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Biomedical subjects

R Horn

Publications and source records attributed to R Horn.

At least 109 records · Page 6Linked to original sources
PubMed1991

Diffusion of nystatin in plasma membrane is inhibited by a glass-membrane seal.

In perforated patch recording, the pore former nystatin is incorporated into a cell-attached patch, to increase its conductance. The possibility of lateral diffusion of nystatin through the membrane and under the glass-membrane seal was examined by reversing the nystatin gradient. Namely, a cell-attached patch on a cell was examined while placing nystatin into the bath. The reversal potential and current-voltage relationship of single Ca2+ activated K+ channels in the patch were readily changed by varying the K+ concentration in the bath, showing that nystatin was active in the cell membrane outside of the patch. However, the patch itself did not become leaky. The absence of a conductance induced in the patch by the nystatin in the rest of the plasma membrane of the cell suggests that the lateral diffusion of nystatin is inhibited by the glass-membrane seal.

Biophysical Phenomena↗
PubMed1991

A [Na+]o-independent, pHo-dependent mechanism for reduction of intracellular [Ca2+] after influx through Ca2+ channels in mouse pituitary cells.

The effect of extracellular pH (pHo) on the duration of calcium-dependent chloride currents (ICl(Ca] was studied in voltage clamped AtT-20 pituitary cells. ICl(Ca) was activated by Ca2+ influx through plasma membrane Ca2+ channels, which were opened by step depolarization to voltages between -20 and +60 mV. Increasing pHo from 7.3 to 8.0 reversibly prolonged ICl(Ca) tail currents in perforated patch recordings from cells bathed in both Na(+)-containing and Na(+)-free solutions. This prolongation was prevented in standard whole cell recordings when the pipette solution contained 0.5 mM EGTA. The effects of raised pHo were not due to alteration of intracellular pH, since tail current prolongation still occurred when intracellular pH was buffered at 7.3 with 80 mM HEPES. The prolongation of ICl(Ca) at pHo 8 could not be accounted for by a direct action on Ca2+ channels, since tail currents were prolonged when pHo was changed rapidly during the tail current, after all Ca2+ channels were closed. The effects of increasing pHo on ICl(Ca) also could not be explained by a direct action on Cl- channels, since changing to pHo 8 did not prolong Cl- tail currents when intracellular Ca2+ concentration [( Ca2+]i) was fixed by EGTA in whole cell recordings. Raising pHo did, however, prolong depolarization-evoked [Ca2+]i transients, measured directly with the Ca2+ indicator dye, fura-2. Taken together, these data demonstrate the presence of a Na(+)-independent, pHo-sensitive mechanism for reduction of [Ca2+]i after influx through Ca2+ channels. This mechanism is associated with the plasma membrane, and is active on a time scale that is relevant to the duration of single action potentials in these cells. We suggest that this mechanism is the plasma membrane Ca2+ ATPase.

Action Potentials↗
PubMed1991

Control of action potentials and Ca2+ influx by the Ca(2+)-dependent chloride current in mouse pituitary cells.

