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Biomedical subjects

R Ball

Publications and source records attributed to R Ball.

At least 19 recordsLinked to original sources
PubMed1996

Phospholipase C beta2 association with phospholipid interfaces assessed by fluorescence resonance energy transfer. G protein betagamma subunit-mediated translocation is not required for enzyme activation.

Phospholipase C beta2 (PLC beta2) is activated by G protein betagamma subunits and calcium. The enzyme is soluble and its substrate, phosphatidylinositol 4,5-bisphosphate (PIP2), is present in phospholipid membranes. A potential mechanism for regulation of this enzyme is through influencing the equilibrium association of the enzyme with membrane surfaces. In this paper we describe a fluorescence resonance energy transfer (FRET) method for measuring the association of PLC beta2 with phospholipid bilayers. The method allows equilibrium measurements to be made under a variety of conditions, including those that support enzymatic activity and ability to be regulated by G proteins. Using this method it was found that PLC beta2 bound to vesicles containing anionic lipids and demonstrated a selective and unique interaction with PIP2-containing vesicles. The FRET data were corroborated with a centrifugation based method for estimating the affinity of PLC beta2 for vesicles. Apparently different modes of association of PLC beta2 with vesicles of different composition can be distinguished based on alterations in resonance energy transfer efficiency. Association of PLC beta2 with PIP2 vesicles requires an intact lipid bilayer, is blocked by neomycin, and is not affected by D-myo-inositol 1,4,5-trisphosphate (D-IP3). G protein betagamma subunits do not alter the affinity of PLC beta2 for lipid bilayers and at the PIP2 concentrations used to measure betagamma-dependent stimulation of PLC activity, the majority of the PLC beta2 is already associated with the vesicle surface. Furthermore, under conditions where betagamma subunits strongly activate PLC activity, the extent of association with vesicles is unaffected by betagamma subunits or calcium. These results indicate that activation of PLC beta2 by G protein betagamma subunits or Ca2+ in vitro does not involve translocation to the vesicle surface.

Animals↗
PubMed1996

Regulation of cardiac Na+,Ca2+ exchange and KATP potassium channels by PIP2.

Cardiac Na+,Ca2+ exchange is activated by a mechanism that requires hydrolysis of adenosine triphosphate (ATP) but is not mediated by protein kinases. In giant cardiac membrane patches, ATP acted to generate phosphatidylinositol-4,5-bisphosphate (PIP2) from phosphatidylinositol (PI). The action of ATP was abolished by a PI-specific phospholipase C (PLC) and recovered after addition of exogenous PI; it was reversed by a PIP2-specific PLC; and it was mimicked by exogenous PIP2. High concentrations of free Ca2+ (5 to 20 microM) accelerated reversal of the ATP effect, and PLC activity in myocyte membranes was activated with a similar Ca2+ dependence. Aluminum reversed the ATP effect by binding with high affinity to PIP2. ATP-inhibited potassium channels (KATP) were also sensitive to PIP2, whereas Na+,K+ pumps and Na+ channels were not. Thus, PIP2 may be an important regulator of both ion transporters and channels.

Adenosine Triphosphate↗
PubMed1996

Practical marketing for dentistry. 5. Buyer behaviour.

Although the term 'buyer behaviour' may seem too commercial for the healthcare situation, in dentistry especially most patients 'buy' dental services and many of the principles of buyer behaviour are relevant to marketing in dentistry. This article looks at the factors that influence why people buy what they do.

Attitude to Health↗
PubMed1996

Practical marketing for dentistry. 3. Relationship marketing and patient/customer satisfaction.

In this article, we look at the philosophy of customer focus and value, and how dental practices can produce and deliver high customer value and satisfaction, to retain as well as attract their customers-the patients. Total quality concepts will also be discussed in the context of their relationship with marketing activities. In all cases, where 'customer' is referenced, this means 'patient' in the context of a dentistry, since patients are the customers, their requirements must be considered in targeting the marketing of a dental practice.

Consumer Behavior↗
PubMed1996

Practical marketing for dentistry. 2. The core concepts of marketing.

