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Biomedical subjects

R S Martin

Publications and source records attributed to R S Martin.

At least 19 recordsLinked to original sources
PubMed2001

Fabrication and evaluation of a carbon-based dual-electrode detector for poly(dimethylsiloxane) electrophoresis chips.

The first carbon-based dual-electrode detector for microchip capillary electrophoresis (CE) is described. The poly(dimethylsiloxane) (PDMS)-based microchip CE devices were constructed by reversibly sealing a PDMS layer containing separation and injection channels to another PDMS layer containing carbon fiber working electrodes. End-channel amperometric detection was employed and the performance of the chip was evaluated using catechol. The response was found to be linear between 1 and 600 microM with an experimentally determined limit of detection (LOD) of 500 nM and a sensitivity of 30 pA/microM. Collection efficiencies for catechol ranged from 36.0 to 43.7% at field strengths of 260-615 V/cm. The selectivity that can be gained with these devices is demonstrated by the first CE-based dual-electrode detection of a Cu(II) peptide complex. These devices illustrate the potential for a rugged and easily constructed microchip CE system with an integrated carbon-based detector of similar scale.

Carbon↗
PubMed2001

Microchip capillary electrophoresis/electrochemistry.

Microfabricated fluidic devices have generated considerable interest over the past ten years due to the fact that sample preparation, injection, separation, derivatization, and detection can be integrated into one miniaturized device. This review reports progress in the development of microfabricated analytical systems based on microchip capillary electrophoresis (CE) with electrochemical (EC) detection. Electrochemical detection has several advantages for use with microchip electrophoresis systems, for example, ease of miniaturization, sensitivity, and selectivity. In this review, the basic components necessary for microchip CEEC are described, including several examples of different detector configurations. Lastly, details of the application of this technique to the determination of catechols and phenols, amino acids, peptides, carbohydrates, nitroaromatics, polymerase chain reaction (PCR) products, organophosphates, and hydrazines are described.

Amino Acids↗
PubMed2001

Microchip electrophoretic separation systems for biomedical and pharmaceutical analysis.

The application of microchip capillary electrophoresis (CE) systems to biomedical and pharmaceutical analysis is described and reviewed. Fabrication, instrumentation, and operation of the systems are discussed. An overview of applications is presented, covering four main areas: DNA sequencing, genetic analysis, immunoassays, and protein and peptide analysis. These systems have the potential to dramatically change the way that biochemical analyses are performed.

Animals↗
PubMed2001

Carbon paste-based electrochemical detectors for microchip capillary electrophoresis/electrochemistry.

The first reported use of a carbon paste electrochemical detector for microchip capillary electrophoresis (CE) is described. Poly(dimethylsiloxane) (PDMS)-based microchip CE devices were constructed by reversibly sealing a PDMS layer containing separation and injection channels to a separate PDMS layer that contained carbon paste working electrodes. End-channel amperometric detection with a single electrode was used to detect amino acids derivatized with naphthalene dicarboxaldehyde. Two electrodes were placed in series for dual electrode detection. This approach was demonstrated for the detection of copper(II) peptide complexes. A major advantage of carbon paste is that catalysts can be easily incorporated into the electrode. Carbon paste that was chemically modified with cobalt phthalocyanine was used for the detection of thiols following a CE separation. These devices illustrate the potential for an easily constructed microchip CE system with a carbon-based detector that exhibits adjustable selectivity.

Carbon↗
PubMed2001

Investigations into migraine pathogenesis: time course for effects of m-CPP, BW723C86 or glyceryl trinitrate on appearance of Fos-like immunoreactivity in rat trigeminal nucleus caudalis (TNC).

Clinical and preclinical studies suggest that 5-HT and nitric oxide (NO) mobilization within the trigeminovascular system is fundamental to the initiation of migraine attacks., e.g. m-chlorophenylpiperazine (m-CPP) and glyceryl trinitrate (GTN) induce headache in humans. 5-HT2B receptors are known to mediate NO-dependent vasorelaxation in peripheral blood vessels, raising the possibility that this receptor is implicated in the pathogenesis of the disease. Therefore, we measured the effects of 5-HT2B agonists (m-CPP or BW723C86) or GTN on trigeminal nerves by quantifying Fos expression in the rat TNC. m-CPP (0.1 mg/kg, i.v.) induced time-dependent elevations in Fos-LI in the rat TNC 2 h and 8 h after injection. In contrast, neither intravenous GTN (0.5 microg/kg per min, infused 20 min) nor BW723C86 (0.1 mg/kg, i.v.) increased Fos-LI at 2 h or 8 h after administration. These data are not consistent with the involvement of the 5-HT2B/2C receptors or NO in trigeminovascular activation, and by inference migraine, and suggest the contribution of some other unidentified pathway.

