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Biomedical subjects

L Best

Publications and source records attributed to L Best.

At least 37 records · Page 2Linked to original sources
PubMed1999

Trioses and related substances: tools for the study of pancreatic beta-cell function.

Trioses, such as D-glyceraldehyde, have been used extensively for the study of stimulus-secretion coupling mechanisms in pancreatic beta-cells. It is generally assumed that trioses enter the glycolytic pathway at the triose phosphate level, and stimulate insulin release in a manner analogous to glucose. This review focuses on a number of triose effects that are not entirely consistent with this model. These effects are likely to result, at least in part, from the actions of alpha-ketoaldehydes. One such compound, methylglyoxal, appears to be a major contaminant of triose preparations, and exerts effects on the beta-cell identical to some of those evoked by glyceraldehyde. A related substance, hydroxypyruvaldehyde, is a product of triose autoxidation, which could exert similar effects. Study of the actions of trioses and alpha-ketoaldehydes could assist our understanding of cellular physiology, in general, and beta-cell function, in particular. These substances are also likely to be of pathophysiological importance, especially in the context of sugar toxicity and autoxidative cell damage.

Animals↗
PubMed1999

Regulation of a volume-sensitive anion channel in rat pancreatic beta-cells by intracellular adenine nucleotides.

1. The patch-clamp technique in the whole-cell configuration was used to measure the effects of intracellular adenine nucleotides on activity of the volume-sensitive anion channel in single, isolated rat pancreatic beta-cells. 2. In the absence of intracellular nucleotides, swelling of cells with a hypertonic pipette solution failed to activate the conductance. Addition of ATP over the range 2-10 mM maintaining the same degree of hypertonicity caused a progressive activation of the conductance. An increase in ATP produced a similar activation of the conductance in non-swollen cells, albeit with reduced current amplitudes. 3. Activation of the conductance was also observed in the presence of ATPgammaS, adenylyl imidophosphate (AMP-PNP), ADP, diadenosine tetraphosphate and GTPgammaS. Neither ADP nor GDPbetaS inhibited activation of the conductance by ATP. 4. It is concluded that activity of the beta-cell volume-sensitive anion channel can be modulated by changes in intracellular concentrations of ATP within the physiological concentration range by a mechanism that does not require nucleotide hydrolysis. Activity of the channel does not appear to be modulated by a G protein-coupled mechanism.

Adenine Nucleotides↗
PubMed1999

Methylglyoxal causes swelling and activation of a volume-sensitive anion conductance in rat pancreatic beta-cells.

Membrane potential and whole-cell current were studied in rat pancreatic beta-cells using the 'perforated patch' technique and cell volume measured by a video-imaging method. Exposure of beta-cells to the alpha-ketoaldehyde methylglyoxal (1 mM) resulted in depolarization and electrical activity. In cells voltage-clamped at -70 mV, this effect was accompanied by the development of inward current noise. In voltage-pulse experiments, methylglyoxal activated an outwardly rectifying conductance which was virtually identical to the volume-sensitive anion conductance previously described in these cells. Two inhibitors of this conductance, 4,4'-dithiocyanatostilbene-2,2'-disulfonic acid (DIDS) and 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB), also inhibited the depolarization and inward current evoked by methylglyoxal. Methylglyoxal increased beta-cell volume to a relative value of 1.33 after 10 min with a gradual return towards basal levels following withdrawal of the alpha-ketoaldehyde. None of the effects of methylglyoxal was observed in response to t-butylglyoxal which, unlike methylglyoxal, is a poor substrate for the glyoxalase pathway. Methylglyoxal had no apparent effect on beta-cell K+ channel activity. It is suggested that the metabolism of methylglyoxal to D-lactate causes beta-cell swelling and activation of the volume-sensitive anion channel, leading to depolarization. These findings could be relevant to the stimulatory action of D-glucose, the metabolism of which generates significant quantities of L-lactate.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1999

Surgical treatment of posttraumatic cystic and tethered spinal cords.

Posttraumatic syringomyelia as a cause of progressive neurologic deterioration has been well described. More recently, the noncystic posttraumatic tethered cord has been associated with identical progressive neurologic deterioration. A retrospective analysis of patients treated surgically with spinal cord untethering and/or cyst shunting to arrest a progressive myelopathy from a posttraumatic tethered and/or cystic cord was performed. Emphasis was on outcome using the American Spinal Injury Association (ASIA) sensory and motor scoring systems. During an 18-month period from May 1993 to December 1994, 70 patients with spinal cord injury were operated upon for tethered and/or cystic spinal cords because of a progressive myelopathy and deteriorating ASIA sensory/motor scores. Fifty-nine patients had follow-up data 1 year postoperatively. At the 1 year follow-up, there was small improvement in light touch sensory scores (0.67 points), pinprick scores (1.3 points), and motor scores (0.41 points) demonstrating that the progression of the myelopathic process was arrested. Thirty-four of these 59 patients had no previous surgery to their spinal cords. At 1 year follow-up, light touch scores improved on average 2.38 points, pinprick scores 3.88 points (p < 0.05), and motor scores 1.47 points, suggesting better outcome with first-time surgery. Of this latter group, 64.3% regained a lost function, 62.5% saw improvement in spasticity, 55.6% had substantial improvement in neurogenic pain, and 95.8% felt that surgery prevented further neurologic deterioration.

