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Biomedical subjects

C L Chou

Publications and source records attributed to C L Chou.

At least 55 records · Page 3Linked to original sources
PubMed1993

A common sequence motif near nonhomologous recombination breakpoints involving Ig sequences.

Analysis of nonhomologous recombination events at the Ig loci revealed that a four base sequence, 5'-CCAG-3', or its complement, 5'-CTGG-3', is present within seven nucleotides in 12 of the 13 examined recombination breakpoints. Statistical analysis of the data indicates that this occurrence has a probability of less than 10(-5) of occurring by chance. This sequence is infrequently found at nonhomologous recombination breakpoints in non-Ig sequences, suggesting that its contribution may be either Ig- or B cell-specific. Intriguingly, this tetranucleotide is also found to be associated with the breakpoints of VH gene replacement and isotype switching, suggesting that common pathways may be involved in all three B cell processes.

B-Lymphocytes↗
PubMed1993

An insertion-deletion event in murine immunoglobulin kappa gene resembles mutations at heavy-chain disease loci.

The analysis of spontaneous somatic mutants gives insights into the regulation of gene expression. Human heavy-chain disease (HCD) is a monoclonal lymphoproliferative disorder characterized by the presence of truncated immunoglobulin (Ig) heavy chains without associated light chains. To better understand the molecular mechanisms leading to the loss of light-chain production, we have examined a murine cell line model of heavy-chain disease. R15, a spontaneous mutant of the IgA, kappa-producing myeloma cell line W3129, produces heavy chain but no light chain. The variant delta 15 derived from R15 resembles human HCD in that it secretes a shortened heavy chain with no associated light chain. Cloning and analysis of the R15 kappa light-chain gene revealed that a 358-nucleotide insertion of unknown origin replaced 22 bases of the wild-type leader-variable region (L-V) intron (IVS). Although this genomic change left the light-chain exons and known regulatory elements intact, it altered the mRNA processing pathway, yielding two alternative RNA products, neither of which encodes a functional protein. This mutant therefore provides new insights into how genomic changes can influence gene expression.

Animals↗
PubMed1993

In vitro perfusion of chinchilla thin limb segments: urea and NaCl permeabilities.

We measured the urea and NaCl permeabilities (Purea and PNaCl, respectively) of the following nephron segments from chinchilla: the upper part of the long-loop descending limb (from outer medulla, LDLu), the middle part of the long-loop descending limb (from outer 30% of the inner medulla, LDLm), the lower part of the long-loop descending limb (from deep inner medulla, LDLl), and the thin ascending limb (from deep inner medulla, ATL). We found that Purea (x10(-5) cm/s) was relatively low in the LDLu (3.3), but that the value was larger in the inner medullary thin descending limb (16.8 for LDLm and 47.6 for LDLl). The ATL had an even higher value (170). Phloretin, 0.25 mM, added to the peritubular bath had no effect on Purea of these segments, suggesting that the rapid transport rate is not due to a phloretin-sensitive facilitated transport pathway like that seen in the inner medullary collecting duct. PNaCl (x10(-5) cm/s) also increased with distance along the length of the thin descending limb (LDLu, 11.7; LDLm, 41.2; LDLl, 98.4; and ATL, 321). Calculations from NaCl dilution potential measurements showed that LDLu was Na+ permselective, whereas LDLl and ATL were Cl- permselective. High solute permeabilities in the inner medullary thin descending limb contradict a major requirement of the passive model of urinary concentration developed previously (J. P. Kokko and F. C. Rector, Jr. Kidney Int. 2: 214-223, 1972; and J. L. Stephenson. Kidney Int. 2: 85-94, 1972).

Animals↗
PubMed1993

Structural-functional correlation in chinchilla long loop of Henle thin limbs: a novel papillary subsegment.

