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Biomedical subjects

W Simon

Publications and source records attributed to W Simon.

At least 37 records · Page 2Linked to original sources
PubMed1989

Intracellular magnesium ion selective microelectrode based on a neutral carrier.

A magnesium ion selective microelectrode based on a synthetic neutral carrier is presented. The selectivity of Mg2+ over Na+, K+, H+, and Ca2+ is sufficient for assays of intracellular magnesium ion activities. The microelectrodes with an optimized membrane composition have a resistance of about 5 x 10(10) omega and a 90% response time of less than or equal to 3 s for a tip diameter around 1 microns. The lifetime of the microelectrode cell assembly is longer than 1 week and the emf drift after equilibration is less than or equal to 0.3 mV/h.

Animals↗
PubMed1989

A new double-barrelled, ionophore-based microelectrode for chloride ions.

A new Cl- selective microelectrode based on the ionophore 5,10,15,20-tetraphenyl-21H,23H-porphin manganese(III) chloride is presented which discriminates better against HCO3- and several organic anions than electrodes containing the Corning 477913 ion-exchanger. Using a redesigned construction procedure, fine-tip double-barrelled microelectrodes were produced which had slopes of -52.4 +/- 0.6 mV (SE, n = 24), resistances of about 7.10(11) omega and a selectivity coefficient log KpotCLHCO3 of -1.40 +/- 0.03. Some electrodes showed a small unexplained sensitivity to pH greater than 7.6. When used to puncture cells of isolated S3 segments of rabbit renal proximal tubule during perfusion with HCO3- Ringer solution, the electrodes gave a membrane potential of -69.8 +/- 1.5 mV and an intracellular Cl- activity, [Cl-]i, of 35.3 +/- 2.6 mmol/l. Upon switching bath and lumen perfusions to Cl- -free solutions the "residual" [Cl-]i dropped to 1.20 +/- 0.03 mmol/l, while in similar measurements with ion-exchanger electrodes the "residual" [Cl-]i dropped only to 10.9 +/- 0.5 mmol/l. These observations demonstrate the superiority of the new electrode and prove that previously determined high [Cl-]i values in Cl- -free ambient solutions reflect interference problems rather than non-exchangeable intracellular chloride.

Animals↗
PubMed1988

Extra- and intracellular hydrogen ion-selective microelectrode based on neutral carriers with extended pH response range in acid media.

A series of new neutral hydrogen ion carriers suitable for application in H+-selective microelectrodes is presented. One carrier (ETH 1907) proves to be superior to tridodecylamine currently very much in use. Microelectrodes based on ETH 1907 in an optimized membrane composition exhibit a linear dynamic response function from pH 2 to 9 extended into the acidic range, a response time less than or equal to 5 s, and a resistance of about 35 G omega for a tip diameter of about 1 micron. This makes the electrode suitable for measurements at normal physiological intracellular pH as well as in acid physiological media. Measurements using this microelectrode in proximal tubule cells of isolated perfused frog kidney are presented.

Animals↗
PubMed1988

NH4+ ion-selective microelectrode based on the antibiotics nonactin/monactin.

A liquid-membrane microelectrode (less than or equal to 1 micron tip diameter) using macrotetrolide antibiotics as ion-selective components is described. The electrode shows selectivities of NH4+ over K+, Na+ and H+ of 3.8, 100 and 150, respectively. The stability and reproducibility of the sensor signal and the response time are determined in solutions with a typical intracellular ion background. The microelectrode does not suffer from significant interference by inorganic and organic inhibitors and lipophilic cations, but high concentrations of lipophilic anions may interfere considerably.

Anti-Bacterial Agents↗
PubMed1988

Upper and lower time limits in the decision to recommend marrow transplantation for patients with chronic myelogenous leukaemia.

Long-term survival of patients with chronic myelogenous leukaemia (CML) requires marrow transplantation from a histocompatible donor. The optimal timing of the transplant is difficult to determine because of the high peritransplant mortality of 20-35% and the existence of a group of patients who can have the disease controlled by drug treatment for prolonged periods. We have developed a mathematical model implemented with a computer program which calculates lower and upper time limits for the timing of marrow transplantation. The lower time limit for transplantation is derived from the loss of life expectancy with delay, and the upper time limit is calculated by comparing the transplant survival probability with the probability of surviving an additional year without a transplant. Thus, an objective basis is provided for bracketing the most appropriate time for transplantation. This analysis suggests that the decision to transplant can be postponed in some patients for periods longer than may generally be recommended.

Adult↗
PubMed1987

Valinomycin-based K+ selective microelectrodes with low electrical membrane resistance.