This series identifies the ideas and concepts behind modern marketing thinking, and suggests areas for consideration when creating a marketing 'culture' within general dental practices, dental supplies businesses, service suppliers, laboratories-or indeed any organisation which wants to succeed in today's challenging conditions.

Costs and Cost Analysis↗
PubMed1996

Practical marketing for dentistry. 1. What is marketing?

Do you really understand what 'marketing' means? Are you suspicious about the motives of those practising marketing? Is it ethical to promote dental and health services? Are we trying to make out that we offer more than we actually do? Is this a scheme dreamed up as a front for inferior services? The aim of this series is to demonstrate that marketing theory and concepts do have an ever increasing importance in today's dental practices. The series will explore different aspects of marketing thought and relate them to the practice environment, by use of practical examples and a case study.

Humans↗
PubMed1996

Angiotensin II-induced fluid phase endocytosis in human cerebromicrovascular endothelial cells is regulated by the inositol-phosphate signaling pathway.

The involvement of the early signaling messengers, inositol tris-phosphate (IP3), intracellular calcium, [Ca2+]i, and protein kinase C (PKC), in angiotensin II (AII)-induced fluid phase endocytosis was investigated in human brain capillary and microvascular endothelial cells (HCEC). ALL (0.01-10 microM) stimulated the uptake of Lucifer yellow CH, an inert dye used as a marker for fluid phase endocytosis, in HCEC by 50-230%. AII also triggered a fast accumulation of IP3 and a rapid increase in [Ca2+]i in cells loaded with the Ca(2+)-responsive fluorescent dye fura-2. The prompt AII-induced [Ca2+]i spike was not affected by incubating HCEC in Ca(2+)-free medium containing 2 mM EGTA or by pretreating the cultures with the Ca2+ channel blockers, methoxyverapamil (D600; 50 microM), nickel (1 mM), or lanthanum (1 mM), suggesting that the activation of AII receptors on HCEC triggers the release of Ca2+ from intracellular stores. The AII-triggered increases in IP3, [Ca2+]i, and Lucifer yellow uptake were inhibited by the nonselective AII receptor antagonist, Sar1, Val5, Ala8-AII (SVA-AII), and by the phospholipase C (PLC) inhibitors, neomycin and U-73122. By contrast, the protein kinase C (PKC) inhibitors, staurosporine and calphostin C, failed to affect any of these AII-induced events. This study demonstrates that increased fluid phase endocytotosis induced by AII in human brain capillary endothelium, an event thought to be linked to the observed increases in blood-brain barrier permeability in acute hypertension, is likely dependent on PLC-mediated changes in [Ca2+]i and independent of PKC.

Angiotensin II↗
PubMed1996

A profile of help-seeking Australian veterans.

While considerable information is available regarding American Vietnam veterans, surprisingly little has appeared concerning veterans of other nationalities who served in the Vietnam war. This paper provides a preliminary profile of help-seeking Australian veterans in order to afford a comparison with the available American data. Collected in the context of a review of the Vietnam Veterans Counselling Service (VVCS), demographic data suggest that the client population is similar in many ways to that of the American posttraumatic stress disorder (PTSD) Clinical Teams. Problems commonly reported by clients of VVCS included posttraumatic stress, relationship difficulties, anxiety, depression, and problems with pensions and benefits. A postal survey of a sub-sample of current clients revealed a mean score on the Combat Exposure Scale of 19.27 and a mean score on the Mississippi Scale for PTSD of 118.43. Again, these findings are broadly comparable with those of American help-seeking veterans.

Adaptation, Psychological↗
PubMed1996

Amino acid profile in Down's syndrome.

Fasting plasma and urinary amino acid concentrations were studied under carefully controlled conditions in 22 children with Down's syndrome and in age matched controls. The only significant difference between the groups was a higher mean plasma lysine concentration in Down's syndrome patients compared to controls.

Amino Acids↗
PubMed1995

Evidence for the role of protein kinase C in astrocyte-induced proliferation of rat cerebromicrovascular endothelial cells.