The ultrastructural characteristics of thin limb subsegments from chinchilla long loops of Henle were studied in perfusion-fixed kidneys and in isolated perfused tubules. In sections from the perfusion-fixed kidneys, we noted types I, II, III, and IV thin limb epithelia similar to those previously identified in other rodent species. Sections from the deepest 20% of the papillary tip, however, revealed only a single thin limb epithelial type, which had a combination of structural characteristics distinct from previously identified thin limb subtypes. This "papillary type" epithelium had relatively tall cells and a complex cellular organization with extensive interdigitation, numerous shallow tight junctions, and microvilli. In single-tubule studies, thin limb segments dissected from different levels of the outer and inner medulla were perfused in vitro for osmotic water permeability (Pf) measurements and were fixed for ultrastructural examination. Long-loop thin descending limbs (LDL) dissected from the outer medulla (Pf, 2,637 +/- 336 micron/s) had type II epithelium. LDL dissected from the middle of the inner medulla (Pf, 1,570 +/- 76 microns/s) had a type III epithelium. LDL segments dissected from the deepest 20% of the inner medulla had a low but nonzero Pf (68 +/- 9 micron/s) and had the same novel papillary type epithelium seen in sections from fixed kidneys. Thin ascending limbs dissected from inner 50% of the inner medulla had essentially zero Pf (8 +/- 4 micron/s) and had a type IV epithelium. Immunohistochemical localization of CHIP28 water channel protein confirmed the presence of CHIP28 in thin descending limbs throughout the outer 75% of the inner medulla, whereas labeling was essentially absent in the deep inner medulla where the low-PfLDL (novel papillary type epithelium) is located.

Animals↗
PubMed1992

Kinetics of urea and water permeability activation by vasopressin in rat terminal IMCD.

The vasopressin-regulated urea carrier and the vasopressin-regulated water channel are distinct transporters present in the apical membrane of the inner medullary collecting duct (IMCD) cells. To assess whether these transporters may be activated by common mechanisms, we investigated the time course of increase of urea and water permeability in response to vasopressin in isolated perfused terminal IMCD segments. The permeability responses were determined through the use of a specially designed continuous-flow fluorometer for rapid analysis of collected tubule fluid samples. The time courses of activation of the two transporters by vasopressin were virtually identical. Both urea and water permeability displayed a rapid initial increase for the first 10 min followed by a slower secondary response lasting at least 30 additional min. The lag periods between vasopressin addition and the initial rise in permeability were the same for urea (34.2 +/- 8.8 s) and water (34.8 +/- 8.9 s) transport activation. Furthermore, the initial rate of permeability increase (normalized by the total increase) was not significantly different for the two transport processes. The lag periods for the increase in urea permeability in response to 8-bromoadenosine 3',5'-cyclic monophosphate and vasopressin were not significantly different. The results are consistent with the view that the rate-limiting step in vasopressin-induced activation is the same for both the urea carrier and water channel and may lie at a step beyond generation of adenosine 3',5'-cyclic monophosphate.

Animals↗
PubMed1992

In vitro perfusion of chinchilla thin limb segments: segmentation and osmotic water permeability.

The thin limb segments of the long loop of Henle are thought to play important roles in the urinary concentrating mechanism. In this study, we present new approaches to the identification, dissection, and in vitro perfusion of individual thin limb segments from all levels of the chinchilla renal medulla, including the deepest portions of the papilla. We have applied these techniques to the investigation of the osmotic water permeability along the chinchilla long loop of Henle. The results demonstrate that the osmotic water permeability of the thin descending limb is not uniformly high along its length, as previously thought, but that the distal 20% of the long-loop descending limb has a very low water permeability (approximately 50 microns/s). The transition to the low water permeability region of the thin descending limb is accompanied by a relatively abrupt change in morphology (increased cellularity and decreased diameter) that is readily perceptible in the perfused segments and even in the dissection dish. In contrast, the upper part of the chinchilla long-loop thin descending limb had an extremely high osmotic water permeability (greater than 2,000 microns/s) as observed in other species. Thin ascending limbs from deep in the inner medulla had water permeabilities that were indistinguishable from zero, as previously found in thin ascending limbs from near the inner-outer medullary junction. The presence of a low-water-permeability portion of the long-loop thin descending limb in chinchilla may have important implications with regard to the inner medullary concentrating process. A relatively low osmotic water permeability (397 microns/s) was also found in the deep inner medullary portion of the thin descending limb from the rat.

Animals↗
PubMed1992

Terbutaline acts at multiple sites to inhibit bronchoconstriction induced by dry air in canine peripheral airways.