Animals↗
PubMed2001

Estimation of intra-abdominal pressure by bladder pressure measurement: validity and methodology.

BACKGROUND: Increased intra-abdominal pressure (IAP) is an adverse complication seen in critically ill, injured, and postoperative patients. IAP is estimated via the measurement of bladder pressure. Few studies have been performed to establish the actual relationship between IAP and bladder pressure. The purpose of this study was to confirm the association between intravesicular pressure and IAP and to determine the bladder volume that best approximates IAP. METHODS: Thirty-seven patients undergoing laparoscopy had intravesicular pressures measured with bladder volumes of 0, 50, 100, 150, and 200 mL at directly measured intra-abdominal pressures of 0, 5, 10, 15, 20, and 25 mm Hg. Correlation coefficients and differences were then determined. RESULTS: Across the IAP range of 0 to 25 mm Hg using all of the tested bladder volumes, the difference between IAP and intravesicular pressures (bias) was -3.8 +/- 0.29 mm Hg (95% confidence interval) and measurements were well correlated (R2 = 0.68). Assessing all IAPs tested, a bladder volume of 0 mL demonstrated the lowest bias (-0.79 +/- 0.73 mm Hg). When considering only elevated IAPs (25 mm Hg), a bladder volume of 50 mL revealed the lowest bias (-1.5 +/- 1.36 mm Hg). A bladder volume of 50 mL in patients with elevated IAP resulted in an intravesicular pressure 1 to 3 mm Hg higher than IAP (95% confidence interval). CONCLUSION: Intravesicular pressure closely approximates IAP. Instillation of 50 mL of liquid into the bladder improves the accuracy of the intravesicular pressure in measuring elevated IAPs.

Abdomen↗
PubMed2000

Identification of a locus for autosomal dominant polycystic liver disease, on chromosome 19p13.2-13.1.

Polycystic liver disease (PCLD) is characterized by the growth of fluid-filled cysts of biliary epithelial origin in the liver. Although the disease is often asymptomatic, it can, when severe, lead to complications requiring surgical therapy. PCLD is most often associated with autosomal dominant polycystic kidney disease (ADPKD); however, families with an isolated polycystic liver phenotype without kidney involvement have been described. The clinical presentation and histological features of polycystic liver disease in the presence or absence of ADPKD are indistinguishable, raising the possibility that the pathogenetic mechanisms in the diseases are interrelated. We ascertained two large families with polycystic liver disease without kidney cysts and performed a genomewide scan for genetic linkage. A causative gene, PCLD, was mapped to chromosome 19p13.2-13.1, with a maximum LOD score of 10.3. Haplotype analysis refined the PCLD interval to 12.5 cM flanked by D19S586/D19S583 and D19S593/D19S579. The discovery of genetic linkage will facilitate diagnosis and study of this underdiagnosed disease entity. Identification of PCLD will be instrumental to an understanding of the pathogenesis of cyst formation in the liver in isolated PCLD and in ADPKD.

Adult↗
PubMed2000

Dual-electrode electrochemical detection for poly(dimethylsiloxane)-fabricated capillary electrophoresis microchips.

The development of a poly(dimethylsiloxane)-based (PDMS-based) microchip electrophoresis system employing dual-electrode electrochemical detection is described. This is the first report of dual-electrode electrochemical detection in a microchip format and of electrochemical detection on chips fabricated from PDMS. The device described in this paper consists of a top layer of PDMS containing the separation and injection channels and a bottom glass layer onto which gold detection electrodes have been deposited. The two layers form a tight reversible seal, eliminating the need for high-temperature bonding, which can be detrimental to electrode stability. The channels can also be temporarily removed for cleaning, significantly extending the lifetime of the chip. The performance of the chip was evaluated using catechol as a test compound. The response was linear from 10 to 500 microM with an LOD (S/N = 3) of 4 microM and a sensitivity of 45.9 pA/microM. Collection efficiencies for catechol ranged from 28.7 to 25.9% at field strengths between 200 and 400 V/cm. Dual-electrode detection in the series configuration was shown to be useful for the selective monitoring of species undergoing chemically reversible redox reactions and for peak identification in the electropherogram of an unresolved mixture.

