7-fold increase in the MT amount (174.0+/-64.7) and a 6. 5-fold increase in accumulated Cd(2+) but no significant change in Ca(2+) content, compared with the H0 control (MT, 102.6+/-48.1). H3 larvae with the same treatment revealed about a 10-fold increase in accumulated Cd(2+), a 10% decrease in Ca(2+) content, but no change in MT (261.2+/-120.0), compared with the H3 control (MT, 330+/-74.0). H0 larvae could synthesize more MT to bind Cd(2+) for detoxification in 35 microg L(-1) Cd(2+), a dose that would not affect normal physiology or survival of H0 larvae. On the other hand, 35 microg L(-1) Cd(2+) caused H3 larvae to experience hypocalcemia, an abnormal physiological condition, in which H3 larvae could not synthesize sufficient MT, thus causing greater than 25% mortality. These results indicate for the first time that the inducibility of MT by waterborne Cd(2+) is development dependent, being correlated with inconsistent sensitivities to Cd(2+) during larval development.

A topological study of the human gamma-glutamyl carboxylase

gamma-Glutamyl carboxylase (GC), a polytopic membrane protein found in the endoplasmic reticulum (ER), catalyzes vitamin K-dependent posttranslational modification of glutamate to gamma-carboxyl glutamate. In an attempt to delineate the structure of this important enzyme, in vitro translation and in vivo mapping were used to study its membrane topology. Using terminus-tagged full-length carboxylase, expressed in 293 cells, it was demonstrated that the amino-terminus of the GC is on the cytoplasmic side of the ER, while the carboxyl-terminus is on the lumenal side. In addition, a series of fusions were made to encode each predicted transmembrane domain (TMD) followed by a leader peptidase (Lep) reporter tag, as analyzed by the computer algorithm TOPPRED II. Following in vitro translation of each fusion in the presence of canine microsomes, the topological orientation of the Lep tag was determined by proteinase K digestion and endoglycosidase H (Endo H) cleavage. From the topological orientation of the Lep tag in each fusion, the GC spans the ER membrane at least 5 times, with its N-terminus in the cytoplasm and its C-terminus in the lumen.

Polymorphisms in the coding exons of the human luteinizing hormone receptor gene. Mutations in brief no. 124. Online

Four polymorphisms were identified in the coding exons of the human luteinizing hormone/chorionic gonadotropin receptor (hLHR) gene. A CTGCAG insertion occurred after nucleotide 54 in 8 of 34 independent chromosomes examined. The heterozygosity frequency was 0.353. This Leu-Gln dipeptide insertion in the first Leucine repeat of the hLHR extracellular domain did not affect the ligand binding affinity of the receptor. Among the 54 chromosomes analyzed, 64.8% was A and 35.2% was G at nucleotide 872 in exon 10. The heterozygosity frequency was 0.115. The A/G substitution led to the replacement of Asn by Ser in the G allele and the abolition of a potential N-glycosylation site. Another polymorphism occurred at nucleotide 935. Fifty nine percent of chromosomes examined were A and 41% were G at this site with the encoded amino acid being Ser in the former and Asn in the latter. The heterozygosity frequency was 0.192. This polymorphism did not have biological consequence. Both of the exon 10 polymorphisms showed ethnic prevalence with the 872 G allele and 935 A allele predominantly in non-Caucasians. The fourth polymorphism was neutral and occurred at nucleotide 1065 in exon 11, with C in 60% and T in 40% of the 50 chromosomes examined. These polymorphisms are useful for tracking the inheritance of specific hLHR allele.

Functional architecture of synapses in the inner retina: segregation of visual signals by stratification of bipolar cell axon terminals

We correlated the morphology of salamander bipolar cells with characteristics of their light responses, recorded under voltage-clamp conditions. Twelve types of bipolar cells were identified, each displaying a unique morphology and level(s) of axon terminal stratification in the inner plexiform layer (IPL) and exhibiting light responses that differed with respect to polarity, kinetics, the relative strengths of rod and cone inputs, and characteristics of spontaneous EPSCs (sEPSCs) and IPSCs. In addition to the well known segregation of visual information into ON and OFF channels along the depth of the IPL, we found an overlying mapping of spectral information in this same dimension, with cone signals being transmitted predominantly to the central IPL and rod signals being sent predominantly to the margins of the IPL. The kinetics of bipolar cell responses correlated with this segregation of ON and OFF and of rod and cone information in the IPL. At light offset, rod-dominated cells displayed larger slow cationic current tails and smaller rapid overshoot responses than did cone-dominated cells. sEPSCs were generally absent in depolarizing bipolar cells but present in all hyperpolarizing bipolar cells (HBCs) and larger in rod-dominated HBCs than in cone-dominated HBCs. Inhibitory chloride currents, elicited both at light onset and light offset, tended to be larger for cone-dominated cells than for rod-dominated cells. This orderly segregation of visual signals along the depth of the IPL simplifies the integration of visual information in the retina, and it begins a chain of parallel processing in the visual system.

