In vitro activities of new and conventional antifungal agents against clinical Scedosporium isolates.
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The susceptibilities of 13 clinical isolates of Scedosporium apiospermum and 55 clinical isolates of S. prolificans to new and conventional drugs belonging to three different classes of antifungal agents, the azoles (miconazole, itraconazole, voriconazole, UR-9825, posaconazole), the polyenes (amphotericin B, nystatin and liposomal nystatin), and allylamines (terbinafine), were studied by use of proposed standard M38-P of NCCLS. Low growth-inhibitory antifungal activities were found in vitro for most of the drugs tested against S. prolificans isolates, with the MICs at which 90% of isolates are inhibited (MIC(90)s) being >8 microg/ml; the MIC(90)s of voriconazole and UR-9825, however, were 4 microg/ml. S. apiospermum isolates were more susceptible in vitro, with the highest activity exhibited by voriconazole (MIC(90)s, 0.5 microg/ml), followed by miconazole (MIC(90)s, 1 microg/ml), UR-9825 and posaconazole (MIC(90)s, 2 microg/ml), and itraconazole (MIC(90)s, 4 microg/ml). The MICs of terbinafine, amphotericin B, and the two formulations of nystatin (for which no statistically significant differences in antifungal activities were found for the two species) for S. apiospermum isolates were high. Cross-resistance was observed among all the azoles except posaconazole and among all the polyenes except the lipid formulation. A distribution analysis was performed with the MICs of each drug and for each species. Bimodal and skewed MIC distributions were obtained, and cutoffs indicating the borders of different MIC subpopulations of the distributions were determined on the basis of the normal plot technique. These cutoffs were in many cases reproducible between 48 and 72 h. (+info)
Circadian rhythm in intracellular Cl(-) activity of acutely dissociated neurons of suprachiasmatic nucleus.
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A link between the circadian rhythm and the function of Cl(-)-permeable gamma-aminobutyric acid (GABA) type A (GABA(A)) receptors on suprachiasmatic nucleus (SCN) neurons was studied by measuring intracellular activity of Cl(-) (aCl) at different times during a circadian cycle in SCN neurons acutely dissociated from rat brains. To measure aCl, the voltage-clamp mode of the gramicidin-perforated patch-clamp technique was used, and reversal potential of GABA-induced currents (E(GABA)) was converted to aCl. Measured aCl was significantly higher at around noon (20.1 +/- 1.4 mM) than at three other time zones of a circadian cycle (means ranging from 11.6 to 14.3 mM). Chord conductance of GABA-induced currents showed no circadian changes, indicating a lack of circadian changes in the number or single-channel conductance of GABA(A) receptors. These results suggest that aCl participates in modulating GABA(A) receptor functions on SCN neurons during the circadian rhythm. (+info)
Pathways for internalization and recycling of the chemokine receptor CCR5.
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M-tropic human immunodeficiency virus (HIV-1) strains enter the cell after interaction with their receptors, CD4 and the G-protein-coupled chemokine receptor CCR5. The number of cell surface CCR5 molecules is thought to be important in determining the infection rate for HIV. Cell surface CCR5 is dependent on the rate of receptor internalization and recycling. Internalization of G-protein-coupled receptors after agonist activation is thought to occur either through clathrin-coated pits or through caveolae. In this study, the role of these different pathways was investigated in Chinese hamster ovary cells expressing CCR5 using specific inhibitors. Internalization of CCR5 after chemokine treatment was inhibited by sucrose, indicating a role for the clathrin-coated pit pathway. Activation of CCR5 leads to arrestin-2 movement in the cells, providing further evidence for the involvement of clathrin-coated pits. Nystatin and filipin also affected the rate of internalization of CCR5, indicating a role for caveolae. Using inhibitors of vesicle transport in the cell, it was found that the CCR5 recycling pathway is independent of the Golgi apparatus and late endosomes. Protein synthesis is not involved in receptor recovery. It seems likely that after internalization, CCR5 is directed to early endosomes and subsequently recycled to the cell surface. (+info)
cAMP regulation of Cl(-) and HCO(-)(3) secretion across rat fetal distal lung epithelial cells.
