Age-related changes of aqueous protein profiles in rat fast and slow twitch skeletal muscles

Two-dimensional electrophoresis was used to generate the aqueous protein expression patterns of rat extensor digitorum longus muscle (EDL, fast twitch muscle) and solues muscle (SOL, slow twitch muscle) of different ages. Two specific protein spots, S1 and S3, were identified from EDL muscles at the ages of 12 and 18 months onward respectively. In the EDL muscles of aged rat (24 months) after intensive exercise training, S3 was still detected while S1 disappeared. In addition, diaphragm muscle (DIA, fast twitch muscle), which retains physically active throughout the life span, was used as nondisuse control. The results showed that the expressions of S1 and S3 in 24-month DIA muscle were identical with the trained aged EDL muscle. It is suggested that exercise might delay the onset of S1 expression. However, the expression of S3 over age seemed to be progressive and exercise independent. Another protein spot, S2 was identified to express only in young EDL and SOL muscles, but its expression decreased over age. Furthermore, exercise has no effect on S2 expression since S2 could not be detected in aged DIA as well as trained aged EDL and SOL muscles. These results indicated that aqueous protein expression patterns of skeletal muscle undergo changes during aging. Some of these changes such as S2 and S3 appear progressively, and some such as S1 could be delayed by exercise. S3 was identified as ubiquitin, which might play an important role in protein degradation during skeletal muscle aging process.

Spectral bifurcations in dispersive wave turbulence

Dispersive wave turbulence is studied numerically for a class of one-dimensional nonlinear wave equations. Both deterministic and random (white noise in time) forcings are studied. Four distinct stable spectra are observed-the direct and inverse cascades of weak turbulence (WT) theory, thermal equilibrium, and a fourth spectrum (MMT; Majda, McLaughlin, Tabak). Each spectrum can describe long-time behavior, and each can be only metastable (with quite diverse lifetimes)-depending on details of nonlinearity, forcing, and dissipation. Cases of a long-live MMT transient state dcaying to a state with WT spectra, and vice-versa, are displayed. In the case of freely decaying turbulence, without forcing, both cascades of weak turbulence are observed. These WT states constitute the clearest and most striking numerical observations of WT spectra to date-over four decades of energy, and three decades of spatial, scales. Numerical experiments that study details of the composition, coexistence, and transition between spectra are then discussed, including: (i) for deterministic forcing, sharp distinctions between focusing and defocusing nonlinearities, including the role of long wavelength instabilities, localized coherent structures, and chaotic behavior; (ii) the role of energy growth in time to monitor the selection of MMT or WT spectra; (iii) a second manifestation of the MMT spectrum as it describes a self-similar evolution of the wave, without temporal averaging; (iv) coherent structures and the evolution of the direct and inverse cascades; and (v) nonlocality (in k-space) in the transferral process.

[A method for preparation of carbon fiber electrode]

Carbon fiber electrode (CFE) can be used in detection of exocytosis of single neuron or endocrine cell. A simplified method for preparation of CFE, as described in the present paper, greatly ensures the coordination and success of the preparation. Such CFEs have a low noise level. Exocytosis of rat adrenal chromaffin cells was investigated in the clarification of the effect of MPP+ on transmitter release. It is found that exocytosis was not stimulated by MPP+ and the high K+ induced secretion was not changed by MPP+. These observations suggest that the previously reported elevation of dopamine content in the surrounding histosolution of DA neuron is probably resulted from blockage of the re-uptake of DA by MPP+.

Isolation of a gene from Arabidopsis thaliana related to nematode feeding structures

Using a promoter tagging approach, a gene upregulated in nematode feeding structures (NFS) of Heterodera schachtii was identified in Arabidopsis thaliana plants. Sequence analysis of the transgenic line bearing gus reporter gene and the wild-type plant revealed that the T-DNA had been inserted into the promoter of the gene, however, with transcription start points at different sites for the gus reporter gene and for the endogenous gene. This tagged gene, designated pyk20, encodes a transcript of 2.6 kb. Southern blot analysis revealed a single gene copy for pyk20 in the Arabidopsis C-24 genome. Other cruciferous plants were shown to possess pyk20 or homologous genes. The predicted amino acid sequence of the PYK20 protein contains 695 residues with a molecular mass of 78 kDa and includes a glutamine-rich domain in the C-terminal region. IAA and kinetin treatment increased the level of the pyk20 transcript in the plant, whereas ABA treatment and temperature stress reduced the pyk20 transcript level. In-situ hybridisation and Northern blot analysis revealed that the gene is expressed in NFS. Based on homologies of the glutamine-rich domain, the biological role of the pyk20 gene product as a transcription factor is assumed.

