Gating of inward rectifier K+ channels by proton-mediated interactions of N- and C-terminal domains

Ion channels play an important role in cellular functions, and specific cellular activity can be produced by gating them. One important gating mechanism is produced by intra- or extracellular ligands. Although the ligand-mediated channel gating is an important cellular process, the relationship between ligand binding and channel gating is not well understood. It is possible that ligands are involved in the interactions of different protein domains of the channel leading to opening or closing. To test this hypothesis, we studied the gating of Kir2.3 (HIR) by intracellular protons. Our results showed that hypercapnia or intracellular acidification strongly inhibited these channels. This effect relied on both the N and C termini. The CO(2)/pH sensitivities were abolished or compromised when one of the intracellular termini was replaced. Using purified N- and C-terminal peptides, we found that the N and C termini bound to each other in vitro. Although their binding was weak at pH 7.4, stronger binding was seen at pH 6.6. Two short sequences in the N and C termini were found to be critical for the N/C-terminal interaction. Interestingly, there was no titratable residue in these motifs. To identify the potential protonation sites, we systematically mutated most histidine residues in the intracellular N and C termini. We found that mutations of several histidine residues in the C but not the N terminus had a major effect on channel sensitivities to CO(2) and pH(i). These results suggest that at acidic pH, protons appear to interact with the C-terminal histidine residues and present the C terminus to the N terminus. Consequentially, these two intracellular termini bound to each other through two short motifs and closed the channel. Thus, a novel mechanism for K(+) channel gating is demonstrated, which involves the N- and C-terminal interaction with protons as the mediator.

Mechanisms of discordant alternans and induction of reentry in simulated cardiac tissue

BACKGROUND

T-wave alternans, which is associated with the genesis of cardiac fibrillation, has recently been related to discordant action potential duration (APD) alternans. However, the cellular electrophysiological mechanisms responsible for discordant alternans are poorly understood.

METHODS AND RESULTS

We simulated a 2D sheet of cardiac tissue using phase 1 of the Luo-Rudy cardiac action potential model. A steep (slope >1) APD restitution curve promoted concordant APD alternans and T-wave alternans without QRS alternans. When pacing was from a single site, discordant APD alternans occurred only when the pacing rate was fast enough to engage conduction velocity (CV) restitution, producing both QRS and T-wave alternans. Tissue heterogeneity was not required for this effect. Discordant alternans markedly increases dispersion of refractoriness and increases the ability of a premature stimulus to cause localized wavebreak and induce reentry. In the absence of steep APD restitution and of CV restitution, sustained discordant alternans did not occur, but reentry could be induced if there was marked electrophysiological heterogeneity. Both discordant APD alternans and preexisting APD heterogeneity facilitate reentry by causing the waveback to propagate slowly.

CONCLUSION

Discordant alternans arises dynamically from APD and CV restitution properties and markedly increases dispersion of refractoriness. Preexisting and dynamically induced (via restitution) dispersion of refractoriness independently increase vulnerability to reentrant arrhythmias. Reduction of dynamically induced dispersion by appropriate alteration of electrical restitution has promise as an antiarrhythmic strategy.

Mechanisms of ventricular fibrillation induction by 60-Hz alternating current in isolated swine right ventricle

BACKGROUND

The mechanisms by which 60-Hz alternating current (AC) can induce ventricular fibrillation (VF) are unknown.

METHODS AND RESULTS

We studied 7 isolated perfused swine right ventricles in vitro. The action potential duration restitution curve was determined. Optical mapping techniques were used to determine the patterns of activation on the epicardium during 5-second 60-Hz AC stimulation (10 to 999 microA). AC captured the right ventricles at 100+/-65 microA, which is significantly lower than the direct current pacing threshold (0.77+/-0.45 mA, P:<0.05). AC induced ventricular tachycardia or VF at 477+/-266 microA, when the stimulated responses to AC had (1) short activation CLs (128+/-14 ms), (2) short diastolic intervals (16+/-9 ms), and (3) short diastolic intervals associated with a steep action potential duration restitution curve. Optical mapping studies showed that during rapid ventricular stimulation by AC, a wave front might encounter the refractory tail of an earlier wave front, resulting in the formation of a wave break and VF. Computer simulations reproduced these results.

CONCLUSIONS

AC at strengths less than the regular pacing threshold can capture the ventricle at fast rates. Accidental AC leak to the ventricles could precipitate VF and sudden death if AC results in a fast ventricular rate coupled with a steep restitution curve and a nonuniform recovery of excitability of the myocardium.

[Clinical results of transmyocardial laser revascularization for 77 patients with coronary artery disease]

OBJECTIVE

To analyses the clinical results of transmyocardial laser revascularization (TMLR) for 77 patients with coronary artery diseases (CAD).

METHODS

The mean age of the patients was (65 +/- 7) years. Previous medical record included CABG (6 patients), PTCA (9), AMI (66.2%), hypertension (70.1%), and diabetes mellitus (45.5%). TMLR was performed on the beating heart via a left anterolateral thoracotomy at the fifth intercostal space. Transesophageal echocardiography showed transmyocardial penetration of 23 +/- 6 channels.

RESULTS

The hospital mortality was 3.8%, and postoperative complications were AMI (3.8%), left ventricular failure (2.6%), PVC (5.2%). After operation, the mean CCS angina class was improved from the baseline 3.5 +/- 0.7 to 2.1 +/- 0.3 at 3 months, 1.7 +/- 0.3 at 6 months, 1.7 +/- 0.3 at 12 months and 1.8 +/- 0.4 at 24 months. One patient died of AMI and two died not due to cardiac events during a follow-up of 3 to approximately 24 months. Echocardiography showed that the average of left ventricular ejection fractions was improved significantly at 6 months after operation compared with the preoperative value (P = 0.0457). (201)TI-SPECT showed a remarkable improvement in reversible ischemia in 70% patients followed up. Metabolic stress test for 20 patients followed up patients demonstrated an average increase in exercise tolerance from 7.1 +/- 3.2 min at the baseline to 9.6 +/- 1.3 min at 12 months (P = 0.021). Similarly the METs increased from 4.3 +/- 2.1 at the baseline to 5.4 +/- 2.0 at 12 months.

CONCLUSIONS

TMLR is a safe and effective procedure for the treatment of end stage coronary artery diseases not amenable to PTCA or CABG. The effect of TMLR is associated with indication, correct evaluation of myocardial ischemia, and management for postoperative complications.

Ascorbate-dependent protection of human erythrocytes against oxidant stress generated by extracellular diazobenzene sulfonate

Diazobenzene sulfonic acid (DABS) has been used to label thiols and amino groups on cell-surface proteins. However, we found that in addition to inhibiting an ascorbate-dependent trans-plasma membrane oxidoreductase in human erythrocytes, it also depleted alpha-tocopherol severely in the cell membrane. When erythrocytes were loaded with ascorbate, DABS-dependent loss of alpha-tocopherol was decreased, despite little change in intracellular ascorbate content. Sparing of alpha-tocopherol also was seen in erythrocyte ghosts resealed to contain ascorbate, although this was accompanied by loss of intravesicular ascorbate, probably due to the inability of ghosts to recycle ascorbate. A transmembrane transfer of electrons from ascorbate was confirmed by electron paramagnetic resonance spectroscopy, in which extracellular DABS was found to generate the ascorbate free radical within cells. When the membrane content of alpha-tocopherol was decreased to 20% of the initial value by DABS treatment, lipid peroxidation ensued, manifest by generation of F(2)-isoprostanes in the cell membranes. Intracellular ascorbate also strongly protected against F(2)-isoprostane formation. These results show that DABS causes an oxidant stress at the membrane surface that is transmitted within the cell, in part by an alpha-tocopherol-dependent mechanism, and that ascorbate recycling of alpha-tocopherol can protect against loss of alpha-tocopherol and the ensuing lipid peroxidation.