We examined the effect of the beta 2-agonist terbutaline on dry airflow-induced bronchoconstriction (AIB) in the canine lung periphery. Using a wedged bronchoscope technique, collateral resistance (Rcs) and airway wall temperature (Taw) were measured before and after a 2-min exposure to dry air. When sublobar segments were challenged with dry air, Taw fell during challenge (p less than 0.001), and Rcs increased 5 min postchallenge (p less than 0.01). Pretreatment with terbutaline (100 micrograms/kg) reduced the fall induced by dry-air challenge in Taw by 37% and the subsequent rise in Rcs by 87%. Terbutaline significantly reduced the concentrations of thromboxane B2 (TxB2) and prostaglandin D2 (PGD2), and decreased the concentration of epithelial cells recovered in bronchoalveolar lavage fluid 5 min postchallenge. In addition, terbutaline attenuated histamine- and PGD2-induced constriction. Finally, peripheral lung sensitivity (as assessed by delta Rcs/delta Taw) to challenge after treatment with terbutaline was significantly less than that calculated for untreated control animals (p less than 0.05). These data are consistent with the idea that terbutaline attenuates AIB by (1) facilitating replacement of water lost during exposure to dry air, (2) inhibiting mediator production and release from osmosensitive cells, and (3) reducing smooth muscle responsiveness.

Airway Resistance↗
PubMed1992

Experimental tests of three-dimensional model of urinary concentrating mechanism.

Recently, a new model of the urinary concentrating process has been proposed that takes into account the three-dimensional architecture of the renal medulla. Under the assumptions of the model, computer simulations predicted significant axial osmolality gradients in the inner medulla without active transport by the inner medullary loop of Henle. Two of the model assumptions (which constitute hypotheses for this study) were: (1) the osmotic water permeability of the initial part of the inner medullary collecting duct (initial IMCD) is very low even in the presence of vasopressin; and (2) there is significant lateral separation of structures such that thin descending limbs are far from the collecting ducts at the same inner medullary level. The first hypothesis was addressed by perfusing rat initial IMCD segments in vitro and measuring osmotic water permeability. With the osmotic gradient oriented as predicted by the model (lumen greater than bath), vasopressin increased the osmotic water permeability from 286 to 852 microns/s. Three additional series of experiments confirmed the high water permeability in the presence of vasopressin. The second hypothesis was addressed by morphometric analysis of histologic cross-sections of the rat renal medulla. Mean distances of descending limbs to the nearest adjacent collecting duct were very small throughout the inner medulla (less than 6 microns) and substantially less than in the outer medulla (28 microns). It was concluded that the data are inconsistent with both hypotheses and therefore do not support the feasibility of the "three-dimensional" model of the renal inner medulla. The axial distributions of loops of Henle and collecting ducts in the rat renal medulla are also reported.

Animals↗
PubMed1991

Isolation and characterization of metal-binding proteins (metallothioneins) from lobster digestive gland (Homarus americanus).

Two metallothionein (low-molecular-weight, metal-binding proteins) preparations, MT-1 and MT-2, have been isolated from the digestive gland of American lobster (Homarus americanus) contaminated with Cd. MT-1 contains Cd- and Cu-binding proteins, whereas MT-2 is a reasonably pure Cd-binding protein. The properties of MT-1 and MT-2 with respect to amino acid and elemental compositions, heat stabilities, polarographic, high-performance liquid chromatography (HPLC), and isoelectric focussing behaviors are reported. Lobster metallothioneins share a number of similarities with mammalian metallothioneins with respect to the presence of Cd and Cu, apparent molecular weights, amino acid compositions, UV absorption spectra at various pH, and polarographic behavior, but differ substantially in their electrophoretic behavior.

Amino Acids↗
PubMed1991

The reactivity of EDTA, copper ion, and copper citrate with metallothioneins isolated from the digestive gland of cadmium-contaminated lobster (Homarus americanus).

The reactivity of EDTA, Cu2+, and copper citrate with two metallothionein preparations (MT-1 and MT-2) isolated from the digestive gland of Cd-contaminated American lobster (Homarus americanus) was studied. Under pseudo-first-order conditions, metallothioneins reacted with EDTA for removal of Cd2+ in a multiphasic manner. Cadmium(+II) removal by Cu2+ was complex and non-stoichiometric, suggesting different binding sites. Rabbit liver metallothionein reacted similarly. Cadmium removal from lobster metallothionein by copper citrate was slow and triphasic in nature. EDTA removed Cu2+ from lobster metallothionein very slowly.

Animals↗
PubMed1991

Regulation of collecting duct water permeability independent of cAMP-mediated AVP response.