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We isolated and cultured fetal distal lung epithelial (FDLE) cells from 17- to 19-day rat fetuses and assayed for anion secretion in Ussing chambers. With symmetrical Ringer solutions, basal short-circuit currents (I(sc)) and transepithelial resistances were 7.9 +/- 0.5 microA/cm(2) and 1,018 +/- 73 Omega.cm(2), respectively (means +/- SE; n = 12). Apical amiloride (10 microM) inhibited basal I(sc) by approximately 50%. Subsequent addition of forskolin (10 microM) increased I(sc) from 3.9 +/- 0.63 microA/cm(2) to 7.51 +/- 0.2 microA/cm(2) (n = 12). Basolateral bumetanide (100 microM) decreased forskolin-stimulated I(sc) from 7.51 +/- 0.2 microA/cm(2) to 5.62 +/- 0.53, whereas basolateral 4,4'-dinitrostilbene-2,2'-disulfonate (5 mM), an inhibitor of HCO secretion, blocked the remaining I(sc). Forskolin addition evoked currents of similar fractional magnitudes in symmetrical Cl(-)- or HCO(-)(3)-free solutions; however, no response was seen using HCO(-)(3)- and Cl(-)-free solutions. The forskolin-stimulated I(sc) was inhibited by glibenclamide but not apical DIDS. Glibenclamide also blocked forskolin-induced I(sc) across monolayers having nystatin-permeablized basolateral membranes. Immunolocalization studies were consistent with the expression of cystic fibrosis transmembrane conductance regulator (CFTR) protein in FDLE cells. In aggregate, these findings indicate the presence of cAMP-activated Cl(-) and HCO(-)(3) secretion across rat FDLE cells mediated via CFTR. (+info)
Insect midgut K(+) secretion: concerted run-down of apical/basolateral transporters with extra-/intracellular acidity.
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In lepidopteran larvae, three transport mechanisms are involved in the active and electrogenic K(+) secretion that occurs in the epithelial goblet cells of the midgut. These consist of (i) basolateral K(+) channels, allowing K(+) entry from the haemolymph into the cytosol, (ii) apical electrogenic K(+)/2H(+) antiporters, which are responsible for secondary active extrusion of K(+) from the cell into the gut lumen via the goblet cavity and (iii) apical V-ATPase-type proton pumps. The latter energize apical K(+) exit by building up a large, cavity-positive electrical potential that drives the antiporters. Net K(+) secretion (I(K)) can be measured as short-circuit current (I(sc)) across the in vitro midgut mounted in an Ussing chamber. We investigated the influence of protons on the transepithelial I(K) and the partial reactions of the basolateral K(+) permeability (P(K)) and the apical, lumped 'K(+) pump' current (I(P)) at various extra- and intracellular pH values. In particular, we wanted to know whether increased cellular acidity could counteract the reversible dissociation of the V-ATPase into its V(1) and V(o) parts, as occurs in yeast after glucose deprivation and in the midgut of Manduca sexta during starvation or moulting, thus possibly enhancing K(+) transport. When intact epithelia were perfused with high-[K(+)] (32 mmol l(-1)) salines with different pH values, I(K) was reversibly reduced when pH values fell below 6 on either side of the epithelium. Attempts to modify the intracellular pH by pulsing with NH(4)(+) or propionate showed that intracellular acidification caused a reduction in I(K) similar to that obtained in response to application of external protons. Treatment with azide, a well-known inhibitor of the mitochondrial ATP synthase, had the same effect as pulsing with ammonium or propionate with, however, much faster kinetics and higher reversibility. Breakdown of the basolateral or apical barrier using the antibiotic nystatin allowed the intracellular pH to be clamped to that of the saline facing the nystatin-treated epithelial border. Cell acidification achieved by this manipulation led to a reduction in both apical I(P) and basolateral P(K). The transepithelial I(K) showed an approximately half-maximal reduction at external pH values close to 5 in intact tissues, and a similar reduction in I(P) and P(K) values was seen at an intracellular pH of 5 in nystatin-permeabilised epithelia. Thus, the hypothesized V(1)V(o) stabilization by cell acidity is not reflected in the pH-sensitivity of I(P). Moreover, all components that transport K(+) are synchronously inhibited below pH 6. The significance of our findings for the midgut in vivo is discussed. (+info)
Multiple regulatory roles of a novel Saccharomyces cerevisiae protein, encoded by YOL002c, in lipid and phosphate metabolism.