Dimethylpolysiloxanes↗
PubMed2000

Characterization of human recombinant alpha(2A)-adrenoceptors expressed in Chinese hamster lung cells using extracellular acidification rate changes.

1. Human alpha(2A)-adrenoceptors heterologously expressed in Chinese hamster lung (CHL) fibroblasts have been characterized pharmacologically using a cytosensor microphysiometer to measure ligand-induced extracellular acidification rate changes. 2. In untransfected CHL cells, noradrenaline had no effect at concentrations up to 100 microM. In alpha(2A)-adrenoceptor transfected cells the rank order of agonist potency was A-54741 (mean pEC(50)=8.96)>dexmedetomidine (8.88)>UK-14304 (8.42)>B-HT 920 (7.05)>noradrenaline (6.92). A-54741, UK-14304 and noradrenaline had the same maximum response while dexmedetomidine and B-HT 920 behaved as partial agonists. 3. The selective alpha(2)-adrenoceptor ligand rauwolscine antagonized acidification rate changes with an affinity independent of the agonist used; the affinity (mean pK(B)) against noradrenaline was 8.43. 4. The selective alpha(1)-adrenoceptor ligands prazosin and doxazosin (each 3 microM) had no effect on noradrenaline responses. 5. Acidification rate changes induced by each agonist were abolished by pre-treatment of cells with pertussis toxin. 6. These data suggest that agonist-induced acidification rate responses in CHL cells transfected with the human alpha(2A)-adrenoceptor are mediated exclusively by the recombinant protein, via pertussis toxin sensitive G(i/o) proteins.

Adrenergic alpha-Agonists↗
PubMed2000

Effects of cannabinoid receptor agonists on neuronally-evoked contractions of urinary bladder tissues isolated from rat, mouse, pig, dog, monkey and human.

This study investigated the cannabinoid receptor, known to inhibit neuronally-evoked contractions of the mouse isolated urinary bladder, in bladder sections isolated from mouse, rat, dog, pig non-human primate or human. The CB(1)-like pharmacology of the cannabinoid receptor in mouse isolated bladder observed previously was confirmed in this study by the rank order of agonist potencies: CP 55940>/=WIN 55212-2>HU 210>JWH 015>anandamide, the high affinity of the CB(1) selective antagonist, SR 141716A (apparent pK(B) 8.7), and the low affinity of the CB(2) antagonist, SR 144528 (apparent pK(B)<6.5). In these studies, SR 141716A (10-100 nM) significantly potentiated electrically-evoked contractions in this tissue by an undetermined mechanism. A similar rank order of agonist potencies was determined in rat isolated bladder sections (CP 55, 940> or =WIN 55212-2>JWH 015). In this tissue, the maximal inhibitory effect of all agonists was lower than in the mouse bladder. Indeed, the effects of both HU 210 and anandamide were too modest to quantify potency accurately. In the rat isolated bladder, SR 141716A (30 nM) or SR 144528 (100 nM), reversed the inhibitory effect of WIN 55212-2 (apparent pK(B) = 8.4 and 8.0, respectively) or JWH 015 (apparent pK(B) = 8.2 and 7.4, respectively). These findings may demonstrate pharmacological differences between the rat and mouse orthologues of the CB(1) receptor. Alternatively, they may be attributed to a mixed population of CB(1) and CB(2) receptors that jointly influence neurogenic contraction of the rat bladder, but cannot be differentiated without more selective ligands. WIN 55212-2 had no effect on electrically-evoked contractions of bladder sections isolated from dog, pig, cynomolgus monkey and human. These findings suggest that the effect of cannabinoid agonists to inhibit neurogenic contraction of the mouse and rat bladder is not conserved across all mammalian species.

Acetylcholine↗
PubMed2000

A novel frameshift mutation (2436insT) produces an immediate stop codon in the autosomal dominant polycystic kidney disease 2 (PKD2) gene.

