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Biomedical subjects

M B Wang

Publications and source records attributed to M B Wang.

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

Decreased electromechanical activity of guinea pig circular muscle during pregnancy.

BACKGROUND: Delayed gastric emptying has been reported during pregnancy; however, its underlying mechanism is poorly understood. The purpose of this study was to determine if electromechanical activity of antral circular muscle is decreased during pregnancy. METHODS: Antral muscle strips from third-trimester pregnant and age-matched control virgin female guinea pigs were studied in vitro. RESULTS: Spontaneous and bethanechol-induced phasic antral contractions from pregnant guinea pigs were reduced significantly in force compared with control virgin animals. Although the resting membrane potentials were similar, the electric slow waves of pregnant animals displayed significant decreases in upstroke amplitude, plateau amplitude, and number of spikes during the plateau potential compared with control animals. The voltage-tension relationship was similar in pregnant and control animals. CONCLUSIONS: This study indicates that (1) the force of antral circular muscle contractions is decreased during pregnancy and (2) this decreased force is secondary to a diminished slow wave depolarization. The results suggest that a change in electromechanical activity of gastric muscle is a cause of altered gastric motility in pregnancy.

Animals↗
PubMed1992

Extranodal American Burkitt's lymphoma of the head and neck.

Burkitt's lymphoma was first described in 1958 as a mandibular malignancy found in African children. The American, or nonendemic, form of the disease differs from the African form in that the tumor most often presents with abdominal or bone marrow involvement. Head and neck manifestations of American Burkitt's lymphoma are encountered in less than a quarter of the reported cases and usually present as cervical adenopathy. A review of all cases of American Burkitt's lymphoma treated at the UCLA Medical Center, Los Angeles, Calif, from 1971 to 1989 revealed an unusual subset of seven patients with American Burkitt's lymphoma of the head and neck who presented with extranodal disease of the soft tissues or bones of the face. The medical literature was reviewed to compile similar cases of extranodal American Burkitt's lymphoma. The clinical and pathologic features of these cases, their radiographic findings, and treatment are described.

Adult↗
PubMed1992

A complete sequence of the rice sucrose synthase-1 (RSs1) gene.

Using a fragment of the maize sucrose synthase gene Sh-1 as probe, the rice genome was shown to contain at least three genes encoding sucrose synthase. One of these genes was isolated from a genomic library, and its full sequence, including 1.7 kb of 5' flanking sequence and 0.9 kb of 3' flanking sequence, is reported. The new rice gene, designated RSs1, is highly homologous to maize Sh-1 (approx. 94% identity in derived amino acid sequence), and contains an identical intron-exon structure (16 exons and 15 introns). Both RSs1 and maize Sh-1 show similar sequence homologies to a second rice sucrose synthase gene described recently (designated RSs2, Yu et al. (1992) Plant Mol Biol 18: 139-142), although both the rice genes predict an extra 6 amino acids at the C-terminus of the protein when compared to the maize gene. The RSs1 5' flanking sequence contains a number of promoter-like sequences, including putative protein-binding regions similar to maize zein genes.

Amino Acid Sequence↗
PubMed1992

Modulation of cat antral slow waves by ion substitution, Ca2+ and K+ channel blockade, and ACh stimulation.