Adolescent↗
PubMed1998

Effects of methylglyoxal on rat pancreatic beta-cells.

The addition of the alpha-ketoaldehyde methylglyoxal (0.5 or 1 mmol/L) to single isolated rat pancreatic beta-cells caused a rapid, marked depolarization resulting in electrical activity. This effect of methylglyoxal on beta-cell was reversible upon removal of the alpha-ketoaldehyde, and could be inhibited by the anion channel blockers 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) and 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB). Methylglyoxal also resulted in elevated cytosolic [Ca2+] and an intracellular acidification in intact rat islets. In perifused islets, methylglyoxal provoked a modest, transient stimulation of secretion but inhibited glucose-induced insulin release. Incubation of islets with methylglyoxal resulted in the formation of large quantities of D-lactate, indicating metabolism of the alpha-ketoaldehyde via the glyoxalase pathway. The effects of methylglyoxal on beta-cell membrane potential, cytosolic [Ca2+] and intracellular pH were also observed in response to phenylglyoxal which is also effectively metabolized via the glyoxalase pathway. However, t-butylglyoxal which is poorly metabolized via the glyoxalase pathway, caused neither depolarization of the membrane potential nor intracellular acidification, but did inhibit glucose-induced insulin release. These findings suggests that the depolarization and acidification evoked by methyl- and phenylglyoxal are dependent upon their metabolism via the glyoxalase pathway. The possible mechanisms coupling alpha-ketoaldehyde metabolism via the glyoxalase pathway with membrane depolarization are discussed.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1998

Regulatory volume increase in rat pancreatic beta-cells.

This study investigated regulatory volume increase (RVI) in rat pancreatic beta-cells. Volume changes in isolated beta-cells were measured by a video-imaging method. Cell shrinkage was induced by exposure to solutions made hypertonic by the addition of 100 mM mannitol. In HEPES-buffered solutions, beta-cells exhibited an RVI which was almost completely abolished by 10 microM bumetanide. These data indicate that Na+-2Cl--K+ cotransporters make a major contribution to RVI in beta-cells. In HCO3--buffered solutions, however, an RVI was observed in the presence of 10 microM bumetanide. This bumetanide-insensitive component of RVI was inhibited by 100 microM amiloride or 100 microM 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS). These data suggest that, in addition to the Na+-2Cl--K+ cotransporter, functionally coupled Na+-H+ exchangers and Cl--HCO3- exchangers may also contribute to RVI in pancreatic beta-cells.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1998

Chemical structure of bismuth compounds determines their gastric ulcer healing efficacy and anti-Helicobacter pylori activity.

The recognition of the role of Helicobacter pylori in the pathogenesis of peptic ulcer disease has led to renewed interest in bismuth pharmacology since bismuth compounds have both anti-Helicobacter pylori and ulcer healing properties. The precise chemical structure of current bismuth compounds is not known. This has hindered the development of new and potentially more efficacious formulations. We have created two new compounds, 2-chloro-1,3-dithia-2-bismolane (CDTB) and 1,2-[bis(1,3-dithia-2-bismolane)thio]ethane (BTBT), with known structure. In a rat model of gastric ulceration, BTBT was comparable to, and CDTB was significantly less effective than colloidal bismuth subcitrate in healing cryoprobe-induced ulcers. However, both BTBT and CDTB inhibited H. pylori growth in vitro at concentrations <1/10 that of colloidal bismuth subcitrate. The effects on ulcer healing are not mediated by suppression of acid secretion, pepsin inhibition, or prostaglandin production. Since all treated animals received the same amount of elemental bismuth, it appears that the efficacy of bismuth compounds varies with compound structure and is not simply dependent on the delivery of bismuth ion. Because the structure of the novel compounds is known, our understanding of the relationship of bismuth compound structure and to biologic activity will increase. In the future it may be possible to design other novel bismuth compounds with more potent anti-H. pylori and ulcer healing effects.

Animals↗
PubMed1998

Effects of sulphonylureas on the volume-sensitive anion channel in rat pancreatic beta-cells.