AND-34, a novel p130Cas-binding thymic stromal cell protein regulated by adhesion and inflammatory cytokines

We have characterized a novel cDNA whose steady state mRNA levels rise in the thymus 2 to 6 h following the induction of CD4+CD8+ thymocyte apoptosis by in vivo cross-linking of CD3 epsilon. This cDNA, AND-34-1, contains an open reading frame (ORF) encoding a protein with an amino-terminal Src homology 2 (SH2) domain and a carboxyl-terminal domain homologous to GDP-exchange factors (GEFs). Northern analysis demonstrates widespread expression of the AND-34 gene. Anti-CD3 epsilon treatment induces up-regulation of the AND-34 mRNA levels in total thymic RNA but not in RNA from purified thymocytes, suggesting that this transcript is derived from a thymic stromal cell population. IL-1 and TNF increase AND-34 transcript levels in thymic cortical reticular, thymic nurse, and fibroblast cell lines. In the thymic cortical reticular cell line, IL-1 and TNF induce a protein of the predicted 93-kDa size reactive with anti-AND-34 peptide antisera. Fifteen minutes of serum stimulation of vanadate-pretreated AND-34-1-transfected NIH3T3 fibroblasts induces tyrosine phosphorylation of AND-34 as well as coprecipitating 95-, 125-, and 130-kDa proteins. One of these tyrosine phosphorylated proteins is identified as p130Cas (Crk-associated substrate), a signaling molecule previously known to bind to a GDP-exchange factor (C3G) and inducibly associate with the focal adhesion complex. Consistent with such an association, AND-34 tyrosine phosphorylation is induced following adherence of trypsinized fibroblasts to fibronectin or poly-L -lysine-coated surfaces.

AND-34, a Novel p130Cas-Binding Thymic Stromal Cell Protein Regulated by Adhesion and Inflammatory Cytokines

We have characterized a novel cDNA whose steady state mRNA levels rise in the thymus 2 to 6 h following the induction of CD4+CD8+ thymocyte apoptosis by in vivo cross-linking of CD3ε. This cDNA, AND-34-1, contains an open reading frame (ORF) encoding a protein with an amino-terminal Src homology 2 (SH2) domain and a carboxyl-terminal domain homologous to GDP-exchange factors (GEFs). Northern analysis demonstrates widespread expression of the AND-34 gene. Anti-CD3ε treatment induces up-regulation of the AND-34 mRNA levels in total thymic RNA but not in RNA from purified thymocytes, suggesting that this transcript is derived from a thymic stromal cell population. IL-1 and TNF increase AND-34 transcript levels in thymic cortical reticular, thymic nurse, and fibroblast cell lines. In the thymic cortical reticular cell line, IL-1 and TNF induce a protein of the predicted 93-kDa size reactive with anti-AND-34 peptide antisera. Fifteen minutes of serum stimulation of vanadate-pretreated AND-34-1-transfected NIH3T3 fibroblasts induces tyrosine phosphorylation of AND-34 as well as coprecipitating 95-, 125-, and 130-kDa proteins. One of these tyrosine phosphorylated proteins is identified as p130Cas (Crk-associated substrate), a signaling molecule previously known to bind to a GDP-exchange factor (C3G) and inducibly associate with the focal adhesion complex. Consistent with such an association, AND-34 tyrosine phosphorylation is induced following adherence of trypsinized fibroblasts to fibronectin or poly-l-lysine-coated surfaces.

[Effect of regulation of kidney-yin and kidney-yang on hypothalamus-pituitary-adrenal-thymus axis in monosodium L-glutamate rats]

OBJECTIVE

To study the interrelationship between hypothalamus-pituitary-adrenal-thymus (HPAT) axis and Kidney-Yang and Kidney-Yin in arcuate nucleus destroyed rats.

METHODS

Monosodium glutamate (MSG) 4 mg/g body weight was given subcutaneously to neonatal rats at 2, 4, 6, 8 and 10th day after born to destroy the ARC, and Zuogui pill or Yougui pill (5 g/kg daily) was given respectively by gastrogavage when the model rats entered adulthood.