Origins of spiral wave meander and breakup in a two-dimensional cardiac tissue model

We studied the stability of spiral waves in homogeneous two-dimensional cardiac tissue using phase I of the Luo-Rudy ventricular action potential model. By changing the conductance and the relaxation time constants of the ion channels, various spiral wave phenotypes, including stable, quasiperiodically meandering, chaotically meandering, and breakup were observed. Stable and quasiperiodically meandering spiral waves occurred when the slope of action potential duration (APD) restitution was < 1 over all diastolic intervals visited during reentry; chaotic meander and spiral wave breakup occurred when the slope of APD restitution exceeded 1. Curvature of the wave changes both conduction velocity and APD, and their restitution properties, thereby modulating local stability in a spiral wave, resulting in distinct spiral wave phenotypes. In the LRI model, quasiperiodic meander is most sensitive to the Na+ current, whereas chaotic meander and breakup are more dependent on the Ca2+ and K+ currents.

Scroll wave dynamics in a three-dimensional cardiac tissue model: roles of restitution, thickness, and fiber rotation

Scroll wave (vortex) breakup is hypothesized to underlie ventricular fibrillation, the leading cause of sudden cardiac death. We simulated scroll wave behaviors in a three-dimensional cardiac tissue model, using phase I of the Luo-Rudy (LR1) action potential model. The effects of action potential duration (APD) restitution, tissue thickness, filament twist, and fiber rotation were studied. We found that APD restitution is the major determinant of scroll wave behavior and that instabilities arising from APD restitution are the main determinants of scroll wave breakup in this cardiac model. We did not see a "thickness-induced instability" in the LR1 model, but a minimum thickness is required for scroll breakup in the presence of fiber rotation. The major effect of fiber rotation is to maintain twist in a scroll wave, promoting filament bending and thus scroll breakup. In addition, fiber rotation induces curvature in the scroll wave, which weakens conduction and further facilitates wave break.

Preventing ventricular fibrillation by flattening cardiac restitution

Ventricular fibrillation is the leading cause of sudden cardiac death. In fibrillation, fragmented electrical waves meander erratically through the heart muscle, creating disordered and ineffective contraction. Theoretical and computer studies, as well as recent experimental evidence, have suggested that fibrillation is created and sustained by the property of restitution of the cardiac action potential duration (that is, its dependence on the previous diastolic interval). The restitution hypothesis states that steeply sloped restitution curves create unstable wave propagation that results in wave break, the event that is necessary for fibrillation. Here we present experimental evidence supporting this idea. In particular, we identify the action of the drug bretylium as a prototype for the future development of effective restitution-based antifibrillatory agents. We show that bretylium acts in accord with the restitution hypothesis: by flattening restitution curves, it prevents wave break and thus prevents fibrillation. It even converts existing fibrillation, either to a periodic state (ventricular tachycardia, which is much more easily controlled) or to quiescent healthy tissue.

Metabolic effects of insulin and insulin-like growth factor-I in endotoxemic rats during total parenteral nutrition feeding

The effects of insulin and insulin-like growth factor-I (IGF-I) on protein, energy, and glucose metabolism were examined in endotoxemic rats receiving total parenteral nutrition (TPN) for 3 days. The endotoxemic model was induced by constant infusion of lipopolysaccharide (1 mg/kg x d) for 3 days. The TPN regimen provided 200 kcal/kg x d and 1.5 g protein/kg x d. The dosage of insulin (5 mU/kg x h) and IGF-I (20 microg/kg x h), either alone or in combination, was chosen to maintain normal levels of leucine and glucose in plasma during feeding. One normal control and 4 endotoxemic groups with different treatments (saline, IGF-I, insulin, or IGF-I and insulin) were included. The effects of endotoxin were compared between the group receiving endotoxin alone and normal controls, and the effects of insulin and IGF-I were compared within the endotoxemic groups. The results show that endotoxin significantly increased the mortality and induced a hypermetabolic state, and nutrition alone could not overcome the catabolism induced by endotoxin. However, administration of insulin and IGF-I enhanced protein preservation in muscle tissue in endotoxemic rats during TPN. This effect was greater for insulin either alone or in combination with IGF-I. Insulin also significantly reduced the mortality. There were no additive effects of these two anabolic hormones on any measured parameter in these experimental conditions.

Modulation of kir4.1 and kir5.1 by hypercapnia and intracellular acidosis

CO2 chemoreception may be mediated by the modulation of certain ion channels in neurons. Kir4.1 and Kir5.1, two members of the inward rectifier K+ channel family, are expressed in several brain regions including the brainstem. To test the hypothesis that Kir4.1 and Kir5. 1 are modulated by CO2 and pH, we carried out experiments by expressing Kir4.1 and coexpressing Kir4.1 with Kir5.1 (Kir4.1-Kir5. 1) in Xenopus oocytes. K+ currents were then studied using two-electrode voltage clamp and excised patches. Exposure of the oocytes to CO2 (5, 10 and 15 %) produced a concentration-dependent inhibition of the whole-cell K+ currents. This inhibition was fast and reversible. Exposure to 15 % CO2 suppressed Kir4.1 currents by approximately 20 % and Kir4.1-Kir5.1 currents by approximately 60 %. The effect of CO2 was likely to be mediated by intracellular acidification, because selective intracellular, but not extracellular, acidification to the measured hypercapnic pH levels lowered the currents as effectively as hypercapnia. In excised inside-out patches, exposure of the cytosolic side of membranes to solutions with various pH levels brought about a dose-dependent inhibition of the macroscopic K+ currents. The pK value (-log of dissociation constant) for the inhibition was 6.03 in the Kir4.1 channels, while it was 7.45 in Kir4.1-Kir5.1 channels, an increase in pH sensitivity of 1.4 pH units. Hypercapnia without changing pH did not inhibit the Kir4.1 and Kir4.1-Kir5.1 currents, suggesting that these channels are inhibited by protons rather than molecular CO2. A lysine residue in the N terminus of Kir4.1 is critical. Mutation of this lysine at position 67 to methionine (K67M) completely eliminated the CO2 sensitivity of both the homomeric Kir4. 1 and heteromeric Kir4.1-Kir5.1. These results therefore indicate that the Kir4.1 channel is inhibited during hypercapnia by a decrease in intracellular pH, and the coexpression of Kir4.1 with Kir5.1 greatly enhances channel sensitivity to CO2/pH and may enable cells to detect both increases and decreases in PCO2 and intracellular pH at physiological levels.

CO(2) inhibits specific inward rectifier K(+) channels by decreases in intra- and extracellular pH

Hypercapnia has been shown to affect cellular excitability by modulating K(+) channels. To understand the mechanisms for this modulation, four cloned K(+) channels were studied by expressing them in Xenopus oocytes. Exposures of the oocytes to CO(2) for 4-6 min produced reversible and concentration-dependent inhibitions of Kir1.1 and Kir2.3 currents, but had no effect on Kir2.1 and Kir6.1 currents. Intra- and extracellular pH (pH(i), pH(o)) dropped during CO(2) exposures. The inhibition of Kir2.3 currents was mediated by reductions in both intra- and extracellular pH, whereas the suppression of Kir1.1 resulted from intracellular acidification. In cell-free excised inside-out patches with cytosolic-soluble factors washed out, a decrease in pH(i) produced a fast and reversible inhibition of macroscopic Kir2.3 currents. The degree of this inhibition was similar to that produced by hypercapnia when compared at the same pH(i) level. Exposure of cytosolic surface of patch membranes to a perfusate bubbled with 15% CO(2) without changing pH failed to inhibit the Kir2.3 currents. These results therefore indicate that (1) hypercapnia inhibits specific K(+) channels, (2) these inhibitions are caused by intra- and extracellular protons rather than molecular CO(2), and (3) these effects are independent of cytosol-soluble factors.