BACKGROUND: Autosomal dominant polycystic kidney disease (ADPKD) is a genetically heterogeneous disorder that can be caused by mutations in at least three different genes. Several mutations have been identified in PKD1 and PKD2 genes. Most of the mutations found in PKD2 gene are predicted to cause premature termination of the protein. METHODS: We analysed an Argentinian family characterized previously as PKD2. The PKD2 gene was amplified from genomic DNA using 17 primer pairs and the products were analysed by heteroduplex analysis. PCR products that showed a variation by heteroduplex analysis were sequenced directly. The mutation was confirmed by sequencing relatives. The segregation of the mutation in this family was verified by restriction endonuclease digestion of PCR products obtained from genomic DNA of all family members. Results and conclusions. Here, we report a novel mutation present in an Argentinian family characterized as PKD2 by linkage analysis. The mutation, shared by all affected members of the family, is a thymidine insertion at position 2436 of the gene, which results in a translation frameshift and creates an immediate stop codon. This mutation is expected to lead to a truncated protein that lacks the interacting domain with the PKD1 gene product. The thymidine insertion abolished a Ddel restriction site, allowing a rapid test for detection of PKD2 carriers in the family.

Adult↗
PubMed2000

Somatostatin receptor scintigraphy: the definitive technique for characterizing vasoactive intestinal peptide-secreting tumors.

Vasoactive intestinal peptide-secreting tumors (VIPomas) are extremely rare and difficult to diagnose. The authors describe a patient who was found to have a VIPoma after 3 years of symptoms. Somatostatin receptor scintigraphy using indium-labeled octreotide localized her tumor and prompted a surgical resection. This is the preferred imaging study for the earliest, most accurate, and cost-effective identification of VIPomas and their metastases.

Female↗
PubMed1999

Isolated polycystic liver disease not linked to polycystic kidney disease 1 and 2.

Autosomal dominant polycystic liver disease occurs commonly in association with autosomal dominant polycystic kidney disease, types 1 and 2. It may also exist as a separate entity, genetically distinct from autosomal dominant polycystic kidney disease types 1 and 2, as has been recently established to exist in a Belgian family. We report here a large Argentinian family of Spanish-Belgian ancestry with autosomal dominant polycystic liver disease, where proximal and distal markers for both polycystic kidney disease 1 and 2 failed to demonstrate genetic linkage. The data support the notion that polycystic liver disease and autosomal dominant polycystic kidney disease may have separate chromosomal loci.

Adult↗
PubMed1998

Methamphetamine-induced alterations in dopamine transporter function.

Repeated methamphetamine (METH) administration has been shown to produce differing neurochemical as well as behavioral effects in rats. This study was designed to examine the effects of acute and chronic METH exposure on uptake and release of [3H]dopamine (DA) in cultured midbrain dopamine neurons to determine if persistent neuronal adaptations ensue. In addition, we have assessed DA D2 receptor function to determine if chronic METH alters this receptor. Fetal midbrain cultures were exposed to METH (1, 10 microM) for 5 days and dopaminergic function examined 1 or 7 days after drug removal. The ability of METH to release [3H]DA was compared to other releasing agents as well as several potent uptake inhibitors. Chronic exposure to a release-promoting concentration of METH resulted in either no change or a reduction in [3H]DA release upon subsequent METH challenge. Pretreatment with METH was also found to cause a decrease in the Bmax for [3H]raclopride binding, suggesting that persistently elevated DA levels cause a downregulation of DA D2 receptors. Examination of transporter kinetics utilizing initial velocity of uptake revealed that METH treatment caused a significant decrease in affinity (K(m)) for the substrate (DA), while not altering the maximal velocity of uptake (Vmax). Binding studies with [125I]RTI-55 revealed that there was no alteration in either the Bmax or Kd for this ligand, suggesting that the changes induced by METH treatment are due to alterations in K(m) and not in the number of DA transport sites. The results from these studies indicate that METH treatment produces a modification in transporter function which may be associated with both the altered uptake and release of [3H]DA. These changes have broad implications for the regulation of transporter activity not only because of the relevance to pre-synaptic mechanisms controlling neurotransmission, but also to the importance of the neuronal adaptation that occurs in response to chronic METH exposure.

Animals↗
PubMed1998

Prolonged dopamine and serotonin transporter inhibition after exposure to tropanes.