Prevalence of SHV-12 among clinical isolates of Klebsiella pneumoniae producing extended-spectrum beta-lactamases and identification of a novel AmpC enzyme (CMY-8) in Southern Taiwan

Twenty (8.5%) of 234 nonrepetitive clinical isolates of Klebsiella pneumoniae from southern Taiwan were found to produce extended-spectrum beta-lactamases (ESBLs): 10 strains produced SHV-12, 4 produced SHV-5, 2 produced a non-TEM non-SHV ESBL with a pI of 8.3, 3 produced a novel AmpC beta-lactamase designated CMY-8 with a pI of 8.25, and 1 produced SHV-12 and an unidentified AmpC enzyme with a pI of 8.2. The CMY-8 enzyme confers a resistance phenotype similar to CMY-1 and MOX-1, and sequence comparisons showed high homologies (>95%) of nucleotide and amino acid sequences among these three enzymes. Plasmid and pulse-field gel electrophoresis analyses revealed that all isolates harboring an SHV-derived ESBL were genetically unrelated, indicating that dissemination of resistance plasmids is responsible for the spread of SHV ESBLs among K. pneumoniae in this area. All three isolates carrying CMY-8 had identical genotypic patterns, suggesting the presence of an epidemic strain.

I4AA-Sensitive chloride current contributes to the center light responses of bipolar cells in the tiger salamander retina

Light-evoked currents in depolarizing and hyperpolarizing bipolar cells (DBCs and HBCs) were recorded under voltage-clamp conditions in living retinal slices of the larval tiger salamander. Responses to illumination at the center of the DBCs' and HBCs' receptive fields were mediated by two postsynaptic currents: DeltaI(C), a glutamate-gated cation current with a reversal potential near 0 mV, and DeltaI(Cl), a chloride current with a reversal potential near -60 mV. In DBCs DeltaI(C) was suppressed by L-2-amino-4-phosphonobutyric acid (L-AP4), and in HBCs it was suppressed by 6,7-dinitroquinoxaline-2,3-dione (DNQX). In both DBCs and HBCs DeltaI(Cl) was suppressed by imidazole-4-acetic acid (I4AA), a GABA receptor agonist and GABA(C) receptor antagonist. In all DBCs and HBCs examined, 10 microM I4AA eliminated DeltaI(Cl) and the light-evoked current became predominately mediated by DeltaI(C). The addition of 20 microM L-AP4 to the DBCs or 50 microM DNQX to HBCs completely abolished DeltaI(C). Focal application of glutamate at the inner plexiform layer elicited chloride currents in bipolar cells by depolarizing amacrine cells that release GABA at synapses on bipolar cell axon terminals, and such glutamate-induced chloride currents in DBCs and HBCs could be reversibly blocked by 10 microM I4AA. These experiments suggest that the light-evoked, I4AA-sensitive chloride currents (DeltaI(Cl)) in DBCs and HBCs are mediated by narrow field GABAergic amacrine cells that activate GABA(C) receptors on bipolar cell axon terminals. Picrotoxin (200 microM) or (1,2,5,6-tetrahydropyridine-4yl) methyphosphinic acid (TPMPA) (2 other GABA(C) receptor antagonists) did not block (but enhanced and broadened) the light-evoked DeltaI(Cl), although they decreased the chloride current induced by puff application of GABA or glutamate. The light response of narrow field amacrine cells were not affected by I4AA, but were substantially enhanced and broadened by picrotoxin. These results suggest that there are at least two types of GABA(C) receptors in bipolar cells: one exhibits stronger I4AA sensitivity than the other, but both can be partially blocked by picrotoxin. The GABA receptors in narrow field amacrine cells are I4AA insensitive and picrotoxin sensitive. The light-evoked DeltaI(Cl) in bipolar cells are mediated by the more strongly I4AA-sensitive GABA(C) receptors. Picrotoxin, although acting as a partial GABA(C) receptor antagonist in bipolar cells, does not suppress DeltaI(Cl) because its presynaptic effects on amacrine cell light responses override its antagonistic postsynaptic actions.

