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Biomedical subjects

H S Hall

Publications and source records attributed to H S Hall.

9 recordsLinked to original sources
PubMed2000

A novel membrane-anchored Rab5 interacting protein required for homotypic endosome fusion.

The ras-related GTPase rab5 is rate-limiting for homotypic early endosome fusion. We used a yeast two-hybrid screen to identify a rab5 interacting protein, rab5ip. The cDNA sequence encodes a ubiquitous 75-kDa protein with an N-terminal transmembrane domain (TM), a central coiled-coil structure, and a C-terminal region homologous to several centrosome-associated proteins. rab5ip lacking the transmembrane domain (rab5ipTM(-)) had a greater affinity in vitro for rab5-guanosine 5'-O-2-(thio)diphosphate than for rab5-guanosine 5'-3-O-(thio)triphosphate. In transfected HeLa cells, rab5ipTM(-) was partly cytosolic and localized (by immunofluorescence) with a rab5 mutant believed to be in a GDP conformation (GFP-rab5(G78A)) but not with GFP-rab5(Q79L), a GTPase-deficient mutant. rab5ip with the transmembrane domain (rab5ipTM(+)) was completely associated with the particulate fraction and localized extensively with GFP-rab5(wt) in punctate endosome-like structures. Overexpression of rab5ipTM(+) using Sindbis virus stimulated the accumulation of fluid-phase horseradish peroxidase by BHK-21 cells, and homotypic endosome fusion in vitro was inhibited by antibody against rab5ip. rab5ipTM(-) inhibited rab5(wt)-stimulated endosome fusion but did not inhibit fusion stimulated by rab5(Q79L). rab5ip represents a novel rab5 interacting protein that may function on endocytic vesicles as a receptor for rab5-GDP and participate in the activation of rab5.

Amino Acid Sequence↗
PubMed1999

Specific changes in beta2-adrenoceptor trafficking kinetics and intracellular sorting during downregulation.

Agonist-activated beta2-adrenoceptors rapidly internalize and then recycle to the cell surface, however chronic agonist eventually causes receptor downregulation. To characterize beta2-adrenoceptor trafficking kinetics and intracellular sorting during downregulation, human embryonic kidney cells expressing epitope-tagged receptors were examined by radioligand binding with (+/-)-[3H]4-(3-tertiarybutylamino-2-hydroxypropoxy)-benzimidazole- 2-on hydrochloride ([3H]CGP12177) and immunofluorescence microscopy. The first-order receptor recycling rate constant declined after 18 h of agonist compared with 15 min (0.05 min(-1) vs. 0.12 min(-1)), thus increasing the intracellular transit time (20.0 min vs. 8.3 min). There was also a reduction in the rate of receptor endocytosis and a decline in the total number of receptors. Although the intracellular receptor fraction did not increase between 15 min and 18 h of agonist, some receptors moved irreversibly into a protease-containing compartment while retaining radioligand binding activity. Our results indicate that beta2-adrenoceptor downregulation is associated principally with an increased intracellular transit time during recycling. This could promote the diversion of receptors into protease-containing compartments, where there is an irreversible commitment to downregulation prior to loss of radioligand binding activity.

Adrenergic beta-Agonists↗
PubMed1999

Agonist-induced sorting of human beta2-adrenergic receptors to lysosomes during downregulation.