We have used the isolated perfused tubule technique, measurements of adenosine 3',5'-cyclic monophosphate (cAMP) content in single tubules, and freeze-fracture electron microscopy to study the basis of high vasopressin-independent (basal) osmotic water permeability (Pf) in the terminal inner medullary collecting duct (IMCD) of the rat. The results confirmed the observation that the basal Pf of the terminal IMCD is considerably higher than that of the initial IMCD. They also showed that the basal Pf of the terminal IMCD is regulated by in vivo factors related to water intake, such that a very high vasopressin-independent Pf can be induced in isolated tubules by prior in vivo thirsting. Tubules from thirsted rats did not display elevated urea permeabilities, nor did they exhibit measurable cAMP levels in the absence of exogenous vasopressin, indicating that the high basal Pf was not due to residual binding of vasopressin to its receptors. Freeze-fracture studies in thirsted rats demonstrated the presence of intramembrane particle (IMP) clusters in both initial and terminal IMCD, with more in the latter. Water loading of the rats suppressed the incidence of clusters almost entirely but did not fully suppress the basal Pf in the terminal IMCD, raising the possibility that a component of transepithelial water transport may occur independently of the vasopressin-regulated IMP clusters. On the basis of these results, we conclude that the vasopressin-independent Pf in the terminal IMCD can be stably elevated to very high levels in response to in vivo thirsting. This elevation appears to be due to a chronic conditioning effect mediated by unknown in vivo factors and is not due to the short-term cAMP-mediated regulatory effect of vasopressin.

Animals↗
PubMed1991

Cyclooxygenase pathway mediates lung injury induced by phorbol and platelets.

The role of platelets in lung injury has not been well defined. In the present study of isolated perfused rat lungs, phorbol myristate acetate (PMA; 0.15 microgram/ml) or platelets (6.7 X 10(4)/ml) alone did not discernibly change the pulmonary arterial pressure (PAP) or lung weight (LW). However, the combination of platelets and PMA drastically increased the PAP and LW (delta PAP 26.2 +/- 1.0 mmHg, delta LW 2.7 +/- 0.4 g). delta PAP was positively correlated with the increase in thromboxane B2 produced by infusion of platelets and PMA (thromboxane B2 = 35.6 + 0.97 delta PAP, r = 0.67, P less than 0.01). The hypertension and edema formation induced by PMA and platelets were strongly attenuated by indomethacin, an inhibitor of platelet cyclooxygenase (delta PAP 5.6 +/- 2.0 mmHg, P less than 0.001; delta LW 0.0 +/- 0.1 g, P less than 0.001), and by imidazole, an inhibitor of thromboxane A2 synthase (PAP 8.0 +/- 2.5 mmHg, P less than 0.001; LW 0.0 +/- 0.3 g, P less than 0.01). Inactivation of platelet lipoxygenase with nordihydroguaiaretic acid mildly depressed pulmonary pressure but did not affect delta LW (delta PAP 18.9 +/- 1.6 mmHg, P less than 0.05; delta LW 3.1 +/- 0.3 g, P greater than 0.05). In vitro experiments showed that the capacity of platelets to release oxygen radicals was only 2.6% of that found for granulocytes. These results suggest that platelets may be activated by PMA to increase PAP and vascular permeability.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

[Median nerve lesions at wrist in cyclists].

The purpose of this study is to detect the median nerve lesions at wrist in professional cyclists. Totally 14 national representative cyclists were included. Each subject was questionnaired and asked to draw their site of hand discomfort, followed by hand grip power test with grasp, lateral pinch and palmar pinch. A control group of 30 medical students were also tested for grip power. Electrodiagnostic examination of bilateral median nerves was then done on every cyclist, including motor and sensory nerve conduction studies, and needle EMG on abductor pollicis brevis and other associated muscles. Of the 28 hands in 14 cyclists, 7 in 4 subjects had neurologic symptoms related to median nerve, and 5 in 4 subjects had abnormal electrodiagnostic examinations. The grip power was significantly better in cyclists than in control. The prevalence of median nerve lesions at wrist in cyclists, although usually mild, was substantially higher than expected. Electrodiagnosis can be used as a sensitive detector for neuropathy even at subclinical stage. It is suggested that cyclists and trainers should be aware of the median nerve lesion during cycling and training in order to take early preventive, diagnostic and therapeutic procedures.

Adolescent↗