Biomedical subjects
Publications and source records attributed to G E Taylor.
4-Substituted 2-amino-6-(anilino)pyrimidines have been found to be selective inhibitors of DNA polymerase III, a replicative enzyme known to be essential in the DNA synthesis of Gram-positive bacteria. Among the analogues, 18 displayed an IC(50) of 10 microM against DNA polymerase III from Staphylococcus aureus.
Over the past 50 years, Lake Tahoe, an alpine lake located in the Sierra Nevada mountains on the border between California and Nevada, has seen a decline in water clarity. With significant urbanization within its borders and major urban areas 130 km upwind of the prevailing synoptic airflow, it is believed the Lake Tahoe Basin is receiving substantial nitrogen (N) input via atmospheric deposition during summer and fall. We present preliminary inferential flux estimates to both lake surface and forest canopy based on empirical measurements of ambient nitric acid (HNO3), ammonia (NH3), and ammonium nitrate (NH4NO3) concentrations, in an effort to identify the major contributors to and ranges of atmospheric dry N deposition to the Lake Tahoe Basin. Total flux from dry deposition ranges from 1.2 to 8.6 kg N ha-1 for the summer and fall dry season and is significantly higher than wet deposition, which ranges from 1.7 to 2.9 kg N ha-1 year-1. These preliminary results suggest that dry deposition of HNO3 is the major source of atmospheric N deposition for the Lake Tahoe Basin, and that overall N deposition is similar in magnitude to deposition reported for sites exposed to moderate N pollution in the southern California mountains.
1. The regulation of substance P (SP) responsiveness in acutely isolated nodose neurones from adult guinea-pigs was investigated using standard intracellular recording techniques. 2. In control neurones, SP produced no measurable electrophysiological effects. However, following incubation with serotonin (5-HT, 10 microM), 64% of neurones were depolarized by 10 +/- 0.6 mV (n = 84 of 132 neurones) by SP (100 nM). 5-HT-induced SP responses were inhibited by SR48968 (100 nM, n = 6), a neurokinin 2 (NK-2) receptor antagonist, but were unaffected by CP99,994 and SR142801, NK-1 and NK-3 receptor antagonists (n = 3 each), respectively. 3. 5-HT-induced unmasking of SP responses was maximal within 5 min. Increasing the 5-HT incubation time up to 120 min did not increase the mean response amplitude or the percentage of SP responsive neurones (P = 0.611 and 0.867, respectively). 4. 5-HT-induced unmasking of SP responses was dose dependent (EC50 = 14 nM). A 5-HT3 receptor agonist CPBG (1 microM), mimicked the unmasking effects of 5-HT (n = 10 of 19 neurones), while 5-CT (10 microM), a non-selective 5-HT agonist devoid of action at 5-HT3 receptors, did not (n = 18). ICS205-930 (1 microM), a 5-HT3 receptor antagonist, completely blocked the 5-HT-induced unmasking of SP responses (n = 10 of 10 neurones). 5. In 68% of the neurones tested, bath-applied 5-HT (10 microM) evoked a 178 +/- 29.5 nM increase in [Ca2+]i (n = 16), which was blocked by nominally zero [Ca2+]o (n = 4) or by ICS205-930 (1 microM, n = 4). Nodose neurones incubated with 5-HT in the presence of nominally zero [Ca2+]o did not respond to SP (n = 12 of 13 neurones) in Locke solution containing normal [Ca2+]o, indicating that the 5-HT-mediated elevation of [Ca2+]i is required for unmasking of SP responses. Calmidazolium (100 nM), a calmodulin inhibitor, inhibited the unmasking effects of 5-HT (n = 5 of 5 neurones). 6. Incubating neurones with the nitric oxide (NO) donors papaNONOate (1 mM, 15-30 min) or SNAP (50 microM, 30-60 min) unmasked depolarizing SP responses in 71% and 45% of the neurones studied, respectively. L-NMMA (30 microM), a NO synthase inhibitor, blocked 5-HT-induced unmasking of SP responses (n = 10 of 10 neurones). 7. In sum, these results suggest that stimulation of 5-HT3 receptors activates an intracellular signalling cascade that couples calcium-calmodulin and NO activation to NK-2 receptor unmasking in sensory neurones.
