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Biomedical subjects

S J Taylor

Publications and source records attributed to S J Taylor.

18 recordsLinked to original sources
PubMed1992

In vivo occupancy of histamine H3 receptors by thioperamide and (R)-alpha-methylhistamine measured using histamine turnover and an ex vivo labeling technique.

In the brain, the H3 type of histamine receptor has a pre-synaptic autoreceptor inhibitory role which regulates neuronal release and synthesis of histamine. To examine the interaction of the selective H3 receptor antagonist thioperamide with H3 receptors in the brain in vivo, we have used a functional and non-functional measurement of H3 receptor occupancy. In three species (rat, guinea-pig and mouse) peripheral administration of thioperamide caused dose-related increases in histamine turnover in the cerebral cortex (whole brain was examined in the mouse) and, in the same tissues, inhibited the ex vivo binding of the selective H3 receptor agonist [3H](R)-alpha-methylhistamine ([3H]-RAMH). The peak effect of thioperamide to inhibit ex vivo binding of [3H]RAMH was observed approximately 30 min after i.p. administration, whilst the maximum increase in histamine turnover did not occur until after at least 100 min. At a pretreatment time of 30 min, the ED50 of thioperamide to inhibit ex vivo binding of [3H]RAMH binding in the rat, guinea-pig and mouse brain was found to be 2.0 +/- 0.2, 4.8 +/- 0.6 and 2.6 +/- 0.3 mg/kg (mean +/- SEM, N = 4), respectively. We have also examined the effect of peripheral administration of RAMH on ex vivo binding of [3H]RAMH in rat cortex. Qualitatively and quantitatively similar results to those of thioperamide were observed following i.p. administration of RAMH to rats (ED50 = 3.9 +/- 0.4 mg/kg, mean +/- SEM, N = 4). An effect of RAMH on histamine turnover in rat cortex could not be determined as this compound displayed significant cross-reactivity with the antibodies used in the radioimmunoassay to measure histamine and telemethylhistamine. These data indicate that, following peripheral administration, both thioperamide and RAMH penetrate the brain where they can subsequently interact with H3 receptors. It would appear that binding of thioperamide to H3 receptors is linked with a concomitant increase in histamine turnover in the brain. In conclusion, the ex vivo binding technique, particularly when coupled with measurement of histamine turnover, should provide a valuable means for investigating the ability of any peripherally administered compound to cross the blood-brain barrier and subsequently interact with histamine H3 receptors.

Animals↗
PubMed1992

Regulation of phosphoinositide and phosphatidylcholine phospholipases by G proteins.

Two G proteins that regulate phosphoinositide phospholipase C in liver plasma membranes have been purified to homogeneity in both the heterotrimeric and dissociated forms. The heterotrimers contain a 42 kDa or 43 kDa alpha subunit and a 35 kDa beta subunit. The alpha subunits are not ADP-ribosylated by pertussis toxin and are closely related immunologically to members of the recently identified Gq class of G proteins. The specific phosphoinositide phospholipase C isozyme that responds to the G proteins has been determined to the beta 1 isozyme. GTP analogues stimulate phosphatidylcholine hydrolysis in rat liver plasma membranes. The nucleotide specificity and Mg2+ dependency of the response indicate that it is mediated by a G protein. Phosphatidic acid, diacylglycerol, choline and phosphorylcholine are the products, indicating that both phospholipase D and C activities are involved. Activation of phospholipase D is also indicated by the enhanced production of phosphatidyl-ethanol in the presence of ethanol.

Animals↗
PubMed1992

c-Src and mitosis.

The transforming potential and by inference the physiological function of the proto-oncoprotein pp60c-src closely correlate with the level of its protein tyrosine kinase activity. We have investigated the cell cycle-dependent regulation of this activity using mouse fibroblasts overexpressing chicken or mouse pp60c-src as a model system. During mitosis pp60c-src becomes phosphorylated at specific serine and threonine residues by p34cdc2. At the same time its tyrosine kinase activity, assayed in vitro, is increased approximately twofold and accessibility of its SH2 domain for binding relevant phosphotyrosine-containing ligands increases by about 15-fold. A kinase-defective mutant of pp60c-src exhibits a substantial (50-70%) decrease in phosphorylation at Tyr527 during mitosis. Phosphorylation of this residue negatively regulates kinase activity. Indirect evidence indicates a lesser decrease in wild-type pp60c-src Tyr527 phosphorylation during mitosis. Coordinate mutation of the mitosis-specific phosphorylation (MSP) sites in kinase-defective pp60c-src greatly reduces, though does not abolish, its mitosis-specific tyrosine dephosphorylation. Similarly, coordinate mutation of the three MSP sites in chicken pp60c-src or the corresponding two sites in mouse pp60c-src does not completely block mitotic stimulation of kinase activity. Thus, additional events beyond p34cdc2-mediated phosphorylation are involved in cell-cycle dependent regulation of pp60c-src activity. This is also suggested by the stimulation of pp60c-src kinase activity and decrease in phosphorylation of Tyr527 observed following treatment of fibroblasts with okadaic acid, a potent inhibitor of types 1 and 2A serine/threonine phosphatases. The potential role of cell cycle-dependent regulation of phosphatases and kinases acting on the regulatory tyrosine residue of pp60c-src is discussed.

