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W J Lucas

Publications and source records attributed to W J Lucas.

90 records · Page 5Linked to original sources
PubMed1981

Influence of Turgor Pressure Manipulation on Plasmalemma Transport of HCO(3) and OH in Chara corallina.

A modified version of the osmotic shock technique was used to investigate HCO(3) (-) and OH(-) transport in the alga Chara corallina. Cell turgor was brought close to zero and then restored. When turgor was reduced to near the plasmolytic point using an osmoticum, little effect was observed on H(14)CO(3) (-) assimilation and OH(-) transport. However, when turgor was recovered in these cells, there was a large reduction in HCO(3) (-) and OH(-) transport activity. In contrast, when cells were air-dried to zero turgor, and rewetted to restore turgor, no significant effect on OH(-) transport was observed.The effect of plasmolysis was also studied. When Chara cells were plasmolyzed, in most cases, all OH(-) transport activity was lost and acidification was observed along the cell surface.None of the above treatments had any long term effect on cyclosis. These results are discussed with respect to present concepts of turgorinduced changes in membrane functions.

Journal Article↗
PubMed1981

Effect of Sulfhydryl Reagents on the Biophysical Properties of the Plasmalemma of Chara corallina.

The administration of the sulfhydryl reagent N-ethyl-maleimide (NEM) to internodal cells of Chara corallina caused alterations in the biophysical properties of the plasmalemma, as measured with electrophysiological and radioactive tracer techniques. The membrane potential depolarized to, or near, the calculated Nernst potential for potassium (E(K)) after 30 seconds' exposure to 0.1 millimolar NEM. During this time, the ATP level did not decrease below the control value, and the specific membrane resistance did not increase; only upon further exposure to NEM did the resistance approach the value observed in the dark. In the depolarized state, the membrane potential responded to changes in the external potassium concentration in the manner of a K(+)-electrode, but it retained it's relative insensitivity to external sodium.THESE RESULTS ARE INTERPRETED IN THE FOLLOWING MANNER: NEM causes a) an increase in the membrane permeability to K(+) (i.e. an increase in K(+) conductance); and b) perturbation of the electrogenic transport system(s) of the plasma membrane. The latter effect is manifested in a manner that is not consistent with an inhibition of ATP catalysis by a voltage-dependent ATPase possessing conductance. The nonpermeant sulfhydryl modifier, p-chloromercuribenzenesulfonic acid, appeared to affect membrane properties in a similar, but reversible, way.

Journal Article↗
PubMed1980

Facilitated ultracytochemical demonstration of retrograde axonal transport of horseradish peroxidase in peripheral nerve.

p-Phenylenediamine/pyrocatechol mixture (PPD-PC) was evaluated as a reagent for the ultracytochemical demonstration of retrograde axonal transport of horseradish peroxidase (HRP). HRP crystals were applied to the proximal stumps of the severed infraorbital nerves in rats. After 48 h the rats were sacrificed by perfusion, and the trigeminal ganglia ipsilateral to the severed nerves were processed for HRP cytochemistry and then prepared for electron microscopy. PPD-PC was rapidly oxidized in HRP-labeled neurons to form a dark brown-black osmiophilic reaction product which was more readily visible than the DAB product in the sections. This facilitated selection by light microscopy of areas in the epoxy wafers for ultrathin sectioning. In thin sections viewed under the electron microscope, the osmicated electron opaque PPD-PC reaction product was present in membrane-bound structures including smooth endoplasmic reticulum and granules of various sizes. The PPD-PC reaction product formed after 10-min incubation appeared to be more electron opaque than the DAB reaction product formed after 20 min. PPD-PC was found to be much less readily oxidized than DAB by endogenous hemoproteins. This methodology facilitated the ultracytochemical localization of HRP in neurons following retrograde axonal transport.

3,3'-Diaminobenzidine↗
PubMed1980

Sulfhydryl Group Involvement in Plasmalemma Transport of HCO(3) and OH in Chara corallina.