Neuroplastic changes in vagal afferents inflicted by allergic inflammation were examined in nodose ganglia (NG) removed from guinea pigs immunized to chick ovalbumin. In control NG neurons, substance P (SP; 0.1-10 microM) produces no discernable changes in membrane electrophysiological properties or [Ca2+]i. After exposing NG from immunized animals to the sensitizing antigen in vitro, 83% of the neurons were depolarized by 100 nM SP. SP also produces an inward current, an increase in membrane conductance, and an elevation of [Ca2+]i. Buffering [Ca2+]i with BAPTA blocked the [Ca2+]i rise and the SP depolarization, indicating that internal stores of Ca2+ are required. When protein synthesis was inhibited >96% (as determined by [3H] leucine incorporation), antigen challenge still unmasked SP responses. The SP response was maximal 30 min after antigen challenge, and it was evident for at least 8 hr in intact ganglia and for 3.5 d in isolated neurons. [beta-Ala8]Neurokinin A ([beta-Ala8]NKA; 10 nM), an NK-2 selective agonist, mimicked SP; selective NK-1 and NK-3 agonists were ineffective. The EC50 values for SP and [beta-Ala8]NKA membrane currents were 78 and 33 nM, respectively. Additionally, SR48968, an NK-2 receptor antagonist, blocked these responses. Thus, antigen challenge appears to unmask an NK-2 tachykinin receptor. These data further support the hypothesis that inflammatory mediators released during immediate hypersensitivity (allergic) reactions can produce profound effects on the excitability of sensory nerves. Unmasked NK-2 receptors may serve an excitatory autoreceptor function, provide a pathway for paracrine signaling between NG neurons, and contribute to ectopic sensory nerve activity.
1. Intracellular recordings were made in intact and acutely dissociated vagal afferent neurones (nodose ganglion cells) of the ferret to investigate the membrane effects of histamine. 2. In current-clamp or voltage-clamp recordings, histamine (10 microM) depolarized the membrane potential (10 +/- 0.8 mV; mean +/- S.E.M.; n = 27) or produced an inward current of 1.6 +/- 0.35 nA (n = 27) in approximately 80% of the neurones. 3. Histamine (10 microM) also blocked the post-spike slow after-hyperpolarization (AHP slow) present in 80% of these neurones (95 +/- 3.2%; n = 5). All neurones possessing AHPslow in ferret nodose were C fibre neurones; all AHPslow neurones had conduction velocities < or = 1 m s-1 (n = 7). 4. Both the histamine-induced inward current and the block of AHPslow were concentration dependent and each had an estimated EC50 value of 2 microM. These histamine-induced effects were mimicked by the histamine H1 receptor agonist 2-(2-aminoethyl) thiazole dihydrochloride (10 microM) and blocked by the H1 antagonists pyrilamine (100 nM) or diphenhydramine (100 nM). Schild plot analysis of the effect of pyrilamine on the histamine-induced inward current revealed a pA2 value of 9.7, consistent with that expected for an H1 receptor. Neither impromidine (10 microM) nor R(-)-alpha-methylhistamine (10 microM), selective H2 or H3 agonists, respectively, significantly affected the membrane potential, input resistance or AHPslow. 5. The reversal potential (Vrev) for the histamine-induced inward current was -84 +/- 2.1 mV (n = 4). The Vrev for the histamine response shifted in a Nernstian manner with changes in the extracellular potassium concentration. Alterations in the extracellular chloride concentration had no significant effect on the Vrev of the histamine response (n = 3). The Vrev for the AHPslow was -85 +/- 1.7 mV (n = 4). 6. These results indicate that histamine increases the excitability of ferret vagal afferent somata by interfering with two classes of potassium current: the resting or 'leak' potassium current (IK(rest)) and the potassium current underlying a post-spike slow after-hyperpolarization (IAHP). Both these effects can occur in the same neurone and involve activation of the same histamine receptor subtype, the histamine H1 receptor.