Cocaine and tropane analogs are known to interact with biogenic monoamine transporters by inhibiting amine uptake. Previous in vivo studies have demonstrated that some of these tropanes produce a longer lasting behavioral effect compared with cocaine. We have previously examined several tropane analogs and found a difference in their relative affinities for dopamine (DA) and serotonin (5-HT) transporters. The purpose of this study was to determine the recovery time of transporter function in vitro and in vivo comparing cocaine with the tropane analogs WF-11 (PTT, selective for DA transporters), WF-31 (selective for 5-HT transporters) and WF-23 (highly potent at both DA and 5-HT transporters). In vitro, using primary rat brain cultures of either midbrain or raphe regions, the recovery of the ability to transport either [3H]dopamine or [3H]serotonin, respectively was evaluated at 0, 3, 24, 48, 120 and 240 h after a 1 h exposure to cocaine and tropane analogs. The tropanes exhibited clearance half-lives ranging from 12 to 69 h, while cocaine, on the other hand, exhibited a clearance half-life of approximately 6 h. In studies utilizing [125I]RTI-55 binding, intraperitoneal injections of cocaine and WF-23 into the rat resulted in striatal clearance half-lives ex vivo that were almost identical to those obtained in vitro. These data suggest that the tropanes bind to and reduce transporter function for prolonged periods of time (up to 10-fold longer than cocaine) and those compounds with the highest affinity may produce a pseudo-irreversible inhibition of transporter function.

Animals↗
PubMed1998

Regulation of cell cyclic AMP in medullary thick ascending limb of Henle in a rat model of chronic renal failure.

Chronic renal failure (CRF) is accompanied by adaptive changes in electrolyte reabsorption in the thick ascending limb of Henle of surviving nephrons. To study the cellular mechanism of this adaptation, we measured intracellular cAMP in micro-dissected medullary thick ascending limb (mTAL) segments in rats with CRF. mTAL exhibited in CRF an increase of basal cAMP from 25.6 +/- 10.0 in controls to 65.8 +/- 11.3 fmol mm-1 tubule in CRF (P < 0.05). Vasopressin and calcitonin stimulated mTAL adenylate-cyclase in a dose-dependent manner in controls but failed to stimulate in CRF. Likewise, maximal stimulation with 10(-3) M 3-isobutyl-1-methylxanthine (IBMX) plus 10(-5) M forskolin increased cAMP in controls to 63.0 +/- 16.0 but not in CRF, where maximal stimulated values remained at 63.1 +/- 18.8 fmol mm-1 tubule (P NS). Alpha2-adrenoreceptor activation with clonidine at concentrations ranging from 10(-8) to 10(-6) M diminished cAMP production by 37% in CRF (P < 0.05), whereas no differences were found in controls. Thus, the basal intracellular cAMP is increased in rat mTAL in CRF. The finding that neither forskolin nor vasopressin were able to further augment intracellular cAMP would suggest that stimulatory pathways of the adenylate-cyclase system are activated in the basal state. However, mTAL cells in CRF seem to retain the response of normal epithelium to inhibitory pathways such as the one mediated by alpha2-adrenoreceptors.

1-Methyl-3-isobutylxanthine↗
PubMed1997

Technical complications of endovascular abdominal aortic aneurysm repair.

PURPOSE: Results from 34 endovascular repairs of abdominal aortic aneurysms are reviewed to identify technical complications and relate them to anatomic and technical features of the operation. METHODS: Twenty-one patients underwent attempted tube graft repair (mean follow-up, 13 months). Thirteen patients underwent placement of a bifurcated graft (mean follow-up, 7.2 months). RESULTS: Twenty-five patients (74%) underwent repair without technical complication (16 tube graft and nine bifurcated graft). Of five patients who had tube graft complications, two involved small iliac arteries and resulted in arterial injury. One of these patients needed a femorofemoral bypass procedure, and the other required conversion to standard operation. Two patients had distal leaks associated with the attachment system, and one patient had misplacement of the distal attachment system. The two patients who had leaks were followed-up; one required operation after 7 months, whereas the other leak sealed. The patient who had distal attachment system misplacement had a second endograft placed within the first to provide a distal seal. The four patients who had bifurcated graft complications involved two graft limb stenoses, one managed with a Palmaz stent and the other with balloon angioplasty. The patient treated with balloon angioplasty had graft thrombosis 1 week after the operation, which resulted in the need for a femorofemoral bypass procedure. Another bifurcated graft patient had a graft limb twist, which has resulted in chronic claudication. One patient had placement of a limb too proximal in the common iliac artery with chronic leak, and an open operation was performed 18 months later. CONCLUSIONS: Technical complications in this series seem to be associated with short distal necks, small iliac arteries, tortuous iliac arteries, and atherosclerosis at the aortic bifurcation. We believe that experience and understanding of these issues will reduce the risk of these complications in the future.

Aged↗