Animals↗
PubMed1992

Characterization of histamine-H3 receptors controlling non-adrenergic non-cholinergic contractions of the guinea-pig isolated ileum.

1. In the presence of atropine, mepyramine and ranitidine, electric field stimulation of the guinea-pig isolated ileum longitudinal muscle-myenteric plexus preparation resulted in a two component non-adrenergic non-cholinergic contraction. The initial contraction had a duration of approximately 1 s whereas the second contraction lasted approximately 10 s. The second contraction was completely inhibited by tetrodotoxin (0.2 x 10(-6) M) with minimal effect on the initial contraction. Phentolamine (3 x 10(-6) M), propranolol (3 x 10(-6) M) and hexamethonium (10(-4) M), did not significantly reduce either component of the contractile response. 2. The neurokinin NK1 receptor antagonists, GR82334 and GR71251, produced concentration-related (EC50 = 564 and 173 nM respectively) inhibitions of the second contraction with no effect on the initial contraction. The neurokinin NK2 receptor antagonists MEN 10207 and Ac-Leu-Asp-Gln-Trp-Phe-Gly-NH2 (R 396), 1 x 10(-9)-10(-5) M, were without effect on either component of the contractile response. 3. Concentration-related inhibitions of the second contraction, with no effect on the initial contraction, were observed after inclusion of the histamine H3 receptor agonists (R)-alpha-methylhistamine (pD2 = 7.6), N alpha-methylhistamine (pD2 = 7.7) and N alpha,N alpha-dimethylhistamine (pD2 = 6.3). Histamine also inhibited the second contraction (pD2 = 6.2) in a concentration-related manner but produced a lower maximum inhibitory effect than the other agonists tested. 4. Inclusion of the H3 receptor antagonists, thioperamide, burimamide, impromidine and phenylbutanoylhistamine, caused parallel concentration-related rightward shifts in the concentration-response curve to (R)-alpha-methylhistamine. In each case, Schild analysis of these data gave slopes not significantly different from unity. Antagonist affinity values for thioperamide (pA2 = 8.2), burimamide (pA2 = 7.0) and impromidine (pA2 = 7.0) were consistent with values obtained in other assays of the H3 receptor. However, phenylbutanoylhistamine (pA2 = 5.8) and betahistine (pKB < 4) had affinities more than ten fold lower than values obtained in other assays of the H3 receptor.5. Exposure of the tissues to N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (10-6 M) for 7-30min followed by extensive washing, had no effect on basal contractions, but produced a rightward shift in the concentration-response curves to (R-alpha-methylhistamine, Nalpha"-methylhistamine, Nalpha",Nalpha-dimethylhistamine and histamine. This treatment also resulted in a decrease in the maximum inhibitory response obtainable. Apparent agonist affinity (pKD) values of 7.01, 7.06, 6.09 and 6.13 were estimated for (R)-alpha-methylhistamine, Nalpha-methylhistamine, Nalpha',Nalpha"-dimethylhistamine and histamine respectively.6. In conclusion, pharmacological analysis has revealed that histamine H3 receptors in the guinea-pig ileum modulate the release of non-adrenergic non-cholinergic neurotransmitters, one of which is probably substance P. In addition we have identified N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline as an irreversible antagonist at H3 receptors and have used this compound to estimate apparent affinity values of agonists at H3 receptors in this preparation.

Adrenergic alpha-Antagonists↗
PubMed1991

Two alpha subunits of the Gq class of G proteins stimulate phosphoinositide phospholipase C-beta 1 activity.

