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T T Liu

Publications and source records attributed to T T Liu.

At least 19 recordsLinked to original sources
PubMed2006

Quantification of regional pulmonary blood flow using ASL-FAIRER.

Pulsed arterial spin labeling (ASL) techniques have been theoretically and experimentally validated for cerebral blood flow (CBF) quantification. In this study ASL-FAIRER was used to measure regional pulmonary blood flow (rPBF) in seven healthy subjects. Two general ASL strategies were investigated: 1) a single-subtraction approach using one tag-control pair acquisition at an inversion time (TI) matched to the RR-interval, and 2) a multiple-subtraction approach using tag-control pairs acquired at various TIs. The mean rPBF averaged 1.70 +/- 0.38 ml/min/ml when measured with the multiple-subtraction approach, and was approximately 2% less when measured with the single-subtraction method (1.66 +/- 0.24 ml/min/ml). Assuming an average lung density of 0.33 g/ml, this translates into a regional perfusion of approximately 5.5 ml/g/min, which is comparable to other measures of pulmonary perfusion. As with other ASL applications, a key problem with quantitative interpretation of the results is the physical gap between the tagging region and imaged slice. Because of the high pulsatility of PBF, ASL acquisition and data analysis differ significantly between the lung and the brain. The advantages and drawbacks of the single- vs. multiple-subtraction approaches are considered within a theoretical framework tailored to PBF.

Adult↗
PubMed2001

Ion selectivities of the Ca(2+) sensors for exocytosis in rat phaeochromocytoma cells.

1. The ion selectivities of the Ca(2+) sensors for the two components of exocytosis in rat phaeochromocytoma (PC12) cells were examined by measurement of membrane capacitance and amperometry. The cytosolic concentrations of metal ions were increased by photolysis of caged-Ca(2+) compounds and measured with low-affinity indicators benzothiazole coumarin (BTC) or 5-nitrobenzothiazole coumarin (BTC-5N). 2. The Ca(2+)-induced increases in membrane capacitance comprised two phases with time constants of 30--100 ms and 5 s. Amperometric events reflecting the exocytosis of large dense-core vesicles occurred selectively in the slow phase, even with increases in the cytosolic Ca(2+) concentration of > 0.1 mM. 3. The slow component of exocytosis was activated by all metal ions investigated, including Cd(2+) (median effective concentration, 18 pM), Mn(2+) (500 nM), Co(2+) (900 nM), Ca(2+) (8 microM), Sr(2+) (180 microM), Ba(2+) (280 microM) and Mg(2+) (> 5 mM). In contrast, the fast component of exocytosis was activated by Cd(2+) (26 pM), Mn(2+) (620 nM), Ca(2+) (24 microM) and Sr(2+) (320 microM), but was only slightly increased by Ba(2+) (> 2 mM) and Co(2+) and not at all by Mg(2+). 4. The fast component, but not the slow component, was competitively blocked by Na(+) (median effective concentration, 44 mM) but not by Li(+), K(+) or Cs(+). Thus, the Ca(2+) sensor for the fast component of exocytosis is more selective than is that for the slow component; moreover, this selectivity appears to be based on ionic radius, with cations with radii of 0.84 to 1.13 A (1 A = 0.1 nm) being effective. 5. These data support a role for synaptotagmin--phospholipid as the Ca(2+) sensor for the exocytosis of large dense-core vesicles and they suggest that an additional Ca(2+)-sensing mechanism operates in the synchronous exocytosis of synaptic-like vesicles.

Animals↗
PubMed2001

Detection of Kaposi sarcoma-associated herpesvirus in bone marrow biopsy samples from patients with multiple myeloma.

BACKGROUND: Kaposi sarcoma-associated herpesvirus (KSHV) recently has been identified in the bone marrow (BM) dendritic cell of multiple myeloma (MM) patients. However, whether or not KSHV is associated with MM remains controversial because many studies have failed to detect the presence of KSHV DNA sequences in the BM of their MM patients. METHODS: We have assayed for KSHV DNA sequences in the BM biopsy samples from 49 patients with MM and from 8 patients with normal BM, using nested polymerase chain reaction and dot blot analysis. The polymerase chain reaction product of KSHV was further determined by single-strand conformation polymorphism and sequence analyses. RESULTS: KSHV DNA was detectable in 22 of 49 patients (44.9%) with MM but was not detectable in normal BM cells. Single-strand conformation polymorphism and sequence analyses showed that there were interpatient specific mutations. Sixteen out of 22 KSHV DNA sequences belonged to a previously defined subgroup, and the other 6 remain unclassified and may represent distinct strains of KSHV in Taiwan. CONCLUSIONS: Data strongly supported that KSHV infection did exist in the BM of the current study patients with MM. However, the role of KSHV in the pathogenesis of multiple myeloma remains to be determined.