Effect of heparin reversal and fresh platelet transfusion on platelet emboli post-cardiopulmonary bypass in a pig model

Heparin reversal by protamine and fresh platelet transfusion may decrease bleeding complications post-cardiopulmonary bypass (CPB) and may increase the level of organ trapped platelet emboli. Platelet emboli were quantified in two groups of 12 Yorkshire pigs (30-35 kg), where 111indium labeled autologous platelets (INPLT: 850-1,200 microCi) were injected intravenously before and after CPB (BCPB, ACPB), and the platelet emboli level in intact organs and their samples (brain, heart, kidneys, lung, liver, and spleen) was quantified with an ion chamber and a gamma counter, respectively. All pigs were systemically heparinized (ACT > 400 sec). CPB was carried out at 2.5-3.5 L/min at 28 degrees C using a centrifugal pump, an oxygenator (OX:Bentley Univox 1.8 m2), an arterial filter (AF:0.25 m2), and a cardiotomy reservoir (CR: BMR 250) for 90 min. Heparin was reversed with an equivalent dose of protamine. The percent of INPLT dose (ID%, mean +/- SD) in organs of BCPB and ACPB pigs was calculated. The sequence of platelet emboli on a unit weight basis (ID%/g) had the following order: Spleen > Liver > Lung > Kidneys > Heart > Brain. The presence of significantly higher levels of emboli in brain, heart, and kidneys in the ACPB than the BCPB group suggest that platelet transfusion after heparin reversal with protamine may increase the risk of platelet emboli. However, it is an acceptable risk for patients having bleeding complications post-CPB.

Luteinizing hormone receptor mutations in disorders of sexual development and cancer

Human male sexual development is regulated by chorionic gonadotropin (CG) and luteinizing hormone (LH). Aberrant sexual development caused by both activating and inactivating mutations of the human luteinizing hormone receptor (LHR) have been described. All known activating mutations of the LHR are missense mutations caused by single base substitution. The most common activating mutation is the replacement of Asp-578 by Gly due to the substitution of A by G at nucleotide position 1733. All activating mutations are present in exon 11 which encodes the transmembrane domain of the receptor. Constitutive activity of the LHR causes LH releasing hormone-independent precocious puberty in boys and the autosomal dominant disorder familial male-limited precocious puberty (FMPP). Both germline and somatic activating mutations of the LHR have been found in patients with testicular tumors. Activating mutations have no effect on females. The molecular genetics of the inactivating mutations of the LHR are more variable and include single base substitution, partial gene deletion, and insertion. These mutations are not localized and are present in both the extracellular and transmembrane domain of the receptor. Inactivation of the LHR gives rise to the autosomal recessive disorder Leydig cell hypoplasia (LCH) and male hypogonadism or male pseudohermaphroditism. Severity of the clinical phenotype in LCH patients correlates with the amount of residual activity of the mutated receptor. Females are less affected by inactivating mutation of the LHR. Symptoms caused by homozygous inactivating mutation of the LHR include polycystic ovaries and primary amenorrhea.

Effects of betaxolol on light responses and membrane conductance in retinal ganglion cells

PURPOSE

To examine the physiological effects of betaxolol, a beta1-adrenergic receptor blocker commonly used in the treatment of glaucoma, on retinal ganglion cells and to evaluate its potential to elicit responses consistent with a neuroprotective agent against ganglion cell degeneration.

METHODS

Single-unit extracellular recording, electroretinogram (ERG), intracellular and whole-cell patch-clamp recording techniques were made from flatmounted, isolated retina, superfused eyecup, and living retinal slice preparations of the larval tiger salamander.

RESULTS

Bath application of 20 microM betaxolol reduced the glutamate-induced increase of spontaneous spike rate in retinal ganglion cell by approximately 30%. The glutamate-induced postsynaptic current recorded under voltage-clamp conditions was reduced by 50 microM betaxolol, and the difference current-voltage (I-V) relation (I(Control)-I(betaxolol)) was N-shaped and AP5-sensitive, characteristic of N-methyl-D-aspartate receptor-mediated current. Application of 50 microM betaxolol reversibly reduced the voltage-gated sodium and calcium currents by approximately one third of their peak amplitudes. The times-to-action of betaxolol on ganglion cells are long (15-35 minutes for 20-50 microM betaxolol), indicative of modulation through slow biochemical cascades. Betaxolol, up to 100 microM, exerted no effects on horizontal cells or the ERG, suggesting that the primary actions of this beta1 blocker are restricted to retinal ganglion cells.

CONCLUSIONS

These physiological experiments provide supporting evidence that betaxolol acts in a manner consistent with preventing retinal ganglion cell death induced by elevated extracellular glutamate or by increased spontaneous spike rates under pathologic conditions. The physiological actions of betaxolol lead to reducing neurotoxic effects in ganglion cells, which are the most susceptible retinal neurons to glutamate-induced damages under ischemic and glaucomatous conditions. Therefore, betaxolol has the potential to be a neuroprotective agent against retinal degeneration in patients with disorders mediated by such mechanisms.