The proliferation of cerebral endothelial cells is a crucial step in neural angiogenesis and is a process responsive to changes in the surrounding environment. Serum-free medium conditioned by rat cortical astrocytes was found to accelerate DNA synthesis, induce transient activation of protein kinase C (PKC), and increase the endogenous phosphorylation of the PKC-specific substrate, the 85 kDa MARCKS protein, in rat cerebromicrovascular endothelial cells (RCEC). The stimulatory factor(s) in astrocyte conditioned media (ACM) were heat- and trypsin-sensitive and found to have an apparent molecular weight greater than 10 kDa. The potent PKC activator, 12-O-tetradecanoyl phorbol 13-acetate (TPA), also stimulated RCEC proliferation, whereas the inhibition of PKC by staurosporine caused a concomitant loss in ACM-induced PKC translocation, MARCKS protein phosphorylation and DNA synthesis. These findings implicate PKC activation as a critical early event in cerebral endothelial cell proliferation triggered by astrocyte-derived mitogen(s).

Animals↗
PubMed1995

The role of intracellular calcium and protein kinase C in endothelin-stimulated proliferation of rat type I astrocytes.

The increased expression of immunoreactive endothelin-1 (ET-1) in reactive astrocytes and its mitogenic effects on astrocytes and glioma cell lines, have implicated endothelins in the development of reactive gliosis. In this study, an increase in DNA synthesis in rat type I astrocytes was observed after cultures were transiently exposed to ET-1 for 15 min, suggesting that early signal transduction events are essential and sufficient for the propagation of the ET-1-induced mitogenic signal. Prompt increases in inositol triphosphate (IP3) formation and [Ca2+]i were observed upon the addition of ET-1 to these cells. The ET-1-evoked increase in [Ca2+]i consisted of an initial peak which was preserved in Ca(2+)-free medium, and a sustained phase which was abolished in Ca(2+)-free medium and partly attenuated by nifedipine. ET-1 also increased the activity of membrane-associated protein kinase C (PKC) and induced the in vivo phosphorylation of the 85 kD MARCKS protein, an endogenous PKC-specific substrate. The ET-1-evoked increases in DNA synthesis, IP3, [Ca2+]i, membrane PKC, and 85 kD MARCKS protein phosphorylation in rat cortical astrocytes were prevented by either the selective endothelin ETA receptor antagonist, BQ-123, or the phospholipase C (PLC)-specific inhibitor, U-73122. However, the inhibition of PKC activity did not affect ET-1-induced DNA synthesis in rat cortical astrocytes. These results suggest that ET-1-induced IP3 and/or [CA2+]i responses, but not the activation of PKC, are essential for the growth-factor like actions of ET-1 in rat cortical astrocytes.

Animals↗
PubMed1995

Baculovirus expression and purification of the second messenger enzyme phospholipase C-gamma 1, a tyrosine kinase substrate.

A rat cDNA encoding phospholipase C-gamma 1 (PLC-gamma 1) was expressed as a histidine-tagged fusion protein in insect cells utilizing the expression vector pBlueBacHis. The fusion protein was purified by Ni(2+)-agarose affinity chromatography to apparent homogeneity as defined by SDS-PAGE and Coomassie staining. Using a Triton X-100/PIP2 mixed micelle assay, (His6)-PLC-gamma 1 exhibited a calcium-dependent specific enzyme activity of 3 mumol/min/mg, a value similar to that reported for purified bovine brain PLC-gamma 1. Also similar to bovine brain PLC-gamma 1, (His6)-PLC-gamma 1 activity was stimulated by phosphatidic acid and inhibited by adenosine 5'monophosphate. (His6)-PLC-gamma 1 interacted directly with two known PLC-gamma 1 binding proteins, dynamin and the activated EGF receptor. Also, purified (His6)-PLC-gamma 1 was a tyrosine phosphorylation substrate for purified EGF receptor. These results suggest that (His6)-PLC-gamma 1 can be overexpressed as a functional enzyme in baculovirus-infected insect cells and purified by a one-step metal affinity chromatography procedure.

Animals↗