Two G protein alpha subunits were detected in preparations of GTP gamma S-dependent, phosphoinositide-specific phospholipase C-activating proteins from bovine liver membranes. Partial resolution of the two alpha subunits, of molecular mass 42 and 43 kDa, was achieved by Mono Q chromatography. Quantitation of the levels of each alpha subunit and reconstitution assays demonstrated that each possessed stimulatory activity towards the beta 1 isozyme of phospholipase C. Immunoblot analysis showed that the 42 kDa protein was immunologically related to alpha q, whereas the 43 kDa protein was related to alpha 11, another member of the Gq class. The data thus show that two different alpha subunits of the Gq class of G proteins stimulate phospholipase C-beta 1 Activity.

Animals↗
PubMed1991

Activation of the beta 1 isozyme of phospholipase C by alpha subunits of the Gq class of G proteins.

Many hormones, neurotransmitters and growth factors, on binding to G protein-coupled receptors or receptors possessing tyrosine kinase activity, increase intracellular levels of the second messengers inositol 1,4,5-trisphosphate and 1,2-diacylglycerol. This is due to activation of phosphoinositide-specific phospholipase(s) C (PLC), the isozymes of which are classified into groups, alpha, beta, gamma and delta. The beta, gamma and delta groups themselves contain PLC isozymes which have both common and unique structural domains. Only the gamma 1 isozyme has been implicated in a signal transduction mechanism. This involves association with, and tyrosine phosphorylation by, the ligand-bound epidermal growth factor and platelet-derived growth factor receptors, probably by means of the PLC-gamma 1-specific src homology (SH2) domain. Because EGF receptor-mediated tyrosine phosphorylation of PLC-gamma 1 stimulates catalytic activity in vitro and G proteins have been implicated in the activation of PLC, we investigated which PLC isozymes are subject to G protein regulation. We have purified an activated G protein alpha subunit that stimulates partially purified phospholipase C and now report that this G protein specifically activates the beta 1 isozyme, but not the gamma 1 and delta 1 isozymes of phospholipase C. We also show that this protein is related to the Gq class of G protein alpha subunits.

Animals↗
PubMed1991

Effect of general anaesthesia on the pharynx.

Conventional lateral radiography was used in 18 elderly male patients to investigate the changes induced by general anaesthesia in the upper airway. The effect of tongue traction under anaesthesia was studied similarly in another 11 patients. Following induction of anaesthesia, there were highly significant approximations to the posterior pharyngeal wall of the soft palate (median change 1.3 mm, 95% confidence interval (Cl) 0.3-2.6 mm; P = 0.006), tongue base (mean change 6.5 mm, 95% Cl 5.3-7.7 mm; P less than 0.001) and epiglottis (mean change 3.8 mm, 95% Cl 3.1-4.5 mm; P less than 0.001). Apparent radiographic occlusion of the airway occurred most consistently at the level of the soft palate (17 of 18 patients), sometimes at the level of the epiglottis (four patients), but the tongue base did not touch the posterior pharyngeal wall in any patient. Traction on the tongue failed to clear the nasopharyngeal obstruction. Attempted inspiration under anaesthesia caused major secondary collapse of the pharynx, with multiple sites of obstruction, similar to that found in obstructive sleep apnoea.

Aged↗
PubMed1991

Airway obstruction associated with the use of the Guedel airway.

Soft tissue lateral neck radiography was used in 22 male patients older than 60 yr, to determine the cause of pharyngeal airway obstruction during anaesthesia, before and after insertion of a Guedel airway. In six of the patients, the airway was radiologically and clinically clear with the head in the neutral position. Nine patients showed obstruction of the airway by a "shelf" of tongue, but seven were cleared clinically by dorsiflexion at the atlanto-occipital joint, and the remaining two by the Esmarch-Heiberg manoeuvre. In four of the 22 patients, the Guedel airway was lodged in the vallecula in the neutral position. This was cleared clinically by dorsiflexion at the atlanto-occipital joint in all these patients. In three patients the Guedel airway was obstructed by the epiglottis, but this was cleared by dorsiflexion at the atlanto-occipital joint in two; in the third patient, the Guedel airway slipped into the vallecula after dorsiflexion at the atlanto-occipital joint and remained there despite the Esmarch-Heiberg manoeuvre. There was only one instance in 66 trials of a clinically obstructed airway without an apparent radiological cause. However, there were 10 instances in 66 trials of a clinically clear airway with an apparent radiological cause for obstruction.

Aged↗
PubMed1991

Prescription and positioning: evaluating the physically disabled individual for wheelchair seating.