Intestinal malrotation is a major diagnostic challenge in children. Sometimes the prognostic significance of the findings from upper gastrointestinal tract examinations is unclear. In a series of 69 surgically proved cases, the authors studied the prevalence and clinical consequences of various radiographic patterns of malrotation and correlated surgical findings with the radiographic location of the duodenum and cecum. Seven patterns of duodenal malrotation were observed. Almost all children in the series had abnormalities of rotation or fixation of both the duodenum and colon, resulting in narrowing of the mesenteric base with potential for midgut volvulus. Of 69 patients, only one (1.4%) had an anatomically normal duodenum, and four (5.8%) had a surgically confirmed normal cecum fixed in the right lower quadrant. In the absence of a corkscrew or Z-shaped duodenum, patterns that usually indicate volvulus or obstructing Ladd bands, colon position had greater prognostic implication, especially when the cecum was situated in the right upper quadrant or left upper quadrant. These latter patterns were associated with the highest prevalence of volvulus.
PURPOSE: To analyze difficult diagnostic cases of malrotation to identify features crucial to accurate diagnosis. MATERIALS AND METHODS: The authors reviewed the radiographs and records of 81 symptomatic children who underwent surgery with a preoperative diagnosis of malrotation. Eleven had subtle rotational abnormalities (potential false-negative examinations), and 12 had false-positive upper gastrointestinal examinations. RESULTS: Subtle signs of malrotation included unusual redundancy of the duodenum to the right of the spine and location of the duodenojejunal junction (DJJ) medial to the left pedicle. Nevertheless, two children with variations of malrotation had normal upper gastrointestinal examinations. False-positive diagnoses resulted from failure to recognize normal variants: jejunum in the right upper quadrant as the sole finding, DJJ over the left pedicle on the anteroposterior view, "duodenum inversum," and "duodenum mobile." Three children had bowel distention that displaced the DJJ. CONCLUSION: Diagnosis of difficult cases of malrotation may depend on recognition of anatomic subtleties. False-positive diagnoses may be avoided by appreciation of normal duodenal variants.
1. Intracellular recordings were made from neurones in intact guinea-pig nodose ganglia in vitro and from acutely isolated adult guinea-pig and rabbit nodose neurons to study a bradykinin (BK)-mediated block of a slow spike after-hyperpolarization (AHPslow) that is prominent in 30-40% of these neurones. 2. BK (100 nM) reversibly blocked the AHPslow, resulting in an ablation of the spike accommodative properties of these neurones. The B1 BK receptor agonist [des-Arg9]-BK did not mimic or prevent the actions of BK. In contrast, the B2 BK receptor antagonist D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]-BK (HOE 140) prevented BK-induced block of the AHPslow and the effect of BK on spike frequency adaptation. 3. The BK block of the AHPslow in acutely dissociated neurones was prevented by indomethacin, indicating that this BK effect was dependent upon a cyclo-oxygenase metabolite intrinsic to these neurones. 4. One to twenty femtomoles of the prostanoids PGE2, PGD2, 9 alpha, 11 beta-PGF2 (a metabolite of PGD2), PGF2 alpha, TxB2 and PGI2 were released spontaneously from a nodose ganglion in 15 min. BK (100 nM) selectively increased PGI2 release 2.8-fold without affecting the release of the other prostanoids. Treatment with 10 microM tranylcypromine (TCP), a putative PGI2 synthase inhibitor, completely prevented the BK-induced release of PGI2. 5. In the presence of 10 microM TCP, BK no longer produced significant effects on the AHPslow. In contrast, 10 microM TCP did not prevent PGI2 from blocking the AHPslow. 6. These results suggest that vagal afferents that exhibit AHPslow also possess the B2 type of BK receptor. Activation of these BK receptors results in the production of PGI2, which in turn controls spike frequency adaptation by affecting the amplitude of the AHPslow.