RESULTS

Immunohistochemical staining showed that in the model group the number of corticotropin-releasing hormone (CRH) positive neurons in hypothalamic paraventricular nucleus and anterior pituitary adrenotrophin (ACTH) positive secretory cells, which stained deeply, were more than those in the control group, the adrenal fasciculate zone disturbed with increased cells and obviously dilated sinusoid. The thymus atrophied with lymphocyte proliferation apparently lower, blood corticosterone, ACTH content and hypothalamic CRF level higher in the model than those in the control. Zuogui pill could improve above-mentioned pathophysiologic changes effectively but Yougui pill could not.

CONCLUSION

Process of pathophysiology of HPA axis hyperfunction accompanied cell-mediated immunodeficiency may belong to the category of Kidney-Yin Deficiency Syndrome.

[The role of nitric oxide on the functional change of interleukin-1 beta and interleukin-6 induced rat pancreatic islets of Langerhans]

OBJECTIVE

To observe the effects of interleukin (IL)-1 beta and IL-6 on nitric oxide (NO) production, islet cell DNA and insulin content, and MTT assay of rat pancreatic islets of Langerhans.

METHODS

Isolated pancreatic islet cells from SD rats were cultured in monolayer in vitro. Nitrite production, islet cell DNA and insulin content, and MTT assay in rat pancreatic islet cells incubated with IL-1 beta and IL-6, singly or in combination, were measured. The levels of these parameters of the cytokines in the absence and presence of N(G)-monomethyl-L-arginine (L-NMMA), an inhibitor of nitric oxide synthetase, were compared.

RESULTS

IL-1 beta induced a significant increase in nitrite production, a decrease of islet cell DNA and insulin content and reduction of cell activity (MTT, P < 0.001); these changes were blocked by L-NMMA (P < 0.001). IL-6 produced no significant change in those parameters (P > 0.05). The combination of IL-1 beta and IL-6 increased NO production, decreased islet cell DNA and insulin content and reduced cell activity (P < 0.001); the changes were similar to those with IL-1 beta alone (P > 0.05).

CONCLUSION

The cytotoxic effects of IL-1 beta on pancreatic islets might be mediated by NO. IL-6 may not be directly cytotoxic to pancreatic islets. It may be related with the fact that IL-6 does not induce NO production.

[Determination of triflumizole and its metabolite residues in vegetables by high performance liquid chromatography]

Triflumizole (TRI) and its metabolite [4-chloro-alpha,alpha,alpha-trifluoro-N-(1-amino-2-propoxythylidene)- O-toluidine] (MET) were extracted with methanol and reverse-extracted with dichloromethane. After evaporation to dryness, the residue in dichloromethane layer was dissolved in mobile phase for high performance liquid chromatographic determination with external standard method. The total residue content of TRI and MET (calculated as TRI) is reported.

Prior exposure to neurotrophins blocks inhibition of axonal regeneration by MAG and myelin via a cAMP-dependent mechanism

MAG is a potent inhibitor of axonal regeneration. Here, inhibition by MAG, and myelin in general, is blocked if neurons are exposed to neurotrophins before encountering the inhibitor; priming cerebellar neurons with BDNF or GDNF, but not NGF, or priming DRG neurons with any of these neurotrophins blocks inhibition by MAG/myelin. Dibutyryl cAMP also overcomes inhibition by MAG/myelin, and cAMP is elevated by neurotrophins. A PKA inhibitor present during priming abrogates the block of inhibition. Finally, if neurons are exposed to MAG/myelin and neurotrophins simultaneously, but with the Gi protein inhibitor, inhibition is blocked. We suggest that priming neurons with particular neurotrophins elevates cAMP and activates PKA, which blocks subsequent inhibition of regeneration and that priming is required because MAG/myelin activates a Gi protein, which blocks increases in cAMP. This is important for encouraging axons to regrow in vivo.