Within the past 10 years, technology has provided members of the seating team with new approaches in dealing with severely physically disabled children and adults. Positioning is often the first step in overall provision of technical aids. Before physically disabled individuals can operate augmentative communication devices, computer keyboards or other assistive or rehabilitative devices, they should be provided with the optimum seated posture from which to operate. The proximal stability provided by a therapeutically designed seating system will enhance motor potential. Presently, there are many approaches to providing dynamic seating. A thorough evaluation, with input from all team members including the client and his family is necessary to define clearly the goals for the seating device. Once these goals are defined, the team can investigate the possible technical solutions. Thorough ongoing re-evaluation and follow-up of both the client's needs and the possible technical solutions will ensure that persons with physical disabilities will be in the best possible posture to perform the tasks of daily living.

Activities of Daily Living↗
PubMed1991

Radiological study of the Laryngeal Mask.

Lateral soft-tissue radiography was used to determine the location of the Laryngeal Mask (LM) in relation to the larynx and surrounding structures in 24 elderly male patients undergoing general anaesthesia. In a majority of cases (16 of 24) the epiglottis was within the cuff of the mask but without causing discernable airway obstruction in any case. One case of backfolding of the cuff occurred, and there was one case of gross misplacement (also clinically undetected). Supplementary information was obtained in 13 patients by the use of fibre-optic endoscopy, via the lumen of the LM, confirming the inclusion of the epiglottis within the mask and demonstrating a characteristic distortion by the LM of the normal laryngeal anatomy. It is concluded that inclusion of the epiglottis within the LM is commonplace, and misplacements may occur without clinical evidence of a compromised airway.

Anesthesiology↗
PubMed1990

Alterations in vasopressin and angiotensin II receptors and responses during culture of rat liver cells.

Vasopressin and angiotensin II binding and responses were studied in hepatocytes in primary culture for 4 h and 24 h. After 24 h of culture, angiotensin II was completely ineffective in elevating cytosolic [Ca2+], whereas the maximum [Ca2+] response to vasopressin was decreased by 66% and the sensitivity to the hormone was decreased approx. 20-fold compared with values after 4 h of culture. The dissociation constant (KD) for vasopressin binding to the cells was not significantly changed during 24 h of culture, but the Bmax was decreased by 63% compared with 4 h of culture. There was also no change in the KD for angiotensin II binding from 4 h to 24 h, but the Bmax was decreased by 90%. After 24 h of culture, there was no change in the plasma membrane concentration of phosphatidylinositol 4,5-bisphosphate or in the basal cell concentration of inositol trisphosphate. However, the trisphosphate did not increase with 100 nM angiotensin II and the response to 100 nM vasopressin was reduced by 66% compared with that at 4 h. The effect of guanosine 5'-(3-O-thiol) triphosphate on the polyphosphoinositide phospholipase C activity of liver cell plasma membranes was also measured. There was no decrease in the degree of stimulation of the phospholipase by this nucleotide after 24 h of culture. It is concluded that the loss of vasopressin and angiotensin II responses in cultured liver cells is due in part to changes in receptors and also in their coupling to a guanine nucleotide binding protein.

Angiotensin II↗
PubMed1990

Purification of the hepatic vasopressin receptor using a novel affinity column.

A vasopressin receptor was purified, using a novel affinity column, from rat liver plasma membranes treated with guanosine 5'-(3-O-thio)triphosphate and solubilized with 0.8% cholate. Incubation of the membranes with the GTP analogue resulted in a dissociation of the receptor-guanine nucleotide regulatory protein complex. This manipulation, although resulting in a low-affinity state of the receptor, facilitated purification. The solubilized receptor was assayed using a new reconstitution procedure in which the soluble extracts were inserted into lipid vesicles composed of phosphatidylcholine and phosphatidylinositol. The receptor was purified by sequential chromatography on Q-Sepharose and hydroxyapatite. The use of a novel affinity column, a V1-vasopressin antagonist-agarose, resulted in a near-homogeneous preparation of a protein which exhibited an Mr = 58,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Autoradiography of purified receptor, as well as crude membrane preparations cross-linked to [125I]arginine vasopressin, also revealed a protein band with an approximate Mr = 58,000. These findings indicate that V1-antagonist affinity chromatography should be useful for purifying adequate amounts of the receptor for studies of structure and function.

Animals↗
PubMed1990

Purification from bovine liver membranes of a guanine nucleotide-dependent activator of phosphoinositide-specific phospholipase C. Immunologic identification as a novel G-protein alpha subunit.