The effect of the sulfhydryl reagents (-SH) p-chloromercuribenzene-sulfonic acid (PCMBS), N-ethylmaleimide (NEM), and inorganic mercury on H(14)CO(3) (-) assimilation in Chara corallina is reported. Commercial grade PCMBS caused severe inhibition of H(14)CO(3) (-) assimilation. Results obtained using purified PCMBS (stock solution passed through a chelating resin) indicated that inhibition observed using unpurified PCMBS was due predominantly to the presence of inorganic mercury (as a contaminant). The inhibitory role of inorganic mercury was verified using HgCl(2). This chemical caused a dramatic inhibition of H(14)CO(3) (-) assimilation, while it had little effect on cellular (14)CO(2) fixation. Reversal of the Hg(2+) inhibition of H(14)CO(3) (-) assimilation (in presence of 1.0 millimolar dithioerythritol) was extremely slow, requiring 2 to 3 hours for the reestablishment of control rates. This slow recovery may reflect de novo synthesis of transport proteins.Almost complete (irreversible) inhibition of H(14)CO(3) (-) assimilation was observed after cells were briefly (2 min) exposed to 0.1 to 0.3 millimolar NEM. At critical concentrations, both inorganic mercury and NEM perturbed the HCO(3) (-) transport system to such an extent that the H(14)CO(3) (-) assimilation versus HCO(3) concentration profiles changed shape. This could reflect a conversion of the transport system to a facilitated diffusion mode. Alternatively, the efficiency of the transport system may have been affected such that HCO(3) (-) efflux increased significantly.The influence of these -SH reagents on the OH(-) efflux system was also investigated. The H(14)CO(3) (-) assimilation and OH(-) efflux results demonstrate the involvement of -SH groups in the plasmalemma transport of both HCO(3) (-) and OH(-) in C. corallina. Greater transport susceptibility to inorganic mercury and NEM compared to purified PCMBS suggested that the sulfhydryl groups were not located on the peripheral surface of the plasmalemma.

Journal Article↗
PubMed1980

Plasmalemma Transport of OH in Chara corallina: III. FURTHER STUDIES ON TRANSPORT SUBSTRATE AND DIRECTIONALITY.

The identity of the plasmalemma-transported species that develops the alkaline bands of Chara corallina was investigated. The effect of fusicoccin on the rate of HCO(3) (-) assimilation, and on the time-dependent alkaline band pH buildup following low pH flushing, was found to be small, with no stimulatory effect. Computer simulation of the flushing experiments showed that in the experimental situation the alkaline band transport system was slowed down, rather than speeded up, by low pH flushing. A detailed theoretical examination of the maximum rate of proton production from water showed that measured alkaline band fluxes are too large to be explicable in terms of an H(+) influx system. The experimental and theoretical results indicate that the plasmalemma transport of OH(-) ions is responsible for the measured negative external electric potential and alkalinity flux which are associated with the alkaline band phenomenon. Consequently, HCO(3) (-) influx across the characean plasmalemma must be charge-balanced by the efflux of OH(-) ions.

Journal Article↗
PubMed1979

Alkaline Band Formation in Chara corallina: Due to OH Efflux or H Influx?

The nature of the transport system responsible for the establishment of alkaline bands on cells of Chara corallina was investigated. The transport process was found to be insensitive to external pH, provided the value was above a certain threshold. At this threshold (pH 5.1 to 4.8) the transport process was inactivated. Transport function could be recovered by raising the pH value of the external solution. The fastest rate of recovery was always obtained in the presence of exogenous HCO(3) (-).Experiments in which plasmalemma integrity was modified using 10 millimolar K(+) treatment were also performed. Alkaline band transport was significantly reduced in the presence of 10 millimolar K(+), but the system did not recover, following return to 0.2 millimolar K(+) solutions, until the transport site was reexposed to exogenous HCO(3) (-).The influence of presence and absence of various cations on both alkaline band transport and total H(14)CO(3) (-) assimilation was examined. No specific cation requirement (mono- or divalent) was found for either process, except the previously established role of Ca(2+) at the HCO(3) (-) transport site. The alkaline band transport process exhibited a general requirement for cations. This transport system could be partially or completely stalled in low cation solutions, or glass-distilled water, respectively. The results indicate that no cationic flux occurs across the plasmalemma in direct association with either the alkaline band or HCO(3) (-) transport systems.It is felt that the present results offer support for the hypothesis that an OH(-) efflux transport system (rather than a H(+) influx system) is responsible for alkaline band development in C. corallina. The results support the hypothesis that OH(-) efflux is an electrogenic process. This OH(-) transport system also appears to contain two allosteric effector sites, involving an acidic group and a HCO(3) (-) ion.