Structure of double-shelled rice dwarf virus

Rice dwarf virus (RDV), a member of the Reoviridae family, is a double-stranded RNA virus. Infection of rice plants with RDV reduces crop production significantly and can pose a major economic threat to Southeast Asia. A 25-A three-dimensional structure of the 700-A-diameter RDV capsid has been determined by 400-kV electron cryomicroscopy and computer reconstruction. The structure revealed two distinctive icosahedral shells: a T=13l outer icosahedral shell composed of 260 trimeric clusters of P8 (46 kDa) and an inner T=1 icosahedral shell of 60 dimers of P3 (114 kDa). Sequence and structural comparisons were made between the RDV outer shell trimer and the two crystal conformations (REF and HEX) of the VP7 trimer of bluetongue virus, an animal analog of RDV. The low-resolution structural match of the RDV outer shell trimer to the HEX conformation of VP7 trimer has led to the proposal that P8 consists of an upper domain of beta-sandwich motif and a lower domain of alpha helices. The less well fit REF conformation of VP7 to the RDV trimer may be due to the differences between VP7 and P8 in the sequence of the hinge region that connects the two domains. The additional mass density and the absence of a known signaling peptide on the surface of the RDV outer shell trimer may be responsible for the different interactions between plants and animal reoviruses.

[Somastostatin and growth hormone in preventing liver damage due to acute necrotizing pancreatitis]

OBJECTIVE

To study the role of somastostatin and growth hormone in preventing liver damage due to ANP.

METHODS

The roles of inflammatory mediators (Endotoxin, Amylase, TNF alpha) were investigated in ANP model by retrograde injection of 3.5% sodium taurocholate 2.5 ml/kg into the pancreatic duct, and TNF alpha mRNA in the liver after ANP was observed by reverse transcriptase-polymerase chain reaction. Besides, the effects of somastostain and growth hormone were also observed.

RESULTS

ANP caused remarkable elevation of those inflammatory mediators, being positively correlated with the development of pancreas and liver damage. Somastostain and growth hormone inhibited the inflammatory mediates and TNF alpha mRNA overexpression and reduced the damage to the pancreas and liver.

CONCLUSIONS

TNF alpha plays an important role in ANP progression, and somastostatin and growth hormone may prevent the development and progression of liver damage due to ANP.

[Clinical and experimental study on treatment of acute cerebral infarction with Acanthopanax Injection]

OBJECTIVE

To evaluate the effect of Radix Acanthopanacis Senticosi in treating acute cerebral infarction and its mechanism.

METHODS

Clinical study using single-blind, control trial, in which 60-80 ml of Acanthopanax Injection (AI) added to 500 ml of 0.9% normal saline was given by intravenous drip once a day for 14 days in the AI group(34 patients), while 500 ml of dextra-40 was given by the same way in the control group(26 patients). In experimental study, rabbit model of acute incomplete cerebral ischemia was made by ligation of bilateral common carotid artery. 10 ml of AI were given once daily intravenously for 7 days to the AI group and 10 ml of normal saline was given to the control group in the same way. Clinical effects (in clinical study) and effect of AI on cerebral oxygen free radicals (OFR), superoxide dismutase (SOD), and serum concentration of ACTH and cortisone were observed (in experimental study).

RESULTS

Clinical study showed that the total effective rate of AI group (86%) was higher than that of the control group (50%) while nervous functional deficit score was lower in AI group (9.96 +/- 4.66) than that in the control group (13.56 +/- 1.84) significantly. Experimental study showed that the cerebral level of OFR decreased while SOD increased and serum concentration of ACTH and cortisone decreased after treatment in AI group.

CONCLUSIONS

AI was effective in treating acute cerebral infarction, the mechanism is probably by ameliorating peroxidation in brain and improving hypothalamic-pituitary-adrenocortical axis function.

[Arthroscopy in diagnosis and treatment of tuberculous synovitis]

OBJECTIVE

To evaluate the role of arthroscopy in the diagnosis and treatment of early tuberculous synovitis.

METHOD

Eighteen patients with monoarticular synovitis who underwent arthroscopy and diagnosed as tuberculous synovitis because of arthroscopic findings and synovial biopsies from September 1986 to September 1996 were reviewed.

RESULT

Four out of 18 patients were diagnosed on the basis of clinical manifestations and laboratory results before operation, and proved pathologically after operation. The other 14 cases were definitely diagnosed by arthroscopy and pathological examination. With an average of 3 years and 4 months follow-up, the results of the treatment were excellent. Symptoms disappeared, and full joint functions restored in each case.

CONCLUSION

Arthroscopy is a useful method in the diagnosis and treatment of early tuberculous synovitis.