Adult↗
PubMed2001

T(1) and T(2) selective method for improved SNR in CSF-attenuated imaging: T(2)-FLAIR.

We present here a method for improving SNR in CSF-attenuated imaging relative to the standard technique of using an inversion pulse and imaging at the null point of CSF. In this new method the inversion pulse is replaced with a 90(x)-180(y)-90(x) preparation sequence that provides T(1) and T(2) selectivity. This allows the tissue magnetization to recover more rapidly, allows for the use of shorter TR values, and reduces T(1) weighting. Magn Reson Med 45:529-532, 2001.

Blood Volume↗
PubMed2001

Nonlinear temporal dynamics of the cerebral blood flow response.

The linearity of the cerebral perfusion response relative to stimulus duration is an important consideration in the characterization of the relationship between regional cerebral blood flow (CBF), cerebral metabolism, and the blood oxygenation level dependent (BOLD) signal. It is also a critical component in the design and analysis of functional neuroimaging studies. To study the linearity of the CBF response to different duration stimuli, the perfusion response in primary motor and visual cortices was measured during stimulation using an arterial spin labeling technique with magnetic resonance imaging (MRI) that allows simultaneous measurement of CBF and BOLD changes. In each study, the perfusion response was measured for stimuli lasting 2, 6, and 18 sec. The CBF response was found in general to be nonlinearly related to stimulus duration, although the strength of nonlinearity varied between the motor and visual cortices. In contrast, the BOLD response was found to be strongly nonlinear in both regions studied, in agreement with previous findings. The observed nonlinearities are consistent with a model with a nonlinear step from stimulus to neural activity, a linear step from neural activity to CBF change, and a nonlinear step from CBF change to BOLD signal change.

Cerebrovascular Circulation↗
PubMed2001

Identification of three novel 6-pyruvoyl-tetrahydropterin synthase gene mutations (226C>T, IVS3+1G>A, 116-119delTGTT) in Chinese hyperphenylalaninemia caused by tetrahydrobiopterin synthesis deficiency.

The enzyme 6-Pyruvoyl-tetrahydropterin synthase (PTS) deficiency is the major cause of BH(4)-deficient HPA. The frequency of BH(4)-deficient HPA was estimated to be around 30% among Chinese HPA population in Taiwan, which is much higher than that in Caucasian population (1.5-2% of HPA). Approximately 86% of Chinese BH(4)-deficient HPA was found to be caused by PTS-deficiency. Seven mutations - namely R25G, N52S, V56M, V70D, P87S, D96N, and T106M - had been identified in Chinese PTS-deficient patients previously. In this study, five additional mutations in the PTS gene, namely 200C>T (T67M), 226C>T (L76F), IVS3+1G>A (K54X), 116-119delTGTT (K38X) and 169-171delGTG (V57del), were identified by PCR and DNA sequencing in Chinese PTS-deficient patients. The 116-119delTGTT introduces a frameshift stop after lysine of codon 38 (K38X). The G-to-A transition at the consensus sequence of splicing donor site of exon 3 (IVS3+1G>A) resulted in exon 3 skipping of the PTS transcript and caused a frameshift stop after lysine of codon 54 (K54X). The T67M and V57del mutations have been found in Caucasian PTS deficient patients, while the L76F, IVS3+1G>A, and K38X mutations are novel. None of 100 normal alleles screened was found to have the L76F substitution, which indicated that the L76F substitution is a mutation causing PTS deficiency. Hum Mutat 18:83, 2001.

Alleles↗
PubMed2001

Detection power, estimation efficiency, and predictability in event-related fMRI.

Experimental designs for event-related functional magnetic resonance imaging can be characterized by both their detection power, a measure of the ability to detect an activation, and their estimation efficiency, a measure of the ability to estimate the shape of the hemodynamic response. Randomized designs offer maximum estimation efficiency but poor detection power, while block designs offer good detection power at the cost of minimum estimation efficiency. Periodic single-trial designs are poor by both criteria. We present here a theoretical model of the relation between estimation efficiency and detection power and show that the observed trade-off between efficiency and power is fundamental. Using the model, we explore the properties of semirandom designs that offer intermediate trade-offs between efficiency and power. These designs can simultaneously achieve the estimation efficiency of randomized designs and the detection power of block designs at the cost of increasing the length of an experiment by less than a factor of 2. Experimental designs can also be characterized by their predictability, a measure of the ability to circumvent confounds such as habituation and anticipation. We examine the relation between detection power, estimation efficiency, and predictability and show that small increases in predictability can offer significant gains in detection power with only a minor decrease in estimation efficiency.