1. Perforated patch recording was used to examine the influence of the calcium-dependent chloride current (iCl(Ca)) on Ca2+ action potentials in AtT-20 pituitary cells. The calculated chloride equilibrium potential (ECl) was adjusted by changing either intracellular or extracellular [Cl-]. Action potential duration varied as a function of ECl. When ECl was set at -21 mV, both spontaneous and evoked action potentials displayed a long plateau phase between -20 and -25 mV, which typically lasted for several seconds. Setting ECl to more negative potentials resulted in briefer action potentials; at an ECl of -52 mV, no plateau phase was evident. Spontaneous depolarization and action potential firing still occurred when ECl was negative to firing threshold, which indicates that the slow depolarizing wave that precedes the firing of spontaneous action potentials does not require activation of ICl(Ca). 2. In voltage clamp experiments the magnitude of ICl(Ca) diminished slowly during a prolonged depolarization, over a time course that coincided with action potential termination. 3. Niflumic acid (100 microM) blocked ICl(Ca) by 90% but had no effect on either K+ or Ca2+ currents. This concentration of niflumic acid eliminated the plateau phase, but did not prevent the firing, of Ca2+ action potentials. 4. Internal [Ca2+] was measured photometrically after loading cells with the Ca2+ indicator dye, Fura-2. Under voltage clamp conditions, concentrations of niflumic acid (30-100 microM) that blocked depolarization-evoked ICl(Ca) had little or no effect on simultaneously recorded Ca2+ transients. Perforated patch recording from Fura-loaded cells showed that action potentials were temporally associated with transient increases in intracellular [Ca2+]. Niflumic acid (30-100 microM) disrupted the rhythmic firing of spontaneous action potentials and associated intracellular Ca2+ transients. 5. Fluorescent measurements of Ca2+ transients were also made in cells unperturbed by patch recording, and were used as a measure of action potential duration in the absence of experimental alteration of internal [Cl-]. Spontaneous Ca2+ transients were of long duration (approximately 2 s), which suggests that intracellular [Cl-] is relatively high (40-50 mM) in these cells. The spontaneous Ca2+ transients were inhibited by niflumic acid. 6. Niflumic acid up to 100 microM, had neglible effects on either basal or stimulated (by 2 microM-(+/-)-isoprenaline) hormone secretion, as shown by radioimmunoassay of adrenocortotrophic hormone release.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1991

[Computer-assisted determination of the pharmacokinetic parameters of Solupront after intrauterine administration in cattle].

The drug "Solupront" a sulfonamide was clinical tested in healthy heifers and cows with endometritis, retentio secundinarum etc. The test-results were evaluated with the computer-program "Phakimo". The pharmacokinetic parameters show that there are similar relationships between the extravasal and the intravasal application of this osmochemotherapeutic. A retard of absorption is shown in dioestrus and in prooestrus. If there are pathological signs in uterus, the rate of absorption of the drug is higher and the excretion via urine is more quickly, too. The effect of the sulfonamide in the drug "Solupront" is impaired after application in the uterus in order of the quick absorption, of distribution and excretion and also in order of dilution by lochia and by interaction with p-aminobenzoic acid.

Administration, Intravaginal↗
PubMed1991

[Early results of transversalis-plasty. A prospective randomized comparison of non-resorbable and resorbable sutures].

In a prospective randomized trial we analyzed the perioperative management, complications, and the recurrence rate of inguinal hernia repair using either resorbable (polydioxanone, PDS) or non-absorbable (polyamide, Ethilon) suture material. From January 1988 to June 1989, 484 consecutive transversalis fascia repairs were performed in 425 adult patients with inguinal or femoral hernia. Local anaesthesia was used in 273 cases. At least one year postoperatively, 390 patients with 445 repairs had a clinical follow-up. The recurrence rate after 360 primary herniae was 3.3% (Ethilon 2.3%, PDS 4.3%) while 5.9% rerecurrences were found following operation for recurrent hernia (Ethilon 2.5%, PDS 8.9%). The differences in the recurrence rates following the use of polyamide or polydioxanone were not statistically significant. Complications occurred in 5.2%. The postoperative hospital stay averaged 3.8 days and work was resumed after a mean of 3.9 weeks.

Adolescent↗
PubMed1990

Nordihydroguaiaretic acid inhibits voltage-activated Ca2+ currents independently of lipoxygenase inhibition.

The effects of nordihydroguaiaretic acid (NDGA), a widely used lipoxygenase inhibitor, were examined on voltage-activated Ca2+ channel currents in GH3 and AtT-20 pituitary cells. NDGA (10-100 microM) produced a reversible, dose-dependent inhibition of Ca2+ channel currents, with half-maximal inhibition occurring at 18.6 microM. Inhibition by NDGA developed relatively slowly, did not exhibit use dependence or voltage dependence, and did not require access of NDGA to the extracellular domain of the Ca2+ channel. The maximum inhibition of macroscopic currents by 30 microM NDGA was equivalent in the presence of 5 and 50 mM extracellular Ca2+ and 5 mM Ba2+. NDGA inhibited Ca2+ channel currents in excised, outside-out patches, in the absence of intra- and extracellular Ca2+ (with Ba2+ as the charge carrier), and following preincubation of the cells with the phospholipase A2 inhibitor 4-bromophenacylbromide. Of five other lipoxygenase inhibitors tested, only one inhibited Ca2+ currents. These results suggest that NDGA inhibits Ca2+ channel currents by a mechanism distinct from that of other known Ca2+ channel antagonists and that, when influx of Ca2+ through voltage-gated channels is involved, inhibition of Ca2(+)-dependent cell functions by NDGA (greater than 10 microM) may be independent of effects on arachidonic acid metabolism.