An ergonomic approach to public squatting-type toilet design

This paper reports a case study on public squatting-type toilet design, which was undertaken with a special emphasis on ergonomic considerations. A field survey on the use of public toilets in Taipei reveals that almost half of the subjects take a non-sitting posture while using the sitting-type public toilets and 86% of the subjects agreed that the squatting-type public toilets better satisfy sanitary requirements. An experiment was conducted to determine relevant anthropometric data for a redesign of squatting-type toilets. One of the variables studied was the effect of the footstep slope on squatting comfort. A total of 80 subjects as tested on four footstep slopes: 0 degrees, 15 degrees, 30 degrees and 45 degrees. Their heart rates were measured before and after the test, and their subjective evaluations of squatting comfort were also recorded. The 15 degrees slope was found to be preferred. These findings were then used in design development where mock-ups were presented to subjects for evaluation, then modifications were made and further tests conducted for verification. The result shows that the ergonomic approach is feasible recommended to be adopted in the process of product design of such facilities.

Co-purification of microsomal epoxide hydrolase with the warfarin-sensitive vitamin K1 oxide reductase of the vitamin K cycle

Vitamin K1 oxide reductase activity has been partially purified from rat liver microsomes. A three-step procedure produced a preparation in which warfarin-sensitive vitamin K1 oxide reductase activity was 118-fold enriched over the activity in intact rat liver microsomes. A major component of the multi-protein mixture was identified as a 50 kDa protein that strongly cross-reacts with antiserum prepared against homogeneous rat liver microsomal epoxide hydrolase. The reductase preparation also had a high level or epoxide hydrolase activity against two xenobiotic epoxide substrates. The K(m) values for hydrolysis by the reductase preparation were similar to those for homogeneous microsomal epoxide hydrolase itself, and the specific hydrolase activities of the reductase preparation were 25-35% of the specific activities measured for the homogeneous hydrolase preparation. Antibodies prepared against homogeneous microsomal epoxide hydrolase inhibited up to 80% of reductase activity of the reductase preparation. Homogeneous microsomal epoxide hydrolase had no vitamin K1 oxide reductase activity. This evidence suggests that microsomal epoxide hydrolase, or a protein that is very similar to it, is a major functional component of a multi-protein complex that is responsible for vitamin K1 oxide reduction in rat liver microsomes.

[Clinical and experimental research of Epimedium brevicornum in relieving neuroendocrino-immunological effect inhibited by exogenous glucocorticoid]

OBJECTIVE

To study protective effect of Epimedium brevicornum (EB) on hypothalamus-pituitary-adrenal-thymus (HPAT) axis inhibited by exogenous glucocorticoid.

METHODS

In clinical research, variation of cortisol, adrenocorticotrophin (ACTH), lymphocyte proliferative reaction were observed before and after medication in 65 patients took prednisone, and were randomly divided into Fufang prednisone group (mixture of prednisone and EB) and prednisone group. An experimental model of HPAT axis inhibited by corticosterone (CORT) was established to observe the effect of EB on relevant indices of HPAT axis.

RESULTS

The level of ACTH and CORT in plasma decreased and lymphocyte proliferative reaction reduced in patients (P < 0.05). In experimental study, monoaminic transmitters activated in hypothalamus; weight of pituitary, adrenal and thymus decreased; number of CRH positive neurons in hypothalamic paraventricular nucleus, CRH positive neurofibrilin median eminence and anterior pituitary ACTH positive secretory cells decreased; adrenal fasciculate zone and thymus cortex atrophies; NK cell cytotoxicity and the level of IL-2 and gamma-IFN which were produced by lymphocytes reduced in CORT-rats (P < 0.05). There were significant difference between Fufang prednisone group (clinical research) or EB group (experimental research) and CORT control groups, P < 0.05.

CONCLUSION

EB could relieve neuroendocrino-immunological effect inhibited by exogenous glucocorticoid.