A valinomycin-based membrane phase for microelectrodes with relatively low electrical membrane resistances is described. Microelectrodes with tip diameters of about 1 micron exhibit resistances of about 10(10) omega. Extremely high K+ selectivities are obtained, e.g. a rejection of Na+ by a factor of 5000 and of acetylcholine by a factor of 3400. At a constant background of 140 and 500 mM Na+, the detection limit of the K+ sensor is at 1.6 X 10(-5) and at 2.5 X 10(-5) M K+, respectively.

Electric Conductivity↗
PubMed1987

Intracellular neutral carrier-based Ca2+ microelectrode with subnanomolar detection limit.

In intracellular electrolyte solutions a Ca2+-selective microelectrode based on the synthetic electrically neutral carrier N,N,N',N'-tetracyclohexyl-3-oxapentanediamide (ETH 129) shows an improved detection limit when compared with the so far widely used Ca2+ microelectrodes based on the neutral carrier ETH 1001. Detection limits are found at pCa = 9.2 in Ca2+ buffers containing an intracellular background of K+ (125 mM). Selectivity studies in mixed solutions show a preference of Ca2+ over Na+ of 6 X 10(5), over K+ of 1.6 X 10(6), and over Mg2+ of 5 X 10(6). The microelectrode does not suffer from significant interference by inorganic and organic inhibitors and by lipophilic cations and anions. The low detection limit is unchanged at least during the first eight hours of continuous contact with Ca2+ solutions. The EMF drift during the first hour of use is between 5 and 10 mV and is then reduced to about 1 mV/h. The changes in EMF induced between solution of pCa = 7 and pCa = 8 are reproducible within 24.7 +/- 0.4 mV (SD, n = 8, about 3 h). These electrode characteristics were found for single-barrelled microelectrodes of one micrometer diameter front-filled with a PVC-containing membrane phase. In the absence of poly(vinyl chloride) in the membrane phase irregular EMF response curves were obtained throughout. Preliminary punctures of ferret ventricular muscle cells indicate that the Ca2+ electrode response is not disturbed by the contact of a cytosolic milieu.

Animals↗
PubMed1987

The sexual scripting of oral genital contacts.

There is evidence from a number of sources that contemporary cultural scenarios for sexual conduct are often very approving of oral genital sex. Two surveys of sexual conduct are analyzed to examine the changes in interpersonal sexual scripts for oral genital sex for cohorts of white and college-educated young people who entered young adulthood between 1928 and 1943 and 1963 to 1967. Males in the earlier cohort had an excess of fellatio during the premarital period from erotic contacts with prostitutes and transient partners. In contacts with potential marital partners and in marriage men and women had equivalent rates of oral sex indicating a greater sexual reciprocity in these affectional relationships. In the latter cohort male and female rates of oral sex before marriage are substantially greater than for the earlier period but are equivalent for the two genders. In both periods oral sex is most common among the coitally experienced and is initiated by males. Evidence is found for an increased amount of sexual activity unlinked to marriage, what might be labeled pre-premarital sex. Male participation in oral sex seems responsive to opportunity, lowered moral inhibition, and emotional commitment while females' participation seems more linked to features of the ongoing relationship. In a review of studies in the 1970s and 1980s a further major increase in the incidence of oral sex in the period before marriage can be found. From these data it appears that oral sex has become, over the last 50 years, part of the sexual scripts of many young people and is a common, though not necessarily a frequent, component of sexual relations in contemporary marriage.

Adolescent↗
PubMed1987

Design of ionophores for ion-selective microsensors.

Requirements for a reliable use of liquid membrane microelectrodes are discussed in terms of stability, response time, and lifetime on the basis of membrane technological considerations. The selectivity of H+, Li+, Na+, K+, Mg2+, Ca2+, and Cl- microelectrodes is critically evaluated using the Nikolskii-Eisenman formalism. Recent progress in the design of new ionophores is presented. A novel neutral carrier-based Ca2+-selective microelectrode with a detection limit of about 5 X 10(-10) M Ca2+ at a background of 125 mM K+ has been realized. An neutral carrier-based microelectrode for H+ with extended pH range of the sample solution is now available. Promising developments in the field of Li+-, Mg2+-, and Cl--selective ionophores are discussed.

Animals↗
PubMed1987

Cell contamination due to the use of carrier-based microelectrodes.

When using microelectrodes for intracellular ion activity studies, some uncertainties such as interference from cytosolic components at the microelectrode, cell damage, and cell contamination may arise. A model, which treats kinetic processes of the loss of carriers from the membrane phase of microelectrodes into the cytosol and cell membrane, is used for an estimation of the extent and time course of contamination by impaled ion-selective microelectrodes. An isolated model cell consisting of a plasma membrane surrounding a cytosolic milieu is assumed. The results of its considerations represent a worst case situation, in which significant contamination of the cell membrane of such a small isolated single cell might occur during time periods of electrophysiological experiments. In more complex situations, such as in intact tissues, the equilibrium membrane concentrations may be substantially less.

Animals↗