Involvement of histidine residues in proton sensing of ROMK1 channel

ROMK channels are inhibited by intracellular acidification. This pH sensitivity is related to several amino acid residues in the channel proteins such as Lys-61, Thr-51, and His-206 (in ROMK2). Unlike all other amino acids, histidine is titratable at pH 6-7 carrying a positive charge below pH 6. To test the hypothesis that certain histidine residues are engaged in CO(2) and pH sensing of ROMK1, we performed experiments by systematic mutations of all histidine residues in the channel using the site-directed mutagenesis. There are two histidine residues in the N terminus. Mutations of His-23, His-31, or both together did not affect channel sensitivity to CO(2). Six histidine residues are located in the C terminus. His-225, His-274, His-342, and His-354 were critical in CO(2) and pH sensing. Mutation of either of them reduced CO(2) and pH sensitivities by 20-50% and approximately 0.2 pH units, respectively. Simultaneous mutations of all of them eliminated the CO(2) sensitivity and caused this mutant channel to respond to only extremely acidic pH. Similar mutations of His-280 had no effect. The role of His-270 in CO(2) and pH sensing is unclear, because substitutions of this residue with either a neutral, negative, or positive amino acid did not produce any functional channel. These results therefore indicate that histidine residues contribute to the sensitivity of the ROMK1 channel to hypercapnia and intracellular acidosis.

Matching host muscle and donor myoblasts for myosin heavy chain improves myoblast transfer therapy

Intensive efforts have been made to develop an effective therapy for Duchenne muscular dystrophy (DMD). Although myoblast transplantation has been found capable of transiently delivering dystrophin and improving the strength of the injected dystrophic muscle, this approach has been hindered by the immune rejection problems as well as the poor survival and limited spread of the injected cells. In the present study, we have investigated whether the careful selection of donor myoblasts and host muscle for the myosin heavy chain expression (MyHCs) plays a role in the success of myoblast transfer. Highly purified normal myoblasts derived from the m. soleus and m. gastrocnemius white of normal mice were transplanted into the m. soleus (containing 70% of type I fibers) and gastrocnemius white (100% of type II fibers) of dystrophin deficient mdx mice. At several time-points after injection (10, 20 and 30 days), the number of dystrophin-positive fibers was monitored and compared among the different groups. A significantly higher number and better persistence of dystrophin-positive myofibers were observed when the injected muscle and donor myoblasts expressed a similar MyHC in comparison with myoblast transfer between host muscle and donor myoblasts that were not matched for MyHC. These results suggest that careful matching between the injected myoblasts and injected muscle for the MyHC expression can improve the efficiency of myoblast-mediated gene transfer to skeletal muscle. Gene Therapy (2000) 7, 428-437.

From local to global spatiotemporal chaos in a cardiac tissue model

Two kinds of chaos can occur in cardiac tissue, chaotic meander of a single intact spiral wave and chaotic spiral wave breakup. We studied these behaviors in a model of two-dimensional cardiac tissue based on the Luo-Rudy I action potential model. In the chaotic meander regime, chaos is spatially localized to the core of the spiral wave. When persistent spiral wave breakup occurs, there is a transition from local to global spatiotemporal chaos.

In vivo production of type 1 cytokines in healthy sickle cell disease patients

Interleukins (IL)-1, 2, 12, and interferon (IFN)-gamma, along with soluble IL-2 receptor (sIL-2R) were measured from sera obtained from healthy sickle cell disease (SCD) patients and comparable healthy control subjects. The cytokines were assessed by enzyme-linked immunosorbent assay (ELISA) in 60 SCD patients and 58 controls. No significant detectable levels of IL-1 or IL-12 were found in the sera of either group of patients. Significantly elevated levels of IFN-gamma were measured in 20 (33%) of 60 SCD patients and 21 (36%) of 58 controls. A large subset of 18 (41%) of 43 healthy controls and a smaller subset of 12 (21%) of 58 SCD demonstrated detectable levels of IL-2. The sIL-2R levels of the SCD group (4465 +/- 552 pg/mL) were significantly higher (P < .0001) than that of controls (3473 +/- 411 pg/mL). The results revealed comparable circulating levels of all type 1 cytokines in both healthy SCD and normal control subjects, with the exception of in vivo sIL-2R production. Elevated serum levels of both IL-6 and tumor necrosis factor (TNF)-alpha have been reported previously in a significant percentage of SCD steady-state subjects. These two cytokines are known to increase sIL-2R expression and may help explain the difference between the patient populations. Immune activation markers such as sIL-2R are produced by cells that mediate host responses to infection or inflammatory stimuli. The implication of higher levels of sIL-2R in SCD is not clear, but chronic parvovirus B19 infection, chronic polyclonal activation of B cells or defective regulation of antibodies are possible explanations for the elevated levels in SCD.

Humanization of Immu31, an alpha-fetoprotein-specific antibody

Immu31 is a murine monoclonal antibody (Ab) specific for alpha-fetoprotein (AFP), a tumor-associated marker. The excellent tumor targeting ability of Immu31 has led to the development of a Immu31-based radioimmunodiagnostic agent, AFP-Scan, for hepatocellular carcinoma and other AFP-producing tumors. To enhance the capability of Immu31-based immunoconjugates being used in diagnostic and therapeutic procedures in humans, a humanized version of Immu31 (hImmu31) was constructed by grafting the complementarity determining regions (CDRs) of murine variable domains for the heavy (VH) and kappa (Vkappa) chain to the respective human VH and Vkappa framework regions (FRs). The cDNA encoding the VH and Vkappa of Immu31 was cloned by reverse transcription-PCR from hybridoma cells, and a chimeric Immu31 (cImmu31) composed of murine V and human C domains was constructed. Competitive ELISA assays showed identical AFP binding activity between the chimeric and murine Abs, confirming the authenticity of the cloned V genes. Based on sequence homology, the EU FR1, FR2, and FR3 and the NEWM FR4 were selected as the scaffold for grafting VH CDRs and REI FRs for Vkappa CDRs of Immu31. The amino acid residues in murine FRs that are considered to be in contact with the CDRs of the Ab were maintained in the humanized version. hImmu31, thus constructed and expressed, showed comparable immunoreactivity in a competitive binding ELISA assay to that of murine Immu31 and cImmu31. High-level production was achieved by expressing hImmu31 in a dhfr-based amplifiable system, and the productivity has exceeded 100 mg/liter in terminal cultures.

Generation and monitoring of cell lines producing humanized antibodies

Antibody humanization has eliminated or reduced the human antimouse antibody response associated with the administration of murine antibodies. We have successfully humanized three different antibodies: (a) hMN-3 (granulocyte targeting); (b) hMu-9 (colorectal cancer targeting); and (c) hWI2 (anti-idiotype to the anti-carcinoembryonic antigen antibody MN-14). All humanized antibodies demonstrated immunoreactivities comparable to their parent counterparts. Previously, we reported the generation of high productivity cell lines for hMN-14 and hLL2 using the amplifiable vector pdHL2. Through amplification, selection, and cloning procedures, cell lines capable of large scale production were established, and further enhancement of production was achieved by a fed-perfusion bioreactor process. Using a similar and improved approach, we have enhanced the production of the above-mentioned humanized antibodies by gene amplification induced by a stepwise increase in the concentration of methotrexate in the culture media. A reliable IgG determination method is essential to monitor amplification, especially at the final cloning stage, for the selection of the subclones with the highest productivity. We found that measurement of humanized IgG concentration in culture media supplemented with more than 1 microM methotrexate by a standard ELISA assay could be unreliable and misleading. Whereas the determination of antibody by adsorption/elution on protein A from a 100-ml culture is accurate and reproducible, the method is time-consuming, tedious, and labor intensive. We have recently developed a Western blot assay that enables us to monitor the productivity of the cultures. The assay is simple and sensitive, and it makes simultaneous determinations of relative antibody production from individual clones at the 96-well stage feasible. With this method, amplification, cloning, and adaptation to serum-free conditions of multiple cell lines can be monitored in an efficient manner.