Mechanism-based inactivation of a yeast methylamine oxidase mutant: implications for the functional role of the consensus sequence surrounding topaquinone

The copper-containing yeast methylamine oxidase E406N mutant has an altered consensus sequence surrounding the topaquinone cofactor (residue 405). The mutation has no effect on the final yield of the active-site topaquinone cofactor during biogenesis but causes the enzyme to be inactivated by substrate methylamine [Cai, D., and Klinman, J. P. (1994) Biochemistry 33, 7674-7653]. In this study we show that the inactivation leads to the formation of a covalent adduct, which has a UV/vis spectrum very similar to that of a product Schiff base, an intermediate of topaquinone-catalyzed amine oxidation reactions. The kinetic isotope effects on the second-order rate constant for the inactivation and catalytic turnover are identical, indicating that the two processes share a common intermediate that follows C_H bond cleavage. Resonance Raman spectroscopy provides direct evidence for the accumulation of a neutral product Schiff base species. Removal of excess methylamine leads to recovery of both activity and the native absorption spectrum for E406N, indicating that the cofactor in the inactivated enzyme is chemically competent for hydrolysis. The rate of the reactivation is slow, however; the shortest half-life of the inhibited E406N at 25 degrees C is 5.9 min at pH 6.15. pH effect experiments show that the inactivation and reactivation steps are controlled by a single ionizable group with a pKa of 6.9-7.1; under basic conditions, when this residue is deprotonated, the inactivation is the fastest and the half-life of the inhibited enzyme is the longest. On the basis of the available crystal structures of copper amine oxidases, we propose that a histidine residue in the dimer interface is responsible for the observed ionization. In the wild-type enzyme this histidine is kept protonated by virtue of Glu at position 406. Unlike methylamine, the larger substrates ethylamine and benzylamine give normal turnover with E406N. Disruption of structure at the subunit interface in E406N may allow a rotation of the relatively small topa-product Schiff base complex (formed from methylamine) away from the active-site base to a conformation that is incompetent toward hydrolysis.

Effect of metal on 2,4,5-trihydroxyphenylalanine (topa) quinone biogenesis in the Hansenula polymorpha copper amine oxidase

Previous studies of wild-type and mutant forms of a recombinant copper amine oxidase from Hansenula polymorpha, expressed in Saccharomyces cerevisiae, have indicated a self-processing mechanism for 2,4,5-trihydroxyphenylalanine (topa) quinone biogenesis involving the active site copper (Cai, D., and Klinman, J. P. (1994) J. Biol. Chem. 269, 32039-32042). In contrast to prokaryotic copper amine oxidases, however, it has not been possible to initiate topa quinone formation by the addition of exogenous copper to precursor H. polymorpha amine oxidase lacking copper. Metal analysis of copper-depleted wild-type enzyme reveals 0.2-0.3 mol copper, together with 0.6 mol zinc. Despite changes in the zinc and copper levels in growth media, the level of zinc in purified enzyme remains fairly constant. Further, we have been unable to displace protein-bound zinc by exogenously added copper. The H. polymorpha amine oxidase gene was subsequently expressed in Escherichia coli and found to be almost completely free of copper and zinc. In vitro reconstitution of this apoprotein confirms that zinc binds to H. polymorpha amine oxidase and prevents reconstitution with copper. By contrast, addition of copper first to apoprotein leads to formation of topa quinone and stable activity in the presence of added zinc. These findings indicate efficient binding of either zinc or copper to a site that undergoes little or no exchange. The data confirm that topa quinone biogenesis in the H. polymorpha system is catalyzed by copper and occurs in the absence of added factors. We conclude that the mechanisms of cofactor biogenesis in pro- and eukaryotic systems are likely to be similar or identical. The results described herein imply different pathways for the in vivo assembly of heterologously expressed amine oxidases in S. cerevisiae and E. coli.

Spatiotemporal receptive field organization in the lateral geniculate nucleus of cats and kittens