Two distinct slow waves can be recorded from smooth muscle cells on the submucosal border (submucosal cells) and the myenteric border (myenteric cells) in the circular layer of the cat antrum. The present studies examined the effects of decreasing extracellular Na+ ([Na+]o) or Ca2+ concentration ([Ca2+]o), Ca2+ and K+ channel blockade, and acetylcholine (ACh) stimulation on "submucosal" and "myenteric" slow waves using intracellular recording techniques. Decreasing [Na+]o (30 mM) reduced the upstroke depolarization of slow waves from submucosal cells but had no effect on the upstroke depolarization of myenteric cells. Decreasing [Ca2+]o (0.5 mM) decreased the upstroke depolarization in cells from each area. Neither cadmium (200 microM) nor nifedipine (100 microM) had any effect on the upstroke depolarizations from both submucosal and myenteric slow waves. In contrast, nickel (5 mM), a nonselective Ca2+ channel blocker, decreased the upstroke depolarizations of slow waves from submucosal and myenteric cells. Slow waves from myenteric cells normally exhibit a plateau phase of several seconds duration. The amplitude of the plateau potential could be decreased by lowering [Na+]o or [Ca2+]o or by nickel, cadmium or nifedipine. In the presence of 30 mM Na+ slow waves from submucosal cells appeared to develop plateau potentials. K+ channel blockade with tetrabutylammonium (TBA, 5 mM) or cesium (10 mM) increased the upstroke depolarization and delayed membrane repolarization in slow waves from submucosal cells. TBA and cesium also increased the upstroke depolarization from myenteric cells but did not delay membrane repolarization. ACh (1 and 3 microM) caused the generation of plateau potentials in slow waves from submucosal cells and increased slow-wave duration.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1991

Effect of muscle length on isometric stress and myosin light chain phosphorylation in gallbladder smooth muscle.

These experiments were designed to characterize the effect of muscle length on isometric stress, sensitivity to stimulation, and phosphorylation of the 20,000-Da myosin light chains in guinea pig gallbladder smooth muscle. Basal, active, and total isometric stress were determined in acetylcholine- or K(+)-treated (10(-4) M ACh, 80 mM KCl) muscle strips at 0.6-1.3 times the optimal muscle length (Lo) for isometric stress development. The effect of muscle length on the sensitivity to ACh and K+ was determined in cumulative dose-response experiments (10(-8) to 10(-4) M ACh, 10-80 mM KCl) at 0.7, 1.0, and 1.3 Lo. The effect of muscle length on myosin light chain phosphorylation was determined in ACh- or K(+)-treated (10(-4) M ACh, 80 mM KCl) muscle strips at 0.7, 1.0, and 1.3 Lo. In gallbladder smooth muscle, 1) active isometric stresses at 0.7 and 1.3 Lo were less than active isometric stress at 1.0 Lo; 2) the sensitivity of developed stress was similar at 1.0 and 1.3 Lo but decreased at 0.7 Lo; 3) the decline in isometric stress and sensitivity at 0.7 Lo was associated with reduced levels of phosphorylated myosin light chain; and 4) the decline in isometric stress at 1.3 Lo was not associated with reduced amounts of phosphorylated myosin light chain. These results suggest that the decline in active stress and sensitivity at short muscle lengths (L less than Lo) in gallbladder smooth muscle is due, at least in part, to decreases in the activation of the myofilaments. The decline in active isometric stress at long muscle lengths (L greater than Lo) is not due to changes in myofilament activation.

Acetylcholine↗
PubMed1991

Electrical slow-wave activity from the circular layer of cat terminal antrum.

Intracellular recording techniques were used to characterize the electrical slow-wave activity through the thickness of the circular muscle layer of the cat terminal antrum. Muscle strips were pinned out in cross section to the floor of a recording chamber perfused with Krebs buffer. Circular muscle cells from the myenteric to the submucosal border then were impaled with 20- to 40-M omega glass microelectrodes, and slow-wave activity was recorded. Slow waves from the myenteric side of the circular layer consisted of an upstroke depolarization, a prominent plateau phase, and a downstroke repolarization. Slow-wave characteristics for cells along the myenteric border were Em, -74.2 +/- 1.3 mV; duration, 5.3 +/- 0.5 s; upstroke amplitude, 29.4 +/- 3.4 mV; upstroke velocity, 0.20 +/- 0.03 V/s; and frequency, 5.8 +/- 0.5/min. Slow waves from muscle cells along the submucosal side of the preparation lacked a discernible plateau phase. Slow waves from submucosal border cells had the following characteristics: Em, -80.4 +/- 1.4 mV (P less than 0.01); duration, 3.5 +/- 0.4 s (P less than 0.01); upstroke amplitude, 44.0 +/- 2.4 mV (P less than 0.01); upstroke velocity, 0.56 +/- 0.06 V/s (P less than 0.01); and frequency, 4.2 +/- 0.4/min (P less than 0.05). Slow waves were not affected by 10(-7)M tetrodotoxin and 10(-6)M atropine or by removal of the longitudinal muscle layer. Slow-wave activity within each region was maintained after dissecting the circular layer into submucosal and myenteric segments. The results suggest that two distinct slow waves exist within the circular muscle layer of the cat terminal antrum.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Myosin light chain phosphorylation and contraction of guinea pig gallbladder smooth muscle.