The process of bacterial translocation (BT) after ischemia/reperfusion (I/R) injury is reported to be mediated by local mucosal factors, the effects of pancreatic enzymes, epithelial disruption, and by dysfunctional intestinal motility. Octreotide (OCT), a somatostatin analog, has been postulated to protect against BT by influencing one or more of these factors. Twenty-two formula-fed piglets (weight, 3.5 +/- 0.5 kg; age, 20 +/- 5 days) were divided into four groups: control (no drug given; no I/R; n = 6), I/R (no drug given; n = 5), I/R plus low-dose OCT (LD OCT, 0.08 microgram/kg; n = 6), and I/R plus high-dose OCT (HD OCT, 8 micrograms/kg; n = 5). All experimental subjects had nonocclusive mesenteric ischemia induced by reversible pericardial tamponade with mesenteric flow decreased to 25 +/- 5% of baseline for 5 hours followed by 15 +/- 5 hours of reperfusion. Mesenteric lymph nodes (MLN), liver, spleen, blood, and peritoneum were harvested for blind microbial analysis. None of the animals in the control group experienced translocation to the tissues tested. All of the animals in the I/R group experienced BT to the MLN. The subjects in the LD OCT and HD OCT groups experienced BT to the MLN 66% and 80% of the time, respectively. Despite the reported clinical evidence that OCT can protect the intestinal mucosa from injury and increase the clearance of bacteria from the gastrointestinal tract, in this study in which variables other than I/R known to promote bacterial translocation were eliminated, OCT failed to modify or prevent the occurrence of translocation to the MLN after I/R injury.
Approximately 5.5 x 109 g (4.0 x 105) of mercury was discharged into the Carson River Drainage Basin of west-central Nevada during processing of the gold- and silver-rich Comstock ore in the late 1800s. For the past 13 decades, mercury has been redistributed throughout 500 km2 of the basin, and concentrations are some of the highest reported values in North America. This article documents the concentrations of mercury in the air, water, and substrate at both contaminated and noncontaminated sites within the basin and discusses the implications for risk assessment. At contaminated areas, the range of mercury concentrations are as follows: mill tailings, 3-1610 micrograms/g; unfiltered reservoir water, 53-591 ng/l; atmospheric vapor, 2-294 ng/m3. These values are three to five orders of magnitude greater than natural background. In all media at contaminated sites, concentrations are spatially variable, and air and water mercury concentrations vary temporally. The study are in situated in a natural mercuriferous belt, and regional background mercury concentrations in all environmental media are higher than values typically cited for natural background. As a mercury-contaminated site in North America, the Carson River Drainage Basin is unusual for a number of reasons, including its location in a natural mercuriferous belt, high and sustained levels of anthropogenic mercury inputs, long exposure time, aridity of the climate, and the riparian setting in an arid landscape, where biological activity is concentrated in the same areas that contain high levels of mercury in multiple media.
Under experimental conditions, the growth of loblolly pine (Pinus taeda L.) is often responsive to ozone at near-ambient concentrations. However, little is known of the biochemical changes associated with this or other pollutants. Loblolly pine seedlings in open-top chambers were exposed to combinations of ozone (sub-ambient, ambient, or twice-ambient), acidic precipitation (pH 3.8 or pH 5.2) and soil magnesium (0.15 or 0.32 microg g(-1) exchangeable Mg) for three growing seasons. The effects of these treatments were greater in foliage than in stems or roots. The largest treatment effect was a 50% decrease in the starch concentration of current-year foliage from the twice-ambient ozone treatment compared with current-year foliage from the sub-ambient ozone treatment. Responses to ozone were consistent with the hypothesis that ozone-induced growth reductions are associated with depletion of carbohydrate reserves resulting from injury compensation and repair processes or reduced carbon fixation or both. Addition of acidic precipitation, and to a small extent Mg, decreased sugar concentrations of tissues; however, this effect appeared to be mediated by nutrient addition rather than by acidity per se. Given the role of carbohydrates in plant resistance to environmental stress, the sensitivity of carbohydrates to experimental treatments demonstrates the potential for indirect effects of ozone, acidic precipitation, and soil properties on stress resistance. Noncarbohydrate constituents were largely unresponsive to the experimental treatments. These findings imply that tissue carbohydrate analysis may be useful for assessing the impacts of pollutants in forest ecosystems.
Gas exchange of individual attached leaves of soybean, Glycine max (L.) Merr cv Davis, was monitored during exposure to exogenous ethylene (C(2)H(4)) to test the hypothesis that the effects of C(2)H(4) on net photosynthesis (P(N)) and stomatal conductance to H(2)O vapor (g(s)) are direct and not mediated by changes in leaf orientation to light. Leaflets were held perpendicular to incident light in a temperature-controlled cuvette throughout a 5.5 hour exposure to 10 microliters per liter C(2)H(4). Declines in both P(N) and g(s) were evident within 2 hours and became more pronounced throughout the exposure period. In C(2)H(4) treated plants, P(N) and g(s) decreased to 80 and 62%, respectively, of the rates in control plants. Because epinastic movement of the leaflets was prohibited by the cuvette, the observed declines in P(N) and g(s) were a direct effect of C(2)H(4) rather than the result of reduced light interception caused by changing leaf angle.