The effects of domain deletion, glycosylation, and long IgG3 hinge on the biodistribution and serum stability properties of a humanized IgG1 immunoglobulin, hLL2, and its fragments

Antibody (Ab) fragments are preferred agents for imaging applications because of their rapid clearance from the blood, thereby providing high tumor:blood ratios within a few hours. Several preclinical studies have also suggested that Ab fragments might be preferred for therapeutic applications over an intact IgG. The purpose of this project was to develop engineered Ab fragments using a humanized anti-carcinoembryonic antigen and anti-CD22 Ab as the parent. Three types of variants were prepared: a deltaCH2 (deletion mutant missing the CH2), a gamma3 F(ab')2 containing the human IgG3 hinge, and three glycosylated variants. The gamma3 F(ab')2 and glycosylated variants were developed because of the potential for site-specific linkage to the Ab in its divalent or monovalent fragment. The gamma3 F(ab')2 variant contains 10 cysteine residues that could be used for direct coupling using thiol chemistry, whereas the glycosylated variants have N-linked glycosylation sites engineered in the CH1 domain (two variants) as well as the VK domain (one variant). All of these variants were successfully prepared and shown to react with the target antigen. All Abs could be purified to a single peak by size-exclusion HPLC, but the deltaCH2 variant showed two distinct peaks, which were believed to be both the divalent and monovalent forms of this fragment. The two CH1 glycosylated variants showed differences in the extent of glycosylation. Modeling studies suggest that one variant would be better suited for site-specific coupling than the other because the carbohydrate chain is extended further away from the antigen-binding site. The Abs were radioiodinated to determine their pharmacokinetic behavior in mice. All of the humanized Ab divalent fragments cleared nearly 20 times faster from the blood than the murine parent F(ab')2 over a 24-h period. The glycosylated fragments showed some added stability compared to the other fragments over 4 h, but by 24 h, they had cleared to the same extent. Size-exclusion high-performance liquid chromatography of blood samples indicated that the humanized Ab fragments were quickly degraded in the blood. Thus, there is an inherent instability of the divalent fragments from these humanized IgG1 constructs that may affect their utility in imaging or therapy applications.

Role of papillary muscle in the generation and maintenance of reentry during ventricular tachycardia and fibrillation in isolated swine right ventricle

BACKGROUND

The role of papillary muscle (PM) in the generation and maintenance of reentry is unclear.

METHODS AND RESULTS

Computerized mapping (477 bipolar electrodes, 1.6-mm resolution) was performed in fibrillating right ventricles (RVs) of swine in vitro. During ventricular fibrillation (VF), reentrant wave fronts often transiently anchored to the PM. Tissue mass reduction was then performed in 10 RVs until VF converted to ventricular tachycardia (VT). In an additional 6 RVs, procainamide infusion converted VF to VT. Maps showed that 77% (34 of 44) of all VT episodes were associated with a single reentrant wave front anchored to the PM. Purkinje fiber potentials preceded the local myocardial activation, and these potentials were recorded mostly around the PM. When PM was trimmed to the level of endocardium (n = 4), sustained VT was no longer inducible. Transmembrane potential recordings (n = 5) at the PM revealed full action potential during pacing, without evidence of ischemia. Computer simulation studies confirmed the role of PM as a spiral wave anchoring site that stabilized wave conduction.

CONCLUSIONS

We conclude that PM is important in the generation and maintenance of reentry during VT and VF.

An advanced algorithm for solving partial differential equation in cardiac conduction

An advanced integration method for solving reaction-diffusion-type equations for cardiac conduction is suggested. Operator splitting and adaptive time step methods were used in this method, which can significantly speed up integration while preserving accuracy.

Spatiotemporal heterogeneity in the induction of ventricular fibrillation by rapid pacing: importance of cardiac restitution properties

The mechanism by which rapid pacing induces ventricular fibrillation (VF) is unclear. We performed computerized epicardial mapping studies in 10 dogs, using 19-beat pacing trains. The pacing interval (PI) of the first train was 300 ms and then was progressively shortened until VF was induced. For each PI, we constructed restitution curves for the effective refractory period (ERP). When the PI was long, the activation cycle length (CL) was constant throughout the mapped region. However, as the PI shortened, there was an increase in the spatiotemporal complexity of the CL variations and an increase in the slope of the ERP restitution curve. In 5 dogs, we documented the initiation of VF by wavebreak at the site of long-short CL variations. Computer simulation studies using the Luo-Rudy I ventricular action potential model in simulated 2-dimensional tissue reproduced the experimental results when normal ERP and conduction velocity (CV) restitution properties were intact. By altering CV and ERP restitutions in this model, we found that CV restitution creates spatial CL variations, whereas ERP restitution underlies temporal, beat-to-beat variations in refractoriness during rapid pacing. Together, the interaction of CV and ERP restitutions produces spatiotemporal oscillations in cardiac activation that increase in amplitude as the PI decreases, ultimately causing wavebreak at the site of intrinsic heterogeneity. This initial wavebreak then leads to the formation of spiral waves and VF. These findings support a key role for both CV and ERP restitutions in the initiation of VF by rapid pacing.

Chaos and the transition to ventricular fibrillation: a new approach to antiarrhythmic drug evaluation

Sudden cardiac death resulting from ventricular fibrillation can be separated into 2 components: initiation of tachycardia and degeneration of tachycardia to fibrillation. Clinical drug studies such as CAST and SWORD demonstrated that focusing exclusively on the first component is inadequate as a therapeutic modality. The hope for developing effective pharmacological therapy rests on a comprehensive understanding of the second component, the transition from tachycardia to fibrillation. We summarize evidence that the transition from tachycardia to fibrillation is a transition to spatiotemporal chaos, with similarities to the quasiperiodic transition to chaos seen in fluid turbulence. In this scenario, chaos results from the interaction of multiple causally independent oscillatory motions. Simulations in 2-dimensional cardiac tissue suggest that the destabilizing oscillatory motions during spiral-wave reentry arise from restitution properties of action potential duration and conduction velocity. The process of spiral-wave breakup in simulated cardiac tissue predicts remarkably well the sequence by which tachycardia degenerates to fibrillation in real cardiac tissue. Modifying action potential duration and conduction velocity restitution characteristics can prevent spiral-wave breakup in simulated cardiac tissue, suggesting that drugs with similar effects in real cardiac tissue may have antifibrillatory efficacy (the Restitution Hypothesis). If valid for the real heart, the Restitution Hypothesis will support a new paradigm for antiarrhythmic drug classification, incorporating an antifibrillatory profile based on effects on cardiac restitution and the traditional antitachycardia profile (classes 1 through 4).

Mechanical properties of trabecular bone in the human mandible: implications for dental implant treatment planning and surgical placement

PURPOSE

This study sought to establish the relationships between bone density, elastic modulus, and ultimate compressive strength of trabecular bone in the human mandible, and to determine the influence that the cortical plates have on these values.

MATERIALS AND METHODS

Nine fresh-frozen human mandibles between the ages of 56 and 90 years were cut into anterior (incisors and canine), middle (premolars), and distal (molars) sections. Seventy-six cylindrical trabecular bone specimens with bone marrow in situ were then prepared and tested in compression in the vertical direction. These tests were performed at a constant strain rate of 0.01 s(-1) with and without the presence of the cortical plates.

RESULT

The density of mandibular trabecular specimens with bone marrow in situ ranged from 0.85 to 1.53 g/cm3, with a mean value of 1.14 g/cm3 (SD = 0.15). With the cortical plates present, the elastic modulus ranged from 24.9 to 240.0 megapascals (MPa), with a mean value of 96.2 MPa (standard deviation (SD) = 40.6). Without the cortical plates present, the elastic modulus ranged from 3.5 to 125.6 MPa, with a mean value of 56.0 MPa (SD = 29.6). The ultimate compressive strength of the trabecular bone ranged from 0.22 to 10.44 MPa, with a mean value of 3.9 MPa (SD = 2.7).

CONCLUSION

This study indicates that the trabecular bone in the human mandible possesses significantly higher density, elastic modulus, and ultimate compressive strength in the anterior region than in either the middle or distal regions. The absence of cortical plates decreases the bone elastic modulus. These findings quantitatively confirm the need for clinical awareness in altering implant treatment plans and/or design in relation to bone density and the presence of the cortical plates.