We have studied the spatiotemporal receptive-field organization of 144 neurons recorded from the dorsal lateral geniculate nucleus (dLGN) of adult cats and kittens at 4 and 8 wk postnatal. Receptive-field profiles were obtained with the use of a reverse correlation technique, in which we compute the cross-correlation between the action potential train of a neuron and a randomized sequence of long bright and dark bar stimuli that are flashed throughout the receptive field. Spatiotemporal receptive-field profiles of LGN neurons generally exhibit a biphasic temporal response, as well as the classical center-surround spatial organization. For nonlagged cells, the first temporal phase of the response dominates, whereas for lagged neurons, the second temporal phase of the response is typically the largest. This temporal phase difference between lagged and nonlagged cells accounts for their divergent behavior in response to flashed stimuli. Most LGN cells exhibit some degree of space-time inseparability, which means that the receptive field cannot simply be viewed as the product of a spatial waveform and a temporal waveform. In these cases, the response of the surround is typically delayed relative to that of the center, and there is some blending of center and surround during the time course of the response. We demonstrate that a simple extension of the traditional difference-of-Gaussians (DOG) model, in which the surround response is delayed relative to that of the center, accounts nicely for these findings. With regard to development, our analysis shows that spatial and temporal aspects of receptive field structure mature with markedly different time courses. After 4 wk postnatal, there is little change in the spatial organization of LGN receptive fields, with the exception of a weak, but significant, trend for the surround to become smaller and stronger with age. In contrast, there are substantial changes in temporal receptive-field structure after 4 wk postnatal. From 4 to 8 wk postnatal, the shape of the temporal response profile changes, becoming more biphasic, but the latency and duration of the response remain unchanged. From 8 wk postnatal to adulthood, the shape of the temporal profile remains approximately constant, but there is a dramatic decline in both the latency and duration of the response. Comparison of our results with recent data from cortical (area 17) simple cells reveals that the temporal development of LGN cells accounts for a substantial portion of the temporal maturation of simple cells.

Crystallographic Study of Yeast Copper Amine Oxidase

The copper-containing amine oxidase from the yeast Hansenula polymorpha (YAO) has been crystallized and partially solved by molecular replacement. It catalyzes the oxidative deamination of primary amines by molecular oxygen to the corresponding aldehydes, ammonia and hydrogen peroxide. It contains a covalently bound redox cofactor, topa quinone, generated by post-translational modification of a single tyrosine side chain. The crystals of YAO are orthorhombic, with space-group symmetry P2(1)2(1)2(1) and unit-cell dimensions a = 138.8, b = 148.2, c = 234.0 A and diffract X-rays beyond 2.0 A resolution. Solution by molecular replacement using the E. coli amine oxidase structure [Parsons, Convery, Wilmot, Yadav, Blakeley, Corner, Philips, McPherson & Knowles (1995). Structure, 3, 1171-1184] as a search model reveals that there are three dimers in the asymmetric unit in a trigonal arrangement having 32 point-group symmetry. The solution agrees well with the self-rotation function of YAO. The non-crystallographic threefold axis lies parallel to a crystallographic twofold screw axis and each dimer has twofold symmetry. Phases from the refined model based on the molecular-replacement solution were used to solve one heavy-atom derivative. Model building from the unbiased isomorphous replacement phases is in progress.

Inhibition of recombinant Ca2+ channels by benzothiazepines and phenylalkylamines: class-specific pharmacology and underlying molecular determinants

To understand the molecular basis of state-dependent pharmacological blockade of voltage-gated Ca2+ channels, we systematically characterized phenylalkylamine and benzothiazepine inhibition of three molecular classes of Ca2+ channels (alpha1C, alpha1A, and alpha1E) expressed from cDNA clones transfected into HEK 293 cells. State-dependent blockade figures importantly in the therapeutically desirable property of use-dependent drug action. Verapamil (a phenylalkylamine) and diltiazem (a benzothiazepine) were imperfectly selective, so differences in the state dependence of inhibition could be compared among the various channels. We found only quantitative differences in pharmacological profile of verapamil: half-maximal inhibitory concentrations spanned a 2-fold range (70 microM for alpha1A, 100 microM for alpha1E, and 110 microM for alpha1C), and inhibition was state dependent in all channels. In contrast, diltiazem produced only state-dependent block of alpha1C channels; alpha1A and alpha1E channels demonstrated state-independent block despite similar half-maximal inhibitory concentrations (60 microM for alpha1C, 220 microM for alpha1E, and 270 microM for alpha1A). To explore the molecular basis for the sharp distinction in state-dependent inhibition by diltiazem, we constructed chimeric channels from alpha1C and alpha1A and localized the structural determinants for state dependence to repeats III and IV of alpha1C, which have been found to contain the structures required for benzothiazepine binding. We then constructed a mutant alpha1C construct by changing three amino acids in IVS6 (Y14901, A1494S, 11497M) that have been implicated as key coordinating sites for avid benzothiazepine binding. Although these mutations increased the half-maximal inhibitory concentration of diltiazem inhibition by approximately 10-fold, the state-dependent nature of inhibition was spared. This result points to the existence of physically distinct elements controlling drug binding and access to the binding site, thereby favoring a "guarded-receptor" rather than a "modulated-receptor" mechanism of drug inhibition.