Journal Article↗
PubMed1978

HCO(3) Influx across the Plasmalemma of Chara corallina: Physiological and Biophysical Influence of 10 mm K.

The effect of 10 mm K(+) on the HCO(3) (-) influx in Chara corallina has been used to distinguish a Ca(2+)-dependent membrane integrity site from the HCO(3) (-) transport site which is also Ca(2+)-dependent (Lucas and Dainty, Plant Physiology 1977 60: 862-867).In the presence of 0.2 mm Ca(2+) at pH 9, 10 mm K(+) inhibits the HCO(3) (-) influx and depolarizes the membrane potential. Inhibition of the HCO(3) (-) influx may be prevented by raising the Ca(2+) concentration in the solution or by addition of Mg(2+), Sr(2+), or Mn(2+). Protection is also afforded by 20 mm Na(+) and Cs(+) but not by Rb(+) which acts as a weak analog of K(+) in producing inhibition of the HCO(3) (-) influx and depolarization of the membrane potential. With the exception of Na(+), ions which prevent inhibition of the influx also prevent depolarization of the membrane potential.Once inhibited by 10 mm K(+), HCO(3) (-) transport cannot be restored by addition of Ca(2+), Mg(2+), or Sr(2+) in less than 3 hours. Addition of Mn(2+), however, results in a progressive restoration of the proportion of cells with influxes equal to the control value. Mn(2+) also produces an increase in the membrane potential with a sharp hyperpolarization occurring at a threshold of about-180 mv. This sudden recovery of the HCO(3) (-) influx in individual cells contrasts with the gradual recovery observed when the K(+) concentration is reduced to 0.2 mm. Since Mn(2+) cannot substitute for Ca(2+) at the HCO(3) (-) transport site, restoration of HCO(3) (-) transport by Mn(2+) involving the membrane integrity site, as evidenced by the effect on the membrane potential and resistance, is clearly separate. The other divalent cations were able to restore HCO(3) (-) transport if applied at a concentration of 2 mm for 14 hours.The OH(-) efflux is also inhibited by 10 mm KCl. It is postulated that voltage dependency of the OH(-) or HCO(3) (-) transport systems may account for the observed effects of 10 mm K(+) on the HCO(3) (-) influx.

Journal Article↗
PubMed1977

Plasmalemma transport of OH- in Chara corallina: dynamics of activation and deactivation.

The light-mediated, time-dependent rise in the pH value at the center of an alkaline band was analyzed using the methods of numerical analysis. From this analysis an expression of the time-dependent build-up of OH- efflux was obtained for these bands. This information can now be employed to determine whether the light-activated transport of OH- and HCO3- influences the electrical properties of the plasmalemma. The dark-induced deactivation of OH- transport was also characterized, revealing a transition from efflux to a transient influx phase during deactivation. Numerical analysis of the steady-state OH- diffusion pattern, established along the surface of an alkaline band, revealed that the OH- efflux width was wider than previously envisaged. It was also found the OH- sink regions exist on either side of the efflux zone. These, and other characteristics revealed by the numerical analysis, enabled us to extend the OH- transport model proposed by Lucas (J. Exp. Bot. 1975, 26:347).

Biological Transport, Active↗
PubMed1977

HCO(3) Influx Across the Plasmalemma of Chara corallina: Divalent Cation Requirement.

An absolute requirement for divalent cations is reported for H(14)CO(3) (-) influx in Chara corallina. Effective substitution of eluted Ca(2+) by Mg(2+) and Sr(2+) was observed, but Mn(2+) was completely ineffective in restoring H(14)CO(3) (-) transport activity. Similarly, La(3+) could not substitute for Ca(2+) in this system. Low concentrations of ethylenediaminetetraacetate (0.01 to 0.06 mm) significantly enhanced the rate at which H(14)CO(3) (-) transport capacity was lost.Examination of the response of OH(-) efflux, during Ca(2+)-free treatment, indicated that the cellular control over OH(-) efflux remained unaffected until membrane integrity became severely affected. This conclusion was supported by the response of OH(-) efflux to 10 mm K(+). Therefore, assimilation of H(14)CO(3) (-) is not rate-limited by an effect of Ca(2+) elution on the OH(-) transport system. Kinetic experiments indicated that Ca(2+) removal from the membrane resulted in noncompetitive inhibition of H(14)CO(3) (-) assimilation; the apparent Michaelis constant remained unaltered over a wide range of conditions. An hypothesis is presented which suggests that membrane integrity is necessary for HCO(3) (-) transport to occur, but Ca(2+) (Mg(2+), Sr(2+)), per se, must be bound to the transport complex before activity is established.