1. The volume-sensitive anion conductance in rat pancreatic beta-cells was studied directly using the conventional whole-cell and perforated patch recording techniques, and indirectly by measuring 3H-taurine efflux from pre-loaded, perifused islets. 2. Using the conventional whole-cell recording configuration, activation of the outwardly-rectifying, DIDS-sensitive conductance was induced by glibenclamide (10 microM) but not by tolbutamide (100 microM) nor by meglitinide (20 microM). A high concentration of glibenclamide (100 microM) caused a voltage-and time-dependent inhibition of the conductance. Tolbutamide had a modest inhibitory effect on swelling-induced inward currents. 3. In perforated patch recordings, glibenclamide, tolbutamide and meglitinide were all without effect on the conductance, although activation could be induced under these conditions by exposure to a hypotonic bath solution. 4. The rate of efflux of 3H-taurine, a marker for activity of the volume-sensitive anion channel, from preloaded, perifused islets was markedly stimulated by exposure to a hypotonic solution. However, glibenclamide and tolbutamide were both without effect. 5. Electrical activity of beta-cells in response to glibenclamide or tolbutamide was not inhibited by 4,4'-dithiocyanatostilbene-2,2'-disulphonic acid (DIDS), an inhibitor of the volume-sensitive anion channel. 6. It is concluded that activity of the volume-sensitive anion conductance in rat pancreatic beta-cells is not modulated by the sulphonylurea receptor. The activation of the conductance by glibenclamide in whole-cell recordings could be the result of a non-specific interaction of the drug with plasma membrane lipids.

Animals↗
PubMed1998

Population screening in the NHS: a systematic pathway from evidence to policy formulation.

In 1994 the Chief Medical Officer of England set out a framework for the evaluation and implementation of national screening programmes in the National Health Services (NHS). The framework highlighted the importance of the link between research evidence and the formulation of national policy. It also stressed the necessity for monitoring, evaluation and quality control as integral components for all new screening programmes. There is now an established link between the Health Technology Assessment programme of the NHS Research and Development Directorate and the NHS's new policy advisory group, the National Screening Committee. The objective of this systematic approach is to ensure that screening programmes are not introduced into the NHS unless there is robust evidence that benefit outweighs harm. The Population Screening Panel, an advisory panel of the NHS Health Technology Assessment programme, has the responsibility for determining priorities in research on proposed or existing population screening programmes. The National Screening Committee has a remit to consider this research evidence and to advise government ministers and the NHS on the appropriateness of the implementation, development and modification of national screening programmes. The example of prostatic cancer screening is presented as an illustration of how the NHS is developing a systematic approach to the implementation of screening policy based upon the strategic commissioning of research evidence.

Cost-Benefit Analysis↗
PubMed1997

Glucose-induced swelling in rat pancreatic beta-cells.

1. Changes in relative cell volume in response to hypotonic solutions and glucose were studied in single isolated rat pancreatic beta-cells using a video-imaging technique. beta-cell electrical activity was recorded under similar conditions using the perforated patch technique. 2. Exposure of beta-cells to hypotonic solutions (10 and 33% hypotonicity) caused an immediate increase in cell volume to relative values of 1.09 and 1.33, respectively. This was followed by a gradual regulatory volume decrease. 3. Raising the concentration of glucose from 4 to 20 mM or 12 mM (with substitution of mannitol) increased beta-cell volume by 12 and 10%, respectively. This effect of glucose persisted when CO2+ was added to inhibit insulin release. Glucose-induced volume increases were sustained for the duration of exposure to elevated hexose concentration. The addition of 16 mM 3-O-methylglucose, which is transported into the beta-cell but not metabolized, produced only a transient 5% increase in beta-cell volume. 4. Exposure of beta-cells to a 15% hypotonic solution resulted in a transient depolarization and electrical activity. Raising the glucose concentration to 20 or 12 mM caused a sustained depolarization and generation of electrical activity. However, the addition of 16 mM 3-O-methylglucose had no effect on beta-cell membrane potential. The glucose-induced increase in volume and induction of electrical activity, when measured in single beta-cells simultaneously, showed comparable kinetics. 5. The secretion of insulin from intact pancreatic islets was stimulated by exposure to hypotonic solutions (10-33% hypotonicity). A 15% hypotonic solution stimulated insulin release to a peak value comparable to that elicited by raising the glucose concentration from 4 to 20 mM. Whereas hypotonic solutions caused a transient stimulation of insulin release, the effect of glucose was sustained. 6. It is suggested that glucose increases the volume in rat pancreatic beta-cells by a mechanism dependent upon metabolism of the sugar. The extent of cell swelling evoked by raised glucose concentrations is sufficient to depolarize the cells and induce electrical and secretory activity and may involve activation of a volume-sensitive anion conductance.

Animals↗
PubMed1997

Glucose and alpha-ketoisocaproate induce transient inward currents in rat pancreatic beta cells.