Identification of a critical motif responsible for gating of Kir2.3 channel by intracellular protons

Protons are involved in gating Kir2.3. To identify the molecular motif in the Kir2.3 channel protein that is responsible for this process, experiments were performed using wild-type and mutated Kir2. 3 and Kir2.1. CO2 and low pHi strongly inhibited wild-type Kir2.3 but not Kir2.1 in whole cell voltage clamp and excised inside-out patches. This CO2/pH sensitivity was completely eliminated in a mutant Kir2.3 in which the N terminus was substituted with that in Kir2.1, whereas a similar replacement of its C terminus had no effect. Site-specific mutations of all titratable residues in the N terminus, however, did not change the CO2/pH sensitivity. Using several chimeras generated systematically in the N terminus, a 10-residue motif near the M1 region was identified in which only three amino acids are different between Kir2.3 and Kir2.1. Mutations of these residues, especially Thr53, dramatically reduced the pH sensitivity of Kir2.3. Introducing these residues or even a single threonine to the corresponding positions of Kir2.1 made the mutant channel pH-sensitive. Thus, a critical motif responsible for gating Kir2.3 by protons was identified in the N terminus, which contained about 10 residues centered by Thr53.

Suppression of Kir2.3 activity by protein kinase C phosphorylation of the channel protein at threonine 53

Kir2.3 plays an important part in the maintenance of membrane potential in neurons and myocardium. Identification of intracellular signaling molecules controlling this channel thus may lead to an understanding of the regulation of membrane excitability. To determine whether Kir2.3 is modulated by direct phosphorylation of its channel protein and identify the phosphorylation site of protein kinase C (PKC), we performed experiments using several recombinant and mutant Kir2.3 channels. Whole-cell Kir2.3 currents were inhibited by phorbol 12-myristate 13-acetate (PMA) in Xenopus oocytes. When the N-terminal region of Kir2.3 was replaced with that of Kir2.1, another member in the Kir2 family that is insensitive to PMA, the chimerical channel lost its PMA sensitivity. However, substitution of the C terminus was ineffective. Four potential PKC phosphorylation sites in the N terminus were studied by comparing mutations of serine or threonine with their counterpart residues in Kir2.1. Whereas substitutions of serine residues at positions 5, 36, and 39 had no effect on the channel sensitivity to PMA, mutation of threonine 53 completely eliminated the channel response to PMA. Interestingly, creation of this threonine residue at the corresponding position (I79T) in Kir2.1 lent the mutant channel a PMA sensitivity almost identical to the wild-type Kir2.3. These results therefore indicate that Kir2.3 is directly modulated by PKC phosphorylation of its channel protein and threonine 53 is the PKC phosphorylation site in Kir2.3.

[Long-term follow-up of combined therapy with large-dose zinc sulfate and low-dose penicillamine in children with hepatolenticular degeneration]

OBJECTIVE

To summarize the long-term effect of combined treatment with large-dose zinc sulfate and low-dose penicillamine in children with hepatolenticular degeneration (HLD).

METHODS

The patients who had symptoms were treated with large-dose zinc sulfate (100-150mg, <6yr; 150-200mg, 6-8yr; 200-300mg, 9-10yr; 300mg,>10yr; 3 times a day) in addition to low-dose penicillamine(8-10mg/kg/d) at the beginning of treatment. Zinc sulfate alone was given to the presymptomatic patients and it was used as maintenance therapy when clinical improvement was obtained. 31 children were followed up for 4-11 years.

RESULTS

In 3 presymptomatic patients, no clinical abnormalities were found. Among 28 patients with symptoms, 23 patients (82%) had their symptoms and signs subsided or much improved, 2 patients(7%) remained unchanged, and 3(11%) died. Blood concentrations of copper were persistently lower than normal. Urine copper excretion of 24 hours was significantly lower than that before the combined therapy in all patients, and it became normal in 5 cases(16%) after 6 months of treatment, and in 26 cases(84%) after 1-2 years of treatment. Higher blood concentrations of zinc were found in 20 cases(65%), and higher urine zinc excretion was noted in 25 cases(81%) once or more times during the therapy.

CONCLUSION

Combined therapy of large-dose zinc sulfate and low-dose penicillamine is an effective, safe and cheap treatment for children with HLD.

Mechanism of acceleration of functional reentry in the ventricle: effects of ATP-sensitive potassium channel opener

BACKGROUND

The effect of effective refractory period (ERP) shortening on the vulnerability and characteristics of induced functional reentry in the ventricle remain poorly defined. We hypothesized that ERP shortening increases ventricular vulnerability to reentry and accelerates its rate, as is the case in the atrium.

METHODS AND RESULTS

The epicardial surfaces of 19 isolated and superfused canine right ventricular slices (4x4 cm and <2 mm thick) were mapped with 480 bipolar electrodes 1.6 mm apart. Vulnerability was tested during pacing at a cycle length (CL) of 600 ms and with a single premature stimulus of 5-ms duration at increasing current strength of 1 to 100 mA. Cromakalim (10 micromol/L), an ATP-sensitive potassium channel opener, caused a significant (P<0. 001) shortening of the ERP but had no effect on conduction velocity. Cromakalim increased (P<0.01) the vulnerability (product of current and the stimulus coupling interval) for reentry induction. Reentry had a significantly shorter CL and lasted for a longer duration (P<0. 001). The central core around which the wave front rotated became smaller, which caused shortening of the CL of reentry. A significant (P<0.001) linear correlation was found between core size and reentry CL. These effects of cromakalim were reversible. Two-dimensional simulation studies using the modified Luo-Rudy I model of cardiac action potential, in which the refractory period was variably shortened by a progressive increase of the time-independent potassium conductance, reproduced the experimental findings.

CONCLUSIONS

ERP shortening by an ATP-sensitive potassium channel opener increases ventricular vulnerability to reentry and accelerates its rate by decreasing the core size around which the wave front rotates.

[Cloning and sequencing analysis of rice stripe virus genome segment 4 of Chinese isolate Y]

The cDNA fragment covering full-length sequence of RStV RNA4 of Yunnan isolate in China was obtained by RT-PCR. The PCR-derived fragment was then cloned into vector pCRII. The cloned cDNA was sequenced. Comparison of the nucleotide and deduced amino acid sequences with those of the Japanese isolate T was made. The results showed that at the nucleotides level, vORF, vcORF and the intergenic region had 94.9%, 94.1% and 86.1% identity respectively, the 5'-untranslational region was exactly the same as that of Japanese isolate T, while the 3'-terminal sequence had 96.1% identity, differing by two nucleotides; at the amino acid level, vORF and vcORF had 99.4% and 98.3% identity respectively. Therefore, as well as being exactly the same size for the two isolates, the amino acid sequences of the coding regions and the 5'- and 3'-terminal sequences were well conserved. Our results indicated that the Chinese isolate is closely related to the Japanese isolate T.

Detection of PERIOD/PAS-binding proteins from rat brain nuclear extracts by affinity chromatography

In Drosophila, period and timeless gene's products (dPER and dTIM) have been identified to act as circadian clock components in heterodimeric form. The formation of dPER-dTIM complex is based on the interaction between dPER's PAS domain and dTIM's PAS binding domain. As an initial step to understand the molecular mechanism of mammalian circadian clock, we screened His-tagged dPER/PAS binding proteins from rat brain nuclear extracts, using Ni2+-NTA affinity chromatography. As a result of screening, we identified two proteins (192 and 180 kDa), which specifically bound to His-dPER/PAS in rat brain extracts. Such proteins might be a candidate of rat timeless proteins.