Artifacts↗
PubMed2001

Tetrahydrobiopterin-deficient hyperphenylalaninemia in the Chinese.

BACKGROUND: Hyperphenylalaninemia (HPA) may be caused by either a deficiency in phenylalanine-4-hydroxylase or in tetrahydrobiopterin (BH4), the essential cofactor required for the hydroxylation of aromatic amino acids. The most common forms of BH4 deficiency are 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency (MIM 261640) and dihydropteridine reductase (DHPR) deficiency (MIM 261630), which require a different treatment from classical HPA. RESULTS: Approximately 86% of BH4-deficient HPA in the Chinese population was found to be caused by PTPS deficiency. Eleven missense (73C-->G, 120T-->G, 155A-->G, 166G-->A, 200C-->T, 209T-->A, 226C-->T, 259C-->T, 286G-->A, 317C-->T, 430G-->C), one splicing (IVS3+1G-->A) and two deletion mutations (116-119delTGTT, 169-171delGTG) were identified in 37 unrelated PTPS-deficient Chinese families. Among these, 155A-->G, 259C-->T and 286G-->A mutation accounted for about 80% of the mutant alleles. The 155A-->G and 286G-->A mutations were found to be the common mutation in southern and northern Chinese, respectively. Only two Chinese DHPR-deficient families were detected among about 300 Chinese hyperphenylalaninemia cases. A single base transition 508G-->A on the DHPR cDNA was identified in two consanguineous DHPR-deficient siblings. A reduced level of DHPR mRNA expression was found in the other DHPR-deficient patient, which suggested that the mutation might lie in the regulatory region of the DHPR gene. CONCLUSIONS: The BH4-deficient HPA was estimated to make up around 30% of the Chinese population in Taiwan suffering from HPA, which is much higher than in Caucasian populations (1.5-2% of HPA).

5-Hydroxytryptophan↗
PubMed2000

Positive cooperativity without domains or subunits in a monomeric membrane channel.

The monomeric VDAC channel shows an accelerated pH titration of its transport properties with a Hill coefficient of about 2. This manifests itself as a sharp peak in conductance noise as well as a fast change in channel selectivity with pH. On the basis of the known structure of this channel, we propose that this cooperativity arises from a mechanically linked mobile pair of ionizable groups. Concerted movement of these groups between two states changes the distance from nearby electrostatic charge to influence the pK of the groups. This model of pH-dependent motion produces positive cooperative behavior that fits the observations without need for subunits or identifiable domains within the protein. The mathematical formalism has never required such domains, but these are generally considered an essential part of cooperative behavior in proteins. The present proposal reduces the size of a cooperative unit to a minimum, extending the limits of what is perceived to be possible. Together with large-scale conformational transitions, these subtle cooperative structural changes may allow proteins to adapt, with high sensitivity, to changes in their environment. They might also be relatively easy to engineer into a protein.

Allosteric Regulation↗
PubMed2000

Turbo ASL: arterial spin labeling with higher SNR and temporal resolution.

A modified pulsed arterial spin labeling (ASL) technique is introduced here that has both higher temporal resolution and higher SNR per unit time than existing ASL techniques. In this technique, the time TI between the application of the tag and image acquisition is longer than the repetition time TR, allowing for the use of greatly reduced TR values without a significant decrease in the amplitude of the ASL signal. This improves both the temporal resolution and the sensitivity of ASL for functional brain mapping.

Arteries↗
PubMed2000

Genetic analysis of growth inhibition of yeast cells caused by expression of Aspergillus oryzae RNase T1.

Even though most fungal hydrolytic enzymes have been successfully secreted in S. cerevisiae cells by expression of corresponding cDNA, overexpression of A. oryzae RNase T1 causes severe growth inhibition in yeast. We observed that yeast strains carrying RNase T1 cDNA under control of the GAL1 promoter with a single-copy vector were able to grow on galactose medium while those with a multi-copy vector were not. It was found that overexpression of three mutated versions of RNase T1 with low enzymatic activity did not affect the growth. We also observed that expression of RNase T1 without a signal sequence severely inhibited growth of the transformant even on the single-copy plasmid. Subcellular fractionation showed that overexpressed myc-tagged RNase T1 was localized in the membrane fraction. In the yeast secretory pathway, while the mutants defective in translocation into the ER, ER-Golgi trafficking and vacuole formation had severe growth inhibition during expression of RNase T1 from the single-copy plasmid. These results suggest that a mislocalization of active RNase T1 in cytosol by overflow from the secretory apparatus has toxic effects on the host cells.