During prolonged exposure to agonist, beta2-adrenergic receptors undergo downregulation, defined by the loss of radioligand binding sites. To determine the cellular basis for beta2-adrenergic receptor downregulation, we examined HEK293 cells stably expressing beta2-adrenergic receptors with an N-terminal epitope tag. Downregulation was blocked by leupeptin, a cysteine protease inhibitor, but not by pepstatin, an inhibitor of aspartate proteases. Immunofluorescence microscopy of cells treated with agonist for 3-6 hours in the presence of leupeptin showed beta2-adrenergic receptors, but not transferrin receptors, localizing with the lysosomal protease cathepsin D, and with lysosomes labeled by uptake of a fluorescent fluid-phase marker. No localization of beta2-adrenergic receptors with lysosomal markers was observed in the absence of leupeptin, most likely due to proteolysis of the epitope. The proton pump inhibitor, bafilomycin A1, significantly inhibited this agonist-induced redistribution of beta2-adrenergic receptors into lysosomes, causing receptors to accumulate in the rab11-positive perinuclear recycling compartment and slowing the rate of beta2-adrenergic receptor recycling. Control experiments showed that leupeptin had no nonspecific effects on the cellular trafficking of either beta2-adrenergic receptors or transferrin receptors. Although cAMP alone caused a small decline in receptor levels without redistributing beta2-adrenergic receptors from the plasma membrane, this effect was additive to that seen with agonist alone, suggesting that agonist-induced beta2-adrenergic receptor downregulation resulted largely from cAMP-independent mechanisms. These results indicate that during agonist-induced downregulation, a significant fraction of beta2-adrenergic receptors are specifically sorted to lysosomes via the endosomal pathway, where receptor degradation by cysteine proteases occurs. These results provide a cellular explanation for the loss of radioligand binding sites that occurs during prolonged exposure to agonist.

Adrenergic beta-2 Receptor Agonists↗
PubMed1996

The management of chronic fissure in-ano with botulinum toxin.

Five patients with a chronic fissure in-ano each received an injection of Clostridium botulinum type A toxin into the lower internal anal sphincter. A mean lowering of maximum resting anal pressure by 23.3 (SEM 5.6) cm H2O was achieved within seven days. Maximum voluntary squeeze pressures were not significantly altered. Anal compliance increased in all cases. Healing of the fissure with an apparent reduction in anal sensation occurred in three of the patients and partial resolution of symptoms in the other two. No adverse effects resulted from injections of the toxin. A controlled trial to compare the relative efficacies of botulinum toxin and lateral sphincterotomy is required.

Adult↗
PubMed1993

Measurement of inspiratory muscle performance with incremental threshold loading: a comparison of two techniques.

BACKGROUND: Incremental threshold loading (ITL) is a test of inspiratory muscle performance which is usually performed by breathing through a weighted inspiratory plunger, the load on the inspiratory muscles being increased by externally adding weights to the intake valve. This is not a true threshold device and may be inaccurate. This method was compared with a true threshold device consisting of a solenoid valve which only opens to supply air at a predetermined negative mouth pressure. METHODS: Six naive, normal subjects (three men and three women) aged 22-24 years underwent three tests using each system. The inspiratory loads were increased every minute by equivalent amounts, -10 cm H2O with the solenoid valve and by 50 g with the weighted plunger, until the subjects could not inspire or sustain inspiration for a full minute. Six experienced subjects (four men and two women) aged 23-41 years were subsequently randomised to perform ITL with the solenoid valve, twice with the breathing pattern fixed and twice free. RESULTS: The solenoid valve generated a more accurate mouth pressure response and was less variable at higher loads than the weighted plunger. The work performed (expressed as the pressure-time product) was less with the solenoid valve but was more reproducible. ITL with the solenoid valve was not influenced by controlling the breathing pattern of the subjects. CONCLUSIONS: The solenoid valve has several features that make it superior to the weighted plunger as a device for ITL. It generates a more accurate mouth pressure response which is less variable at higher loads. Increases in load are smoother and quicker to introduce. ITL with the solenoid valve is not influenced by varying breathing patterns and does not require any external regulation.

Adult↗
PubMed1991

Doppler ultrasound studies in renal arteries of normal newborn babies.

The renal arteries of 89 healthy full-term infants were examined using duplex Doppler ultrasonography to establish a normal range for renal blood flow velocity in the first 3 days of life. In the first 24 h a wide range of renal blood flow velocities was noted with a statistically significant decrease in Pourcelot's index over the next 2 days.

Humans↗