Cardiac electrical restitution properties and stability of reentrant spiral waves: a simulation study

Spiral wave breakup is a proposed mechanism underlying the transition from ventricular tachycardia to fibrillation. We examined the importance of the restitution of action potential duration (APD) and of conduction velocity (CV) to the stability of spiral wave reentry in a two-dimensional sheet of simulated cardiac tissue. The Luo-Rudy ventricular action potential model was modified to eliminate its restitution properties, which are caused by deactivation or recovery from inactivation of K+, Ca2+, and Na+ currents (IK, ICa, and INa, respectively). In this model, we find that 1) restitution of ICa and INa are the main determinants of the steepness of APD restitution; 2) for promoting spiral breakup, the range of diastolic intervals over which the APD restitution slope is steep is more important than the maximum steepness; 3) CV restitution promotes spiral wave breakup independently of APD restitution; and 4) "defibrillation" of multiple spiral wave reentry is most effectively achieved by combining an antifibrillatory intervention based on altering restitution with an antitachycardia intervention. These findings suggest a novel paradigm for developing effective antiarrhythmic drugs.

Preparation and mechanical properties of dense polycrystalline hydroxyapatite through freeze-drying

High purity hydroxyapatite (HAp) powders were synthesized through the wet-chemical method and subsequent freeze-drying or heat-drying, respectively. Dense polycrystalline HAp ceramics were obtained by sintering the powder compacts in air in the temperature range 1100-1350 degrees C. Results show that the freeze-drying method can produce highly homogeneous, fine-grained HAp powders. The relative density, Vickers hardness and flexural strength of the sintered freeze-dried HAp ceramics increased with the sintering temperature, reaching a maximum at around 1350 degrees C, and the highest values obtained were 99.0%, 820 and 110 MPa, respectively. All these mechanical properties of the freeze-dried HAp ceramics are much higher than those of the conventionally heat-dried HAp ceramics. The drying method can significantly influence the properties of the HAp powders as well as the HAp ceramics.

Expression of basic fibroblast growth factor in nasal polyps

Basic fibroblast growth factor (bFGF) is a polypeptide that is mitogenic for a wide variety of cell types. We used Northern blot analysis and immunohistochemistry to determine if bFGF is expressed in the nasal polyp tissue; bFGF messenger RNA was detectable in the polyps examined by Northern blot analysis. Strong immunostaining for bFGF was found in blood vessels and along the basement membrane of the epithelial cell layers. Basal epithelial cells and some infiltrating mononuclear cells also stained for bFGF. Proliferating cell nuclear antigen colocalized with bFGF to basal epithelial cells, endothelial cells, and areas of focal epithelial metaplasia. The polyp tissue was double-labeled with a mouse monoclonal antitryptase, a specific mast cell marker, and anti-bFGF. A significant number (65% +/- 19%) of the bFGF-positive mononuclear cells in the polyp tissues were positive for tryptase. These findings suggest that bFGF may contribute to the endothelial and epithelial proliferation in nasal polyp tissues and that mast cells are one source of this growth factor.

Ultrastructural immunolocalization of basic fibroblast growth factor in mast cell secretory granules. Morphological evidence for bfgf release through degranulation

We previously reported that mast cells (MCs) serve as a source of basic fibroblast growth factor (bFGF), a potent angiogenic and mitogenic polypeptide, suggesting that bFGF may mediate MC-related neovascularization and fibroproliferation. Unlike many other growth factors, bFGF lacks a classic peptide sequence for its secretion, and the mechanism(s) for its release remains controversial. Because MCs release a wide spectrum of bioactive products via degranulation, we hypothesized that MC degranulation may be a mechanism of bFGF release and used ultrastructural immunohistochemistry to test the hypothesis. We reasoned that if bFGF is released through degranulation, it should be localized to MC secretory granules. Human tissues with chronic inflammation and rat/mouse tissues with anaphylaxis were studied. In all tissue samples examined, positive staining (or immunogold particle localization) for bFGF in MCs was predominantly in the cytoplasmic granules. Moderate bFGF immunoreactivity was also found in the nucleus, whereas the cytosol and other subcellular organelles exhibited minimal immunogold particle localization. In contrast, no immunogold particle localization for bFGF was observed in lymphocytes or plasma cells. In rat/mouse lingual tissue undergoing anaphylaxis, immunogold particle localization for bFGF was found not only in swollen cytoplasmic granules but also in the extruded granules of MCs. Three different anti-bFGF antibodies gave similar immunogold particle localization patterns, whereas all controls were negative. These results provide morphological evidence suggesting that, despite the lack of a classic secretory peptide in its structure, bFGF is localized to the secretory granules in MCs and may be released through degranulation.

Fibroproliferation and mast cells in the acute respiratory distress syndrome

BACKGROUND

Mast cells (MCs), which are a major source of cytokines and growth factors, have been implicated in various fibrotic disorders. To clarify the contribution of MCs to fibrogenesis, lung tissue from patients with the acute respiratory distress syndrome (ARDS) was examined during exudative through to fibroproliferative stages.

METHODS

Lung tissue was obtained from 17 patients with ARDS who had pathological features of the early exudative stage (n = 6) or the later reparative stages (n = 11), from four patients with idiopathic pulmonary fibrosis, and from three patients with normal lung tissue. Immunohistochemical localisation of tryptase (found in all human MCs), chymase (found in a subset of human MCs), alpha-smooth muscle actin (identifies myofibroblasts), and procollagen type I was performed.

RESULTS

Normal lung tissue exhibited myofibroblast and procollagen type I immunolocalisation scores each of < 5 and MC scores of 1. Increased scores were defined as myofibroblast and procollagen type I scores of > 10 and MC scores of > or = 2. Eighty percent of lung tissue samples from the early exudative stage of ARDS exhibited increased numbers of myofibroblasts, 50% had increased numbers of procollagen type I producing cells, while only 17% had increased numbers of MCs compared with control samples. All samples from the later reparative stages of ARDS had increased numbers of myofibroblasts and procollagen type I producing cells. Increased numbers of MCs were seen in 55% of samples from the reparative stages. There was no significant shift in MC phenotype in the ARDS samples.

CONCLUSIONS

Increased numbers of myofibroblasts and procollagen type I producing cells were frequently found early in the course of ARDS. MC hyperplasia was unusual during this stage, but was often a feature of the later reparative stages. MCs do not appear to initiate fibroproliferation in ARDS.

Development of approaches to improve cell survival in myoblast transfer therapy

Myoblast transplantation has been extensively studied as a gene complementation approach for genetic diseases such as Duchenne Muscular Dystrophy. This approach has been found capable of delivering dystrophin, the product missing in Duchenne Muscular Dystrophy muscle, and leading to an increase of strength in the dystrophic muscle. This approach, however, has been hindered by numerous limitations, including immunological problems, and low spread and poor survival of the injected myoblasts. We have investigated whether antiinflammatory treatment and use of different populations of skeletal muscle-derived cells may circumvent the poor survival of the injected myoblasts after implantation. We have observed that different populations of muscle-derived cells can be isolated from skeletal muscle based on their desmin immunoreactivity and differentiation capacity. Moreover, these cells acted differently when injected into muscle: 95% of the injected cells in some populations died within 48 h, while others richer in desmin-positive cells survived entirely. Since pure myoblasts obtained from isolated myofibers and myoblast cell lines also displayed a poor survival rate of the injected cells, we have concluded that the differential survival of the populations of muscle-derived cells is not only attributable to their content in desmin-positive cells. We have observed that the origin of the myogenic cells may influence their survival in the injected muscle. Finally, we have observed that myoblasts genetically engineered to express an inhibitor of the inflammatory cytokine, IL-1, can improve the survival rate of the injected myoblasts. Our results suggest that selection of specific muscle-derived cell populations or the control of inflammation can be used as an approach to improve cell survival after both myoblast transplantation and the myoblast-mediated ex vivo gene transfer approach.