Height and diameter growth, biomass accumulation and leaf pigment concentrations were measured in loblolly pine (Pinus taeda L.) seedlings grown in soil containing 12 or 35 microg Mg g(-1) and exposed from May to October to subambient, ambient, or twice-ambient ozone (O(3)), and to simulated acidic rain with a pH of either 4.0 or 5.3. At the end of one growing season, height and diameter growth of seedlings exposed to twice-ambient O(3) were not statistically different from those of seedlings exposed to subambient O(3). Biomass of all plant parts was reduced by 7 to 16% in response to increasing O(3) concentration. No statistically significant growth responses to rain chemistry or soil magnesium status were observed, and there were no statistically significant interactive treatment effects. Needle pigment concentrations were not significantly affected by rain chemistry or soil Mg status and there were no visible signs of injury to needles that could be attributed to O(3) stress or Mg deficiency. Concentrations of chlorophyll a and b, and carotenes were 23, 30 and 21% higher (P </= 0.05) respectively, in seedlings exposed to twice-ambient O(3) than in seedlings from the other ozone treatments. There were no interactive treatment effects on needle pigment concentrations.
Enzymes which cleave P-O bonds can be blocked by phosphonate analogues of biological phosphates. alpha-Fluorophosphonates are more electronegative at the bridging carbon than simple methylenephosphonates which improves their use for the study of enzymes. Thus, the beta,gamma-difluoromethylene analogue of ATP is a viable substrate for (2----5)An synthetase which converts it into (2----5)An species having a 5'-beta,gamma-difluoromethylene-trisphosphate. This binds strongly to RNase L but does not activate it. The unsymmetrical Ap4Aases from Artemia and lupin are strongly inhibited by P2,P3-fluoromethylenebisphosphonate- and by P1,P4-dithiophosphate-analogues of diadenosyl-5',5"-P1,P4-tetraphosphate while anomalous, non-regiospecific cleavage of some P2,P3-bridged mimics is observed. Certain such analogues inhibit both platelet aggregation in vitro and arterial blood-clotting in rabbits. Separation of the diastereo-isomers of P1,P4-dithiophosphate analogues of Ap4A is achieved using reverse-phase hplc which provides direct access to beta,gamma-CHF-bridged analogues of ATP with resolved stereochemistry at the CHF centre.
Six new methylenephosphonate analogues of P1P4-bis-(5',5'''-adenosyl) tetraphosphate, Ap4A, having P2-P3 carbon bridges CF2, CCl2 and CH2CH2 or P1-P2 and P3-P4 carbon bridges CF2, CCl2 and CH2CH2 in the tetraphosphate chain, were examined as substrates or inhibitors for two specific Ap4A-degrading enzymes: (asymmetrical) Ap4A hydrolase (EC 3.6.1.17) from yellow-lupin seeds and (symmetrical) Ap4A hydrolase (EC 3.6.1.41) from Escherichia coli. All analogues in which the central oxygen atom was replaced by a stable carbon bridge were hydrolysed by the asymmetrical hydrolase (CF2 greater than CCl2 greater than O greater than CHBr greater than CH2 greater than CH2CH2). As expected, these analogues were not hydrolysed by the symmetrical hydrolase, which was also unable to act on analogues having P1-P2 and P3-P4 carbon bridges.