The perforated patch technique was used to study changes in membrane potential and whole-cell currents in single isolated rat pancreatic beta-cells during stimulation with glucose or alpha-ketoisocaproate. Increasing the glucose concentration from 4 to 20 mmol/l, or addition of 15 mmol/l alpha-ketoisocaproate, caused depolarization and, in most cases, initiation of action potentials. Under voltage-clamp conditions close to a potassium equilibrium potential (EK) (-60 to -70 mV) these effects were accompanied by the appearance of transient inward currents. These transient currents resembled those elicited during cell swelling in response to a 10% hypotonic bath solution, a manoeuvre which also caused beta-cell depolarization and electrical activity. Tolbutamide (0.2 mmol/l), in the absence of glucose depolarized beta-cells but did not induce transient inward currents. Nutrient-induced electrical activity and inward currents were abolished by the anion channel inhibitors 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid and 5-nitro-2-(3-phenylpropylamino) benzoic acid, compounds which also inhibited glucose-induced insulin release. It is concluded that nutrient secretagogues induce transient inward currents in isolated rat beta-cells, possibly by activating a volume-sensitive anion conductance. These inward currents could enhance the intensity of electrical, and hence secretory, activity in the beta-cell during nutrient stimulation.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1996

Insulinotropic action of methyl pyruvate: secretory, cationic, and biosynthetic aspects.

Methyl pyruvate was found to exert a dual effect on insulin release from isolated rat pancreatic islets. A positive insulinotropic action prevailed at low concentrations of D-glucose, in the 2.8 to 8.3 mM range, and at concentrations of the ester not exceeding 10.0 mM. It displayed features typical of a process of nutrient-stimulated insulin release, such as decreased K+ conductance, enhanced Ca2+ influx, and stimulation of proinsulin biosynthesis. A negative insulinotropic action of methyl pyruvate was also observed, however, at a high concentration of D-glucose (16.7 mM) and/or at a high concentration of the methyl ester (20.0 mM). It was apparently not attributable to any adverse effect of methyl pyruvate on ATP generation, but might be due to hyperpolarization of the plasma membrane. The ionic determinant(s) of the latter change was not identified. The dual effect of methyl pyruvate probably accounts for an unusual time course of the secretory response, including a dramatic and paradoxical stimulation of insulin release upon removal of the ester.

Animals↗
PubMed1996

Insulinotropic action of methyl pyruvate: enzymatic and metabolic aspects.

The metabolism of methyl pyruvate was compared to that of pyruvate in isolated rat pancreatic islets. Methyl pyruvate was found to be more efficient than pyruvate in supporting the intramitochondrial conversion of pyruvate metabolites to amino acids, inhibiting D-[5-3H]glucose utilization, maintaining a high ratio between D-[3,4-14C]glucose or D-[6-14C]glucose oxidation and D-[5-3H]glucose utilization, inhibiting the intramitochondrial conversion of glucose-derived 2-keto acids to their corresponding amino acids, and augmenting 14CO2 output from islets prelabeled with L-[U-14C]glutamine. Methyl pyruvate also apparently caused a more marked mitochondrial alkalinization than pyruvate, as judged from comparisons of pH measurements based on the use of either a fluorescein probe or 14C-labeled 5,5-dimethyl-oxazolidine-2,4-dione. Inversely, pyruvate was more efficient than methyl pyruvate in increasing lactate output and generating L-alanine. These converging findings indicate that, by comparison with exogenous pyruvate, its methyl ester is preferentially metabolized in the mitochondrial, rather than cytosolic, domain of islet cells. It is proposed that both the positive and the negative components of methyl pyruvate insulinotropic action are linked to changes in the net generation of reducing equivalents, ATP and H+.

Alanine Transaminase↗
PubMed1996

A volume-activated anion conductance in insulin-secreting cells.

The whole-cell patch-clamp recording technique was used to measure volume-activated currents in K+-free solutions in RINm5F and HIT-T15 insulinoma cells and in dispersed rat islet cells. Cell swelling, induced by intracellular hypertonicity or extracellular hypotonicity, caused activation of an outwardly rectifying conductance which could be subsequently inactivated by hypertonic extracellular solutions. The conductance required adenosine 5'-triphosphate (ATP) in the pipette solution but was Ca2+ independent. Na+ and Cl- substitution studies suggested that the swelling-activated current is Cl- selective with a halide permeability sequence of Br > Cl > I. The conductance was reversibly inhibited by the anion channel inhibitors 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) and by 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB). Further evidence for a volume-activated anion conductance was provided by studies of volume regulation in insulin-secreting cells. When RINm5F cells were exposed to a hypotonic medium, the initial cell swelling was followed by a regulatory volume decrease (RVD). This RVD response was also inhibited by DIDS and by NPPB. These data therefore provide evidence for a volume-activated anion conductance in insulin-secreting cells which could be involved in the RVD following osmotic stress. A possible role for the conductance in hypotonically induced insulin release is also discussed.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