Role of pectinate muscle bundles in the generation and maintenance of intra-atrial reentry: potential implications for the mechanism of conversion between atrial fibrillation and atrial flutter

To determine the role of pectinate muscle (PM) bundles in the formation of intra-atrial reentry, 10 isolated canine right atrial tissues were perfused with Tyrode's solution containing 1 to 2.5 micromol/L acetylcholine (ACh). The endocardium was mapped using 477 bipolar electrodes with 1.6-mm resolution. Reentry was induced by a premature stimulus (S2). Computer simulation studies were used to investigate the importance of regional myocardial thickness in reentry formation. A total of 40 episodes of reentry were induced; 28 episodes were stationary, and the remaining 12 were nonstationary. The stationary reentry was induced either immediately after the S2 stimuli (n=9) or after an initial period of irregular activations that lasted 1460+/-1077 ms (n= 19). Of 28 episodes, 20 were initiated by conduction block along large PM ridges, leading to wave break and the initiation of reentry. The reentrant wave fronts remained stationary and rotated around these ridges as anchoring sites. During the transition from the initial irregular activations to stationary reentry, the electrogram morphology converted from "fibrillation-like" to "flutter-like" activity. In 8 episodes, initially stationary reentry converted to irregular activations because of interference with outside wave fronts (n=5) or spontaneous separation of waves from the ridges (n=3). Compared with stationary reentry, nonstationary reentry always occurred over an area without large PMs, and the mean life span was much shorter (102+/-151 versus 3.8+/-1.1 rotations, P<0.001). Computer simulation studies showed that a critical ridge thickness is needed for reentry to anchor, thereby converting fibrillation to flutter. We conclude that PM ridge forms an area where wave break occurs, allowing the initiation of reentry. It also provides a natural anchor to the reentrant wave front, lengthening the life span of reentry. The attachment and detachment of the reentrant wave front to and from the ridge determine "flutter-like" or "fibrillation-like" activity.

The transcriptional corepressor NAB2 inhibits NGF-induced differentiation of PC12 cells

The PC12 pheochromocytoma cell line responds to NGF by undergoing growth arrest and proceeding to differentiate toward a neuronal phenotype. Among the early genetic events triggered by NGF in PC12 cells are the rapid activation of the zinc finger transcription factor Egr1/NGFI-A, and a slightly delayed induction of NAB2, a corepressor that inhibits Egr1 transcriptional activity. We found that stably transfected PC12 cells expressing high levels of NAB2 do not differentiate, but rather continue to proliferate in response to NGF. Inhibition of PC12 differentiation by NAB2 overexpression was confirmed using two additional experimental approaches, transient transfection, and adenoviral infection. Early events in the NGF signaling cascade, such as activation of MAP kinase and induction of immediate-early genes, were unaltered in the NAB2-overexpressing PC12 cell lines. However, induction of delayed NGF response genes such as TGF-beta1 and MMP-3 was inhibited. Furthermore, NAB2 overexpression led to downregulation of p21(WAF1), a molecule previously shown to play a pivotal role in the ability of PC12 cells to undergo growth arrest and commit to differentiation in response to NGF. Cotransfection with p21(WAF1) restored the ability of NAB2-overexpressing PC12 cells to differentiate in response to NGF.

Cultured human trabecular meshwork cells express functional growth factor receptors

PURPOSE

To compare the mRNA expression of growth factor receptors in cultured human trabecular meshwork (HTM) cells with ex vivo HTM tissues and to determine whether HTM cells generate a physiologic response after exposure to exogenous growth factors.

METHODS

The reverse transcription-polymerase chain reaction (RT-PCR) method was used to detect the expression of various growth factor receptor mRNAs using early passaged, cultured HTM cells from donors of several ages. RT-PCR on ex vivo HTM tissues from healthy donors and donors with glaucoma were also used to compare and contrast mRNA expression with cell culture results. After the exogenous administration of growth factors, cell proliferation and extracellular acidification rate studies were used to measure the functional responses of HTM cells to growth factors.

RESULTS

Amplification products of the expected size for 15 growth factor receptors were detected in cultured HTM cells and in ex vivo HTM tissues. The administration of exogenous growth factors showed that (a) hepatocyte growth factor (HGF), epidermal growth factor (EGF), insulinlike growth factor (IGF)-1, tumor necrosis factor (TNF) alpha, platelet-derived growth factor (PDGF)-AA, PDGF-BB, PDGF-AB, and basic fibroblast growth factor (FGF-2) stimulated cell proliferation, whereas FGF-1 (acidic), transforming growth factor (TGF) alpha, interleukin (IL)-1alpha, nerve growth factor (NGF), and FGF-7 (keratinocyte growth factor [KGF]) had no significant influence on cell proliferation; (b) TGF-beta isoforms significantly inhibited EGF-stimulated trabecular meshwork cell proliferation; and (c) FGF-1 (acidic), TGF-alpha, EGF, IL-1alpha, IL-1beta, HGF, TNF-alpha, PDGF-AA, and IGF-1 significantly stimulated extracellular acidification, whereas FGF-2 (basic), FGF-7 (KGF), TGF-beta1-beta3 and NGF had no significant influence on extracellular acidification.

CONCLUSIONS

These studies show that mRNA for numerous growth factor receptors can be detected in cultured HTM cells and in ex vivo HTM tissues. They also show that many of the receptors are functional, because exogenous growth factor administration elicits a physiologic response. In vivo, these receptors may be activated by growth factors present within the aqueous humor (aquecrine/paracrine) or by growth factors synthesized and released locally by trabecular meshwork cells themselves (autocrine). Specific growth factors acting through high-affinity receptors may be involved in maintaining the normal microenvironment of the HTM and also may be involved in the pathogenesis of primary open-angle glaucoma.

[Study on the determination of trace mercury in foods by circulating enrichment-cold vapour atomic absorption spectrometry]

The determination of trace mercury using the self-developed circulating enrichment apparatus with cold vapour atomic absorption spectrometry was investigated. Various experimental conditions were discussed and optimized. The effect of interferences was examined. The developed method is sensitive, accurate, simple and available and has already been used in the analysis of various kinds of food samples and national standard reference materials, and the results obtained were satisfactory.

[Construction and application of retroviral vector carrying green fluorescent protein]

OBJECTIVE

To construct retroviral vector carrying rapidly selective marker.

METHODS

The recombination retroviral vector GCGFPPXSN was constructed by cloning the green fluorescent protein (GFP) cDNA into the retroviral vector containing putative internal ribosome entry sites GCXPXSN and transferred in ecotropic packaging cell line PE501 by electroporation method. The supernatants of the PE501GCGFPPXSN were used to infect the amphotropic packaging cell line PA317. The G418 resistant clones were selected in 4 weeks and were detectable by fluorescence microscopy or by fluorescence-activated cell sorting(FACS).

RESULTS

A recombination retroviral vector GCGFPPXSN carrying rapidly selective marker GFP was constructed. GFP expression in packaging cell line PA317-GCGFPPXSN transferred by GCGFPPXSN was detected by fluorescence microscopy of FACS. PA317-GCGFPPXSN grew to a titer of 1.2 x 10(5) cpu/ml. By cocultivating retroviral vector producing cells and T lymphocytes, expression of GFP was observed in T lymphocytes 2 days after the end of the cocultivation. T lymphocytes expressing GFP were separated.

CONCLUSION

The mammalian cell can be efficient gene transfected by retroviral vector carrying GFP. The use of GFP for cell marking represents an important advantage over conventional strategies which typically involve the use of neomycin resistance. GFP, in fact, allows a rapid in vitro selection of transduced cell by FACS. The selection requires only two-day culture with this retroviral vector, compared with 10-14 day culture with a classical retroviral vector.

Mapping of Rpb3 and Rpb5 contact sites on two large subunits, Rpb1 and Rpb2, of the RNA polymerase II from fission yeast

[Rpb1 and Rpb2] Mapping of the contact sites on two large subunits of the fission yeast Schizosaccharomyces pombe RNA polymerase II with two small subunits, Rpb3 and Rpb5, was carried out using the two-hybrid screening system in the budding yeast Saccharomyces cerevisiae. Rpb5 was found to interact with any fragment of Rpb1 that contained the region H, which is conserved among the subunit 1 homologues of all RNA polymerases, including the beta' subunit of prokaryotic RNA polymerases. In agreement with the fact that Rpb5 is shared among all three forms of eukaryotic RNA polymerases, the region H of RNA polymerase I subunit 1 (Rpa190) was also found to interact with Rpb5. On the other hand, two-hybrid screening of Rpb2 fragments from RNA polymerase II indicated the presence of an Rpb3 contact site in the region H which is conserved among the subunit 2 homologues of all RNA polymerases, including the beta subunit of prokaryotic RNA polymerases. Possible functions of the regions H in the subunits 1 and 2 are discussed.