Animals↗
PubMed1990

Phencyclidine blocks voltage-dependent potassium currents in murine thymocytes.

We investigated the effect of phencyclidine (PCP) on the voltage-dependent K+ current in whole cell recordings from murine thymocytes. PCP caused a dramatic, reversible and dose-dependent decrease of the current. An analysis of the dose-response relationship suggests a single site of action for PCP with an IC50 of 4.7 microM. Dextrorphan and naloxone also inhibited the current, although their effects were of a lower magnitude than those of PCP. Neither 10 microM dextrorphan nor 100 microM naloxone antagonized the inhibitory action of 10 microM PCP. The analysis of the dose-response curve for PCP in presence of 100 microM naloxone suggested that the two drugs act at the same site. We also investigated the effect of morphine on the K+ current. Morphine, in concentrations up to 100 microM, inhibited the K+ current less than dextrorphan or PCP. The kinetics and voltage dependence of the currents in the presence of morphine suggest that it interacts with a different site or different conformation of the channel than the other three compounds. Our findings show that certain opioids can act on thymocytes through a system completely different from the typical opioid receptors.

Animals↗
PubMed1989

Postnatal development of lectin binding sites in the rat ventral prostate.

Five Fluorescein-isothiocyanate (FITC)-labelled lectins were used to study the postnatal development of carbohydrate constituents in the rat ventral prostate: Concanavalin A (Con A), wheat germ agglutinin (WGA), peanut agglutinin (PNA), Dolichos biflorus agglutinin (DBA) and Ricinus communis agglutinin I (RCA-I). With all the lectins tested, except RCA-I, specific binding sites could be shown for every stage of differentiation in the glandular epithelium. Binding sites for Con A, WGA, PNA and DBA were found from day 10 to 13 post partum onwards. Each lectin showed a characteristic localization. Binding sites for the lectins used changed to different extents during the following two weeks. After the 24th day post partum no further changes in the lectin binding pattern could be found. The development of the lectin binding properties showed that the changes in carbohydrate-containing constituents of the prostate correlate with the beginning of prostatic secretion and to prostatic epithelial differentiation. In the periacinar stroma the development of the lectin binding pattern was similar to that in the glandular epithelium. The changes of stromal binding sites for Con A and WGA during epithelial differentiation may reflect the changes of epithelial-stromal interactions in the prostate.

Animals↗
PubMed1989

Influence of sodium-calcium exchange on calcium current rundown and the duration of calcium-dependent chloride currents in pituitary cells, studied with whole cell and perforated patch recording.

The whole cell patch-clamp technique, in both standard and perforated patch configurations, was used to study the influence of Na+-Ca++ exchange on rundown of voltage-gated Ca++ currents and on the duration of tail currents mediated by Ca++-dependent Cl- channels. Ca++ currents were studied in GH3 pituitary cells; Ca++-dependent Cl- currents were studied in AtT-20 pituitary cells. Na+-Ca++ exchange was inhibited by substitution of tetraethylammonium (TEA+) or tetramethylammonium (TMA+) for extracellular Na+. Control experiments demonstrated that substitution of TEA+ for Na+ did not produce its effects via a direct interaction with Ca++-dependent Cl- channels or via blockade of Na+-H+ exchange. When studied with standard whole cell methods, Ca++ and Ca++-dependent Cl- currents ran down within 5-20 min. Rundown was accelerated by inhibition of Na+-Ca++ exchange. In contrast, the amplitude of both Ca++ and Ca++-dependent Cl- currents remained stable for 30-150 min when the perforated patch method was used. Inhibition of Na+-Ca++ exchange within the first 30 min of perforated patch recording did not cause rundown. The rate of Ca++-dependent Cl- current deactivation also remained stable for up to 70 min in perforated patch experiments, which suggests that endogenous Ca++ buffering mechanisms remained stable. The duration of Ca++-dependent Cl- currents was positively correlated with the amount of Ca++ influx through voltage-gated Ca++ channels, and was prolonged by inhibition of Na+-Ca++ exchange. The influence of Na+-Ca++ exchange on Cl- currents was greater for larger currents, which were produced by greater influx of Ca++. Regardless of Ca++ influx, however, the prolongation of Cl- tail currents that resulted from inhibition of Na+-Ca++ exchange was modest. Tail currents were prolonged within tens to hundreds of milliseconds of switching from Na+- to TEA+-containing bath solutions. After inhibition of Na+-Ca++ exchange, tail current decay kinetics remained complex. These data strongly suggest that in the intact cell, Na+-Ca++ exchange plays a direct but nonexclusive role in limiting the duration of Ca++-dependent membrane currents. In addition, these studies suggest that the perforated patch technique is a useful method for studying the regulation of functionally relevant Ca++ transients near the cytoplasmic surface of the plasma membrane.