Down-regulation by extracellular ATP of rat hepatocyte organic anion transport is mediated by serine phosphorylation of oatp1

Recent studies implicate a role in hepatocyte organic anion transport of a plasma membrane protein that has been termed oatp1 (organic anion transport protein 1). Little is known regarding mechanisms by which its transport activity is modulated in vivo. In previous studies (Campbell, C. G., Spray, D. C., and Wolkoff, A. W. (1993) J. Biol. Chem. 268, 15399-15404), we demonstrated that hepatocyte uptake of sulfobromophthalein was down-regulated by extracellular ATP. We have now found that extracellular ATP reduces the V(max) for transport of sulfobromophthalein by rat hepatocytes; K(m) remains unaltered. Reduced transport also results from incubation of hepatocytes with the phosphatase inhibitors okadaic acid and calyculin A. Immunoprecipitation of biotinylated cell surface proteins indicates that oatp1 remains on the cell surface after exposure of cells to ATP or phosphatase inhibitor, suggesting that loss of transport activity is not caused by transporter internalization. Exposure of (32)P-loaded hepatocytes to extracellular ATP results in serine phosphorylation of oatp1 with the appearance of a single major tryptic phosphopeptide; oatp1 from control cells is not phosphorylated. This phosphopeptide comigrates with one of four phosphopeptides resulting from incubation of cells with okadaic acid. These studies indicate that the phosphorylation state of oatp1 must be an important consideration when assessing alterations of its functional expression in pathobiological states.

Reduction of Platelet Thrombi and Emboli by L-Arginine during Cardiopulmonary Bypass in a Pig Model

We wanted to test the hypothesis that NO generation by L-arginine (LA) infusion will be beneficial in increasing blood flow to all organs to counteract the process of global ischemia during cardiopulmonary bypass (CPB) and to reduce platelet emboli by platelet inhibition. The effect of LA infusion on NO formation, vasodilation, and reduction of thromboembolic burden in organs and tissues after CPB was quantified with In-111-labeled autologous platelets in two major groups: 180 minutes CPB (CPB) and 90 minutes CPB plus 90 minutes reperfusion (RP). Platelets labeled with In-111 tropolone (650-780 µCi) were administered 24 hours before CPB and LA infusion (bolus, 10 mg/kg and infusion at 2 mg/kg/min, 21 pigs for 180 minutes CPB) in 8 groups of 30 Yorkshire pigs (30-35 kg, 6 pigs; LA 2 mg/kg/min, 3 pigs; sham-thoracotomy control, 6 pigs; unoperated control, 6 pigs). Two groups of 9 pigs (control CPB, 6 pigs; LA 2 mg/kg/min, 3 pigs) underwent 90 minutes of CPB and 90 minutes of reperfusion. All pigs were heparinized (ACT > 400 seconds); CPB was instituted with a roller pump, an oxygenator (OX: Bentley Univox, 1.8 m2), and an arterial filter (AF: 0.25 m2, Bentley) at a blood flow of 2.5-3.5 l/min. Radioactive thrombi in OX and AF and emboli in viscera, brain, and connective tissues were imaged with a gamma camera and were finally measured with an ion chamber and a gamma counter. The percent of injected platelets (mean +/- SD) in the organs and tissues of all pigs was calculated. Cerebral emboli were mapped in 25 regions of both hemispheres of pig brain. Flow cytometry with antibodies to CD61 (GPIIIa) and CD62P (GMP-140:control) of porcine platelets was carried out with blood samples taken before, during, and after CPB. Coronary bypass with LA infusion decreased the amount of adherent thrombi in OX and AF (p < 0.07). The embolic burden in brain and lung also decreased. Regional cerebral mapping of In-111 platelets showed reduced emboli in almost all regions, including the medulla, hip pocampus, and posterior cerebral cortex in both LA-treated groups. Flow cytometry of blood samples demonstrated the shift of equilibria from single platelet to platelet-aggregate-microparticle during CPB and steady-state level after the first 5-10 minutes of initiation of CPB. The L-arginine infusion reduced thrombi and emboli during CPB in the pig model.

Glutamate receptors differ in rod- and cone-dominated off-center bipolar cells

The axon morphology of off-center bipolar cells in salamander retinal slices was correlated with light responses and dendritic glutamate responses of these cells under voltage clamp. Cells with telodendria ramifying exclusively in the distal one-quarter of the inner plexiform layer were rod dominated, whereas cells with more centrally ramifying telodendria were cone dominated. The glutamate responses of the centrally ramifying cells displayed more apparent desensitization and a smaller underlying single channel conductance (1.2+/-0.3 pS) than did the distally ramifying cells (2.8+/-0.4 pS), although the responses for both classes of cells were strongly enhanced by cyclothiazide. These results suggest that different subtypes of AMPA receptors are present on rod- and cone-dominated cells, and that these may differ with respect to desensitization kinetics.