[Effects of oxidatively modified lipoproteins on the expression of monocyte chemoattractant protein-1 in endothelial cells]

OBJECTIVE

To clarify whether lipoproteins, particularly oxidatively modified low density lipoprotein (OX-LDL) and very low density lipoprotein (OX-VLDL) play a role in the express of monocyte chemoattractant protein-1 (MCP-1) mRNA and protein in endothelial cells (ECs).

METHODS

After a 24-hour exposure to LDL, OX-LDL, VLDL and OX-VLDL respectively the total RNA in call aorta ECs was extracted by means of guanidinium isothiocyanate method. MCP-1 mRNA expression in ECs was examined by dot blot analysis using a gamma-32P-end-labelled 35 mer oligonucleotide probe of MCP-1. Meanwhile, MCP-1 protein in EC conditioned media (EC-CM) of each group was determined by sandwich ELISA, and MCP-1 protein in ECs was examined immunocytochemically as well.

RESULTS

Cultured calf aorta ECs expressed MCP-1 mRNA and protein, and OX-LDL and OX-VLDL induced further a strong expression of MCP-1 mRNA, and an increased MCP-1 protein level in EC-CM. The expression of MCP-1 mRNA and protein was only slightly increased when exposed to LDL and VLDL, and immunohistological staining with polyclonal MCP-1 antibody give a similar result.

CONCLUSION

OX-LDL and OX-VLDL are able to induce a strong expression of MCP-1 in ECs.

[Study on determination of poisonous heavy metal element lead by graphite furnace atomic absorption spectrometry]

In this paper, the determination of trace lead in foods by optical temperature control GFAAS was studied. The method was certified by the analysis of the national standard reference materials.

Erythrocyte defenses against hydrogen peroxide: the role of ascorbic acid

Ascorbate has been reported to increase intracellular hydrogen peroxide (H2O2) generation in human erythrocytes. In the present work, the basis for this prooxidant effect of the vitamin was investigated in the context of erythrocyte defenses against H2O2. Ascorbate added to erythrocytes caused a dose-dependent increase in intracellular H2O2, which was measured as inactivation of endogenous catalase in the presence of 3-amino-1,2,4-triazole (aminotriazole). Ascorbate-induced catalase inactivation was not observed when only the intracellular ascorbate concentration was increased, when cells were incubated with ascorbate in plasma, or when extracellular Fe3+ was chelated. Together, these results suggest that the observed ascorbate-induced H2O2 generation is due to Fe3+-catalyzed oxidation of extracellular, as opposed to intracellular, ascorbate by molecular oxygen. Rather than generate an oxidant stress in erythrocytes, ascorbate was one of the most sensitive intracellular antioxidants to H2O2 coming from outside the cells. On the other hand, intracellular ascorbate contributed little to the detoxification of H2O2, which was found to be mediated by both catalase and by the GSH system.

Carbohydrates engineered at antibody constant domains can be used for site-specific conjugation of drugs and chelates

To improve the efficiency of site-specific conjugation of chelates and drugs to antibodies, and to minimize the incidence of immunoreactivity perturbation to the resultant immunoconjugates, Asn-linked oligosaccharide moieties were designed and engineered into the constant domains of a humanized anti-CD22 monoclonal antibody, hLL2. From 10 potential glycosylation mutants, two CH1 domain glycosylation sites, HCN1 and HCN5, were identified that were positioned favorably for glycosylation. The carbohydrate (CHO) chains attached at these sites were differentially processed so that HCN5-CHOs were physically larger than HCN1-CHOs. Although both the CH1-appended CHOs, and the LL2 Vkappa-appended CHOs conjugated efficiently with small chelates, the HCN5-CHOs, due to the structural and positional superiority, appear to be a better conjugation site for large drug complexes, such as 18 kDa doxorubicin (DOX)-dextran.

[Perforin and Fas-ligand expression of tumor infiltrating lymphocytes in human hepatocellular carcinoma]

OBJECTIVE

To investigate perforin and Fas-ligand (Fas-L) expression of tumor infiltrating lymphocytes (TIL) in human hepatocellular carcinoma (HCC).

METHODS

Expression of perforin and Fas-L of TIL was studied in 20 HCC cases using in situ hybridization and immunohistochemistry.

RESULTS

Expression of perforin and Fas-L gene were detected in TIL in 80% of the cases studied. Among them, one patient (no. 14) in whom expression of perforin and Fas-L were noticed in the majority of the TIL, had no recurrence of HCC for one and one half (1.5) year after tumor resection. It indicates that presence of large number of activated T cells might be beneficial for the tumor therapy. In the remaining cases, only 10% of TIL were obtained able to express perforin and Fas-L indicating that only a few TIL were activated and cytotoxic to HCC.

CONCLUSIONS

Even there were a multitude of T cells infiltrating in HCC, only few of them were immunoactived and to be cytotoxic to HCC. It seems important to adopt measures in order to promote further proliferation of these activated T cells either in vitro or in vivo.

Interaction of Oct-1 and automodification domain of poly(ADP-ribose) synthetase

We isolated several clones from a matchmaker two-hybrid system human lymphocyte cDNA library using an automodification domain of poly(ADP-ribose) synthetase (PARS) as a probe. A DNA sequence (approximately 1 kbp) of the clone was identical to part of the Oct-1 DNA sequence. We then constructed either a His-tagged or GST fusion protein of the inserted cDNA from the clone and the fusion protein was shown to interact with PARS by far-Western blot analysis and co-precipitation with affinity resin. Furthermore, the His-tagged Oct-1/POU-homeo fusion protein interacted weakly with the octamer motif of the DRa promoter and the addition of PARS fusion protein greatly increased the DNA binding activity. These results suggest that PARS interacts with Oct-1 and stabilizes the binding of Oct-1 to the octamer motif.

Effects of dietary protein and tumor necrosis factor on components of the insulin-like growth factor-I pathway in the colon and small intestine in protein-depleted rats

Intestinal cell growth is markedly affected by nutrient intake and the presence of cytokines. Since insulin-like growth factor-I (IGF-I) is an important hormone regulator of intestinal proliferation, this study examined the effects of dietary protein content and tumor necrosis factor (TNF) on mRNA levels of IGF-I, IGF-I receptor, IGF binding protein-3 (IGFBP-3), and IGFBP-4 and on the histology of the colon, jejunum, and ileum in protein-malnourished rats. After 2 weeks of feeding a 2% casein diet, rats continued on the 2% casein diet or were refed with a 20% casein diet and received daily intraperitoneal injections of either TNF (50 microg/kg) or saline for 4 days. The abundance of mRNA in the intestine was determined by RNA dot-blot analysis, and morphology measurements were performed by light microscopy. Simultaneous refeeding with the 20% casein diet and administration of TNF led to a modest increase in IGF-I and IGFBP-4 mRNA abundance in the colon. However, in the jejunum and ileum, refeeding had no effect but TNF caused a decrease in IGF-I and IGFBP-3 mRNA levels in malnourished rats. Refeeding with the 20% casein diet resulted in relatively modest histologic changes, which were greater in the colon versus the small intestine. The decreased magnitude of histologic changes in the order of the colon, ileum, and jejunum may reflect a response to a gradient of amino acid availability from intraluminal nutrients. These data demonstrate that TNF has distinct effects on colon and small intestine mRNA, but these mild changes had only a slight impact in the colon and did not translate into identifiable histologic changes in the small intestine. Combined protein restriction and TNF administration had only a modest effect on intestinal mRNA levels and mucosal histology.