A total of 13 phosphonate analogues of bis(5'-adenosyl) tetraphosphate (AppppA) have been tested as substrates and inhibitors of the asymmetrically cleaving bis(5'-nucleosidyl) tetraphosphatase (NppppNase) from Artemia and the symmetrically cleaving NppppNase from Escherichia coli. With the Artemia enzyme, the substrate efficiency of beta beta'-substituted compounds decreased with decreasing substituent electronegativity (O greater than CF2 greater than CHF greater than CCl2 greater than CHCl greater than CH2) such that AppCF2ppA and AppCH2ppA were hydrolyzed at 70% and 2.5% of the rate of AppppA, respectively. These compounds were competitive inhibitors of this enzyme with Ki values that generally also decreased with electronegativity from 12 microM for AppCF2ppA to 0.4 microM for AppCH2ppA (Km for AppppA = 33 microM). AppCH = CHppA and AppCH2CH2ppA were neither effective substrates nor inhibitors of the Artemia enzyme. Alpha beta,alpha'beta'-Disubstituted analogues were generally less effective inhibitors with Ki values ranging from 23 microM (ApCH2ppCH2pA) to greater than 1.5 mM (ApCH2CH2ppCH2CH2pA). However, they displayed a low and unexpected rate of symmetrical cleavage by the Artemia enzyme: e.g., ApCHFppCHFpA yielded ApCHFp at 3% of the rate of AppppA breakdown. Both sets of analogues were also competitive inhibitors of the E. coli NppppNase with Ki values ranging from 7 microM (AppCH2ppA) to 250 microM (ApCH2CH2ppCH2CH2pA) (Km for AppppA = 28 microM). The only alpha beta,alpha'beta'-disubstituted analogue to be hydrolyzed by the E. coli enzyme was ApCF2ppCF2pA at 0.2% of the rate of AppppA; however, several of the beta beta'-substituted compounds showed a limited degree of asymmetrical cleavage.(ABSTRACT TRUNCATED AT 250 WORDS)
Serotonin (5-HT) increases impulse activity in visceral afferent C-fibers in vivo. A 5-HT-induced membrane depolarization may partially account for this effect. Here, we examined the potential contribution of an additional mechanism to the 5-HT-mediated increase in impulse activity. Approximately 40% of rabbit visceral C-fiber neurons exhibit a protracted (greater than 3 s) spike afterhyperpolarization (AHPslow) that is a major determinant of repetitive firing properties in these neurons. Intracellular recording methods were applied to rabbit nodose ganglion neurons in vitro to assess whether 5-HT could increase excitability through effects on the AHPslow. Results revealed a concentration-dependent 5-HT-mediated depression of the AHPslow amplitude and duration that was accompanied by decreased accommodation of action potential firing. Experiments with 5-HT receptor antagonists further showed that this autacoid depressed the AHPslow through a different 5-HT receptor subtype than that subserving the 5-HT-induced depolarization. Thus the AHPslow represents a distinct locus where 5-HT can increase the impulse activity of these visceral C-fiber afferents.
The physiological site of ethylene action on CO(2) assimilation was investigated in intact plants of Glycine max L., using a whole-plant, open exposure system equipped witha remotely operated single-leaf cuvette. The objective of the study was met by investigating in control and ethylene-treated plants the (a) synchrony in response of CO(2) assimilation, stomatal conductance to water vapor, and substomatal CO(2) partial pressure; (b) response of CO(2) assimilation as a function of a range of substomatal CO(2) partial pressures; and (c) response of CO(2) assimilation as a function of a range of photon flux densities. After exposure to 410 micromoles per cubic meter of ethylene for 2.0 hours, CO(2) assimilation and stomatal conductance declined in synchrony, while substomatal CO(2) partial pressure remained unchanged until exposure times equaled and exceeded 3.0 hours. Because incipient changes in CO(2) assimilation occurred without a change in the CO(2) partial pressure in the leaf interior, it is concluded that both stomatal physiology and the chloroplast's CO(2) assimilatory capacity were initial sites of ethylene action. After 3.5 hours the effect of ethylene on stomatal conductance and CO(2) assimilation exhibited saturation kinetics, and the effect was substantially more pronounced for stomatal conductance than for CO(2) assimilation. Based on the response of CO(2) assimilation to a range of substomatal CO(2) partial pressures, ethylene did not affect either the CO(2) compensation point or carboxylation efficiency at subsaturating CO(2) partial pressures. Above-ambient supplies of CO(2) did not alleviate the diminished rates of CO(2) assimilation. In partitioning the limitations imposed on CO(2) assimilation in control and ethylene-treated plants, the stomatal component accounted for only 16 and 4%, respectively. The response of CO(2) assimilation to a range of photon flux densities suggests that ethylene reduced apparent quantum yield by nearly 50%. Thus, the pronounced decline in net photosynthetic CO(2) assimilation in the presence of ethylene was due more to a loss in the mesophyll tissue's intrinsic capacity to assimilate CO(2) than to a reduction in stomatal conductance.