Calcium↗
PubMed1989

Recovery of Mycobacterium avium-M. intracellulare from blood specimens by using the routine BACTEC 6B blood culture system.

We describe a simple technique for recovery of Mycobacterium avium-M. intracellulare from blood culture specimens by using the BACTEC 460, a system used for routine blood cultures in many hospital laboratories. A total of 26 of 215 blood specimens (12%) from 11 of 48 patients (23%) with acquired immunodeficiency syndrome (AIDS) or AIDS-related complex yielded isolates of M. avium-M. intracellulare. Acid-fast staining of prepared specimens was positive for 16 of 26 cultures that ultimately yielded the organism.

Acquired Immunodeficiency Syndrome↗
PubMed1989

[The absorption behavior of chemotherapeutics after intrauterine administration in cattle].

The uterus of cattle is an organ of excellent absorptive properties, as has been demonstrated by the examples of a sulphonamide and of penicillin. This is true for all cyclic phases. Absorption was somewhat delayed, when animals were in di-oestrus or pro-oestrus. A comparison between rates of absorption by clinically intact and pathomorphologically altered uteri showed absorption of Solupront and Ursopen 40,000 to be much faster in cases of disease. Experimental results as well as knowledge so far obtained on protein binding capacity are likely to support the conclusion that in the pathologically altered uterus bacteriostatic effects of sulphonamides are low due to the high amount of p-aminobenzoic acid which is present as a direct antagonist in pus and cellular detritus.

Absorption↗
PubMed1988

The microbiology of multiple organ failure. The proximal gastrointestinal tract as an occult reservoir of pathogens.

The microbiology of infection acquired in the intensive care unit (ICU) was studied prospectively in 205 consecutive patients admitted to a surgical intensive care unit. A multiple organ failure (MOF) score was calculated for each admission. Susceptibility to ICU-acquired infection increased with increasing MOF scores. While Escherichia coli, Bacteroides fragilis, and enterococci were the most common isolates from infections present at the time of ICU admission, Staphylococcus epidermidis, Candida, and Pseudomonas dominated infections occurring in patients with high MOF scores. Mortality correlated highly with infection due to S epidermidis or Candida and only poorly with infection due to Pseudomonas or E coli; significant foci of invasive infection were frequently absent at autopsy. Quantitative cultures of proximal gastrointestinal fluid in 16 of these patients showed Candida, S epidermidis, and Pseudomonas to be the most common isolates, and all but one patient colonized with these organisms had invasive infection with the same organism. The proximal gastrointestinal tract appears to be an important occult reservoir of the predominant pathogens in MOF.

Bacteroides fragilis↗
PubMed1988

HIV-II infection with initial neurological manifestation.

A patient with positive serological HIV-II reactions is presented, who lived for many years in North and West Africa and on the Arabian peninsula, and who developed asthenica, incontinence, gait disturbances, impaired mental function, personality changes and finally spastic paraplegia and peripheral neuropathy. He was shown to have a chronic inflammatory process of the central nervous system with cerebral atrophy.

Acquired Immunodeficiency Syndrome↗