Cholate-solubilized extracts from bovine liver plasma membranes preincubated with the nonhydrolyzable GTP analog guanosine 5'-(3-O-thio)triphosphate (GTP gamma S) displayed enhanced phosphoinositide-specific phospholipase C activity compared with extracts from membranes incubated without nucleotide or with ATP or GDP analog. Resolution of the GTP gamma S-elicited activator of phospholipase C was achieved using heparin-Sepharose which bound the phospholipase C activity. Recombination of non-adsorbed extract with salt-eluted phospholipase C activity resulted in a stimulation of enzyme activity. The GTP gamma S-dependent activator was purified, on the basis of its ability to activate partially purified phospholipase C, by sequential chromatography on Q-Sepharose, Sephacryl S-300, octyl-Sepharose, and Mono Q. The presence of G-protein beta subunits and the alpha subunits of Gi1, Gi2, and Gi3 was detected, by immunoblot analysis, in Mono Q-purified phospholipase C activator preparations. Resolution of the activator from these alpha subunits was achieved by incubation with pertussis toxin in the presence of millimolar NAD+ followed by rechromatography on Mono Q. The phospholipase C activator, thus resolved from ADP-ribosylated alpha i subunits, possessed an approximate Mr of 42 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and copurified with a substoichiometric amount of beta subunit. Immunoblot analysis of fractions from the final Mono Q column revealed cross-reactivity of the 42-kDa phospholipase C activator with antipeptide antibodies raised against residues 160-169 of alpha i1 and a region of sequence common to all known G-protein alpha subunits. The 42-kDa activator was not recognized by other alpha subunit-specific or common antibodies. These findings identify the purified phospholipase C activator as a novel G-protein alpha subunit. This may represent the active subunit of the pertussis toxin-insensitive G-protein mediating receptor-stimulated phosphoinositide breakdown in mammalian liver.

Adenosine Diphosphate Ribose↗
PubMed1990

"On-line" measurement of acetylcholinesterase release from the substantia nigra of the freely-moving guinea-pig.

Acetylcholinesterase is released from dopaminergic cells within the substantia nigra. The functional significance of this phenomenon has been studied in the freely-moving animal by a novel system for measuring acetylcholinesterase release from the substantia nigra "on-line" and in vivo. In the unanaesthetized guinea-pig the amount of acetylcholinesterase released was significantly greater than during anaesthesia, and release occurred in a more pulsatile manner. In addition, release of acetylcholinesterase could be evoked by either pharmacological or physiological manipulations, i.e. (1) a depolarizing concentration of potassium ions administered locally; (2) metamphetamine, administered systematically, which also resulted in increased locomotor activity; (3) drinking behaviour, elicited by presentation of a water bottle. Although all three treatments were accompanied by an increase in acetylcholinesterase release within the substantia nigra, potassium-evoked release did not cause any detectable change in behaviour. It is therefore suggested that release of the protein acetylcholinesterase within the substantia nigra is not necessarily a direct cause of locomotor activity: rather, it reflects diverse sensorimotor events.

Acetylcholinesterase↗
PubMed1979

Recovery mechanisms from acute hypoglycaemia in complete tetraplegia.

Acute hypoglycaemia has been achieved in tetraplegic subjects and in healthy controls using insulin. The recovery from hypoglycaemia has been followed by measuring appropriate substrate levels in blood. Abnormal responses of lactate and free fatty acid concentrations were observed; blood glucose recovery proceeded at a normal rate.

Adult↗
PubMedDate not supplied

Cell signalling through phospholipid breakdown.

There is much evidence that G-proteins transduce the signal from receptors for Ca(2+)-mobilizing agonists to the phospholipase C that catalyzes the hydrolysis of phosphoinositides. However, the specific G-proteins involved have not been identified. We have recently purified a 42 kDa protein from liver that activates phosphoinositide phospholipase C and cross-reacts with antisera to a peptide common to G-protein alpha-subunits. It is proposed that this protein is the alpha-subunit of the G-protein that regulates the phospholipase in this tissue. Ca(2+)-mobilizing agonists and certain growth factors also promote the hydrolysis of phosphatidylcholine through the activation of phospholipases C and D in many cell types. This yields a larger amount of diacylglycerol for a longer time than does the hydrolysis of inositol phospholipids. Consequently phosphatidylcholine breakdown is probably a major factor in long-term regulation of protein kinase C. The functions of phosphatidic acid produced by phospholipase D are speculative, but there is evidence that it is a major source of diacylglycerol in many cell types. The regulation of phosphatidylcholine phospholipases is multiple and involves direct activation by G-proteins, and regulation by Ca2+, protein kinase C and perhaps growth factor receptor tyrosine kinases.

Animals↗