These experiments were designed to determine 1) whether acetylcholine (ACh) stimulation is accompanied by changes in myosin light chain phosphorylation in gallbladder smooth muscle and 2) whether dephosphorylated noncycling cross bridges (latch bridges) exist in gallbladder smooth muscle. Isometric stress, isotonic shortening velocity, and myosin light chain phosphorylation were determined under conditions of contraction and relaxation in ACh-stimulated guinea pig gallbladder smooth muscle. Unstimulated muscle contained 6.8 +/- 2.0% phosphorylated myosin light chain. ACh stimulation (5 x 10(-5) or 10(-4) M) was associated with a rapid increase in myosin light chain phosphorylation to a value that was maintained throughout the tonic contraction. In contrast, isotonic shortening velocity was maximal at 30 s of stimulation and then declined over time to a steady-state level that was 25-30% of the peak velocity. Upon agonist washout (relaxation), dephosphorylation of the myosin light chain occurred at about the same rate as the decline in shortening velocity and preceded the decline in isometric stress. These data suggest that ACh stimulation is accompanied by changes in myosin light chain phosphorylation but that dephosphorylation of cross bridges is not necessary for the slowing of cross-bridge cycling rates in gallbladder smooth muscle.

Acetylcholine↗
PubMed1991

Skull base malignancy following long-term sinus mucocele and osteomyelitis.

A case of skull base malignancy following long-term sinus mucocele is presented. While the similarity in clinical signs between sinus mucocele and malignancy has recently been emphasized in the literature, no previous case of skull base malignancy following frontoethmoid mucocele has been reported. The literature is reviewed and the association between inflammatory conditions and sinus malignancy is outlined.

Adult↗
PubMed1991

Hierarchical immunosuppression of regional lymph nodes in patients with head and neck squamous cell carcinoma.

Patients with head and neck squamous cell carcinomas (HNSCCs) manifest defects in cell-mediated immune function. Previous studies in this laboratory have demonstrated regional alterations in the immunocompetence of draining lymph nodes (LNs) in HNSCC patients. In this investigation, we studied functional activity of lymphocytes from lymph nodes in different locations in the radical neck dissections (RNDs) from patients undergoing operations for HNSCC. Lymphocytes from nodes close to the primary tumor ("near" lymph nodes or NLN) exhibited a significant decrease in interleukin-2 (IL-2)-activated cytotoxicity when compared to lymphocyts from distant nodes ("far" lymph nodes or FLN). In addition, co-culture experiments suggested the existence of a soluble regulatory factor, produced by lymph nodes, that inhibited the development of lymphokine-activated killer (LAK) cells in vitro. Further experiments with conditioned supernatants from the lymph node cells confirmed the presence of this soluble inhibitory factor. The inhibitory effect is significantly greater in NLNs than in FLNS. This hierarchical phenomenon suggests a regional network of immunosuppression in HNSCC patients. It is likely that tumor- and lymph node-induced suppression plays a role in limiting the efficacy of current immunotherapy protocols in human beings. A greater understanding of mechanisms of local inhibition of immune function will aid in improving adoptive immunotherapy for treatment of cancers in human beings.