Journal Article↗
PubMedDate not supplied

The physiological effects of supplemental oxygen versus nitrous oxide/oxygen during conscious sedation of pediatric dental patients.

PURPOSE: This study was performed to compare the effects of nitrous oxide/oxygen (N2O/O2) versus oxygen (O2) as adjuncts to an oral narcotic regimen for pediatric conscious sedation. METHODS: Using a randomized double-blind crossover design, 19 children (mean age 41 +/- 8.6 months) were sedated with chloral hydrate (50 mg/kg), meperidine (1.5 mg/kg) and hydroxyzine pamoate (25 mg) for two appointments. Patients were assigned randomly to receive 100% O2 at one visit and 50% N2O/O2 at the other. Physiologic parameters were measured in five-minute intervals, including respiratory rate, pulse rate (PR), oxyhemoglobin saturation (SpO2) and end-tidal carbon dioxide. Data analyses focused on true desaturations and apnea, level of sedation and sedation outcomes. RESULTS: There were no differences in PR, SpO2 and risk of desaturation between the inhalation agents. The level of sedation was deeper and the sedation outcomes were better in the N2O/O2 group. CONCLUSION: N2O/O2 deepened the sedation while improving its success with minimal alteration in physiologic parameters.

Anesthesia, Dental↗
PubMedDate not supplied

A comparison of conventional versus electronic monitoring of sedated pediatric dental patients.

The first purpose of this study was to compare traditional monitoring methods to electronic instruments for monitoring physiologic parameters during conscious sedation of pediatric dental patients. Traditional methods included careful visual assessment of skin color, airway patency and chest movements, and auscultation of breath and heart sounds using a precordial stethoscope; electronic instruments included the capnograph and pulse oximeter. The second purpose of the study was to examine the potential of the capnograph to provide more advanced warning than the pulse oximeter for respiratory compromise. Thirty-nine children (mean age 39 months) received an oral sedative regimen of chloral hydrate, hydroxyzine pamoate, and meperidine and all were supplemented with 100% oxygen via nasal cannula throughout their sedations. One investigator used traditional monitoring and the other used electronic--both monitored simultaneously while being shielded (blinded) from each other. Electronic monitoring yielded a false alert rate of 88% compared with 73% for traditional monitoring. Ten confirmed episodes of respiratory compromise were identified electronically and only three were identified by traditional monitoring. All of the 10 confirmed respiratory compromise episodes were detected by capnography; none were detected by oximetry. During these 39 pediatric sedations using a narcotic drug regimen and 100% oxygen supplementation, there were no true desaturations.

Anesthesia, Dental↗
PubMedDate not supplied

The effect of supplemental oxygen on apnea and oxygen saturation during pediatric conscious sedation.

PURPOSE: This study compared the effect of supplemental oxygen (O2) on pediatric patients' apnea status and oxyhemoglobin saturation during: 1) conscious sedation for dental procedures and 2) the recovery period following sedation. METHODS: Fourteen child patients (mean age 42 months) sedated with 50 mg/Kg chloral hydrate, 25 mg hydroxyzine pamoate, and 1.5 mg/Kg meperidine were treated for two separate appointments. The patients received supplemental O2 via nasal cannulae at random at one of the two appointments. Following the operative period, all patients were monitored sitting upright for an additional 15 min. RESULTS: Intraoperative results showed that the risk of apnea was 39% (11/28), with apneic events distributed equally between O2 and non-O2 supplemented sedations. The overall risk of desaturation was 29% (8/28). Mean SpO2 was always elevated with O2 supplementation and the mean difference in O2 versus non-O2 was statistically significant. The risk of apnea in the postoperative period was 7% (1/14) for both the non-O2 and O2-supplemented patients. The risk of desaturation in the postoperative period was 11% (3/28) with one desaturation in a non-O2 and two desaturations in O2-supplemented patients. CONCLUSION: We conclude that intraoperative O2 supplementation prevents desaturations even in the presence of apnea during pediatric conscious sedation.

Adjuvants, Anesthesia↗