Aspergillus oryzae↗
PubMed2000

Acute pancreatitis associated with temporal lobectomy and intractable seizure.

We present a rare case of acute pancreatitis associated with temporal lobectomy due to intractable seizure in a 23-year-old man. The patient underwent elective right temporal lobectomy and hippocampectomy. Severe upper abdominal pain occurred just 10 hours after surgery. The diagnosis of acute pancreatitis was based on the elevation of serum amylase and lipase levels, and the findings of abdominal computerized tomography. Other possible causative factors of acute pancreatitis including alcohol, biliary tract stone, hypertriglyceridemia, hypercalcemia, hyperparathyroidism, biliary dysmotility and autoimmune disease were excluded by a series of examinations. The possibility of drug-induced pancreatitis was very low in this patient. The patient was discharged after supportive treatment. No recurrence of seizure or abdominal pain was noted in the three months after discharge. Acute abdominal pain after brain surgery deserves clinical evaluation for acute pancreatitis.

Acute Disease↗
PubMed2000

Idiopathic myelofibrosis associated with renal extramedullary hematopoiesis and nephrotic syndrome: case report.

Idiopathic myelofibrosis is characterized by bone marrow fibrosis, anemia, leukoerythroblastosis, and extramedullary hematopoiesis in many organs. Renal abnormalities in idiopathic myelofibrosis have been rarely described in the literature and include extramedullary hematopoiesis in the pararenal or retroperitoneal areas resulting in obstructive uropathy and hemtopoietic cell infiltration in tubulointerstitial area and urolithiasis. These lead to azotemia or acute renal failure, which may respond well to radiotherapy and adjuvant chemotherapy. To our knowledge, there has been only one case report of nephrotic syndrome associated with glomerulonephritis in a myelofibrosis patient; however, no effective treatment was described. Herein, we report the case of a patient with idiopathic myelofibrosis who initially presented with hepatomegaly, anemia, and leukoerythroblastosis. A nephrotic syndrome developed 7 years after initial diagnosis. Renal biopsy disclosed the unique pathological finding of simultaneous mesangial proliferative glomerulonephritis, renal extramedullary hematopoiesis, and gouty nephropathy. Despite treatment with busulfan, proteinuria persisted that implied irreversible glomerular injury and a terminal prognosis. We focus on the unusual pathological finding and the association between nephrotic syndrome and idiopathic myelofibrosis.

Aged↗
PubMed1999

Multiple and diverse forms of regulated exocytosis in wild-type and defective PC12 cells.

Regulated exocytosis triggered by the photolysis of a caged Ca2+ compound, DM-nitrophen, was investigated by patch-clamp capacitance measurements in two clones of PC12, the first wild-type and the second (PC12-27) defective of both types of classical secretory vesicles together with the neuronal-type receptors for the attachment proteins of the N-ethylmaleimide-sensitive fusion protein, the so called SNAREs. Moreover, the electrophysiological data were correlated with the ultrastructure of resting quick-frozen-freeze-dried cells of the two clones. Wild-type PC12 exhibited two-component capacitance responses, time constants of 30-100 ms and >10 s, that previous studies had suggested to reflect primarily the fusion of the small and large secretory vesicles, each contributing cell surface increases of approximately 10%. Both of these components were largely and specifically inhibited whether cells previously were microinjected with tetanus toxin light chain. In the defective clone, large responses also were recorded ( approximately 19% surface expansion; time constant, approximately 1 s) that, in contrast to those of the wild-type, were entirely resistant to the toxin. Although secretory organelles, i.e., large vesicles and also profiles of small vesicles, were abundant at the cell periphery and often docked to the plasmalemma of resting wild-type PC12, in the defective clone, no superficial accumulation of vesicles was observed. Our coordinate structural and functional results have revealed diversities between the two classical forms of regulated secretion in wild-type PC12 and have provided evidence of a toxin-insensitive form of Ca2+-induced exocytosis, prominent in the defective clone, that may play an important role(s) in cellular physiology.

Acetates↗