Aged↗
PubMed1990

Contribution of intracellular calcium to gallbladder smooth muscle contraction.

Studies were performed to evaluate the contribution of intracellular Ca2+ to gallbladder smooth muscle contraction under acetylcholine (ACh) or potassium stimulation. Gallbladder smooth muscle strips from adult guinea pigs were placed in tissue baths containing N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES)-buffered physiological salt solution (PSS) and set to optimal length for contraction (Lo). The results were as follows, 1) A 20-min equilibration in zero Ca2(+)-0.1 mM ethylene glycol-bis( beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) PSS virtually abolished the response to potassium but not to ACh. 2) Substitution of strontium, an inhibitor of intracellular Ca2+ release, for Ca2+ significantly decreased the contractile response to ACh (3 X 10(-5), 10(-4), and 3 X 10(-4) M). Strontium had no effect on the response to 40 and 80 mM potassium. 3) Intracellular Ca2+ depletion significantly decreased gallbladder smooth muscle contraction to ACh (10(-4) M) but had no effect on the response to potassium (80 mM). 4) Ryanodine, a compound that inhibits Ca2+ storage by the sarcoplasmic reticulum, significantly decreased the contractile response to ACh (10(-4) M) but not to potassium (80 mM). These data support the observation that the use of intracellular Ca2+ by gallbladder smooth muscle for contraction is agonist dependent.

Acetylcholine↗
PubMed1990

Efficacy and morbidity of partial laryngectomy and postoperative radiation therapy.

In recent years, we have seen increasing use of partial laryngectomies for larger lesions that were previously treated by total laryngectomy. The resultant closer margins have made postoperative radiation therapy an important adjuvant treatment to conservation laryngeal surgery. We review the University of California, Los Angeles, experience with combination partial laryngectomy and postoperative radiation therapy between 1973 and 1987 for treatment of carcinoma of the larynx. Twenty-four such patients who underwent partial laryngectomies and postoperative radiation therapy are examined. Techniques of treatment, complications, and the functional ability of the remaining larynx are discussed. The locoregional control rate at 5 years was 80%. Risk factors associated with an increased risk of recurrence were positive margins, vascular invasion, and extranodal spread. There were no major problems with postoperative wound healing or airway management during the radiation treatment. Vocal and swallowing function were well preserved in most cases. We conclude that combination partial laryngectomy and radiation therapy permits preservation of laryngeal function without serious complications, and therefore is an effective treatment for selected patients with carcinoma of the larynx.

Adult↗
PubMed1987

Effect of pregnancy on gastric motility in vivo and in vitro in the guinea pig.

Experiments were designed to examine the effects of pregnancy on gastric emptying and on the in vitro contractile response of gastric smooth muscle to cholinergic stimulation. Gastric emptying of a radio-labeled liquid marker (51Cr in saline) was determined at regular intervals (5, 15, 30, and 60 min) in nonpregnant and pregnant (third trimester) guinea pigs. Gastric emptying after 30 min also was determined for animals 1 and 4 days postpartum. The in vitro contractile responses of muscle strips from the fundus, corpus, and antrum of nonpregnant and pregnant animals after stimulation with acetylcholine were analyzed with respect to the maximal force developed and the pD2 value (negative logarithm of the dose that gives a one-half maximal response). The results can be summarized as follows. Pregnancy was characterized by an increase in the amount of marker retained within the stomach at each time point. For nonpregnant animals the time to one-half emptying was approximately 10 min; in pregnant animals this was prolonged to 30 min. Gastric emptying was reduced in animals 1-day postpartum but returned to normal by 4 days after delivery. In contrast, pregnancy had no effect on the maximal contractile response to acetylcholine of muscle strips from the orad and caudad stomach or on their respective pD2 values. The results suggest that pregnancy is associated with decreased gastric emptying of liquids in the guinea pig, but that the delay cannot be attributed to alterations in the maximal force-generating capacity of gastric smooth muscle.

Acetylcholine↗