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The yeast open reading frame YOL002c encodes a putative membrane protein. This protein is evolutionarily conserved across species, including humans, although the function of each of these proteins remains unknown. YOL002c is highly expressed in yeast cells that are grown in the presence of saturated fatty acids such as myristate. Furthermore, cells in which the YOL002c gene is disrupted grow poorly on this carbon source. These mutant cells are also resistant to the polyene antibiotic, nystatin. Gene chip analysis on yol002cDelta cells revealed that a variety of genes encoding proteins involved in fatty acid metabolism and in the phosphate signaling pathway are induced in this mutant strain. In addition, our studies demonstrated that in the disruption strain acid phosphatase activity is expressed constitutively, and the cells accumulate polyphosphate to much higher levels than wild-type cells. A homologous human protein is able to partially rescue these defects in phosphate metabolism. We propose that YOL002c encodes a Saccharomyces cerevisiae protein that plays a key role in metabolic pathways that regulate lipid and phosphate metabolism. (+info)
In vitro activity of nystatin compared with those of liposomal nystatin, amphotericin B, and fluconazole against clinical Candida isolates.
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We investigated the in vitro activity of nystatin and liposomal nystatin against 103 Candida isolates to determine the effect of both time and medium on MICs. We also compared the nystatin MICs with those of amphotericin B and fluconazole. Testing was performed in accordance with the National Committee for Clinical Laboratory Standards M27-A microdilution methodology with RPMI 1640, RPMI 1640 supplemented with glucose to 2% (RPMI-2), and antibiotic medium 3 supplemented with glucose to 2% (AM3). While nystatin MICs were similar to or slightly lower than liposomal nystatin MICs in RPMI 1640 and RPMI-2, they were markedly higher than liposomal nystatin MICs in AM3. Use of AM3 and determination of the MIC after 24 h of incubation provided a slightly wider range of liposomal nystatin MICs (0.06 to >16 microg/ml). Under these conditions, the MICs at which 90% of isolates were inhibited of nystatin and liposomal nystatin were 2 and 1 microg/ml, respectively. Nystatin and liposomal nystatin in general showed good activity against all Candida spp. tested. Although the MICs of nystatin and liposomal nystatin tended to rise in parallel with the amphotericin B MICs, nystatin and liposomal nystatin MICs of 1 to 2 and 0.5 to 1 microg/ml, respectively, were obtained for seven and six, respectively, of nine isolates for which amphotericin B MICs were >or=0.25 microg/ml. No correlation between fluconazole and nystatin or liposomal nystatin MICs was observed. As amphotericin B MICs of >or=0.25 microg/ml correlate with in vitro resistance, these results suggest that liposomal nystatin might have activity against some amphotericin B-resistant isolates. In vivo testing in animal models is required for clarification of this issue. (+info)
Hexaene derivatives of nystatin produced as a result of an induced rearrangement within the nysC polyketide synthase gene in S. noursei ATCC 11455.
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Genetic manipulation of the polyketide synthase (PKS) gene nysC involved in the biosynthesis of the tetraene antifungal antibiotic nystatin yielded a recombinant strain producing hexaene nystatin derivatives. Analysis of one such compound, S48HX, by LC-MS/MS suggested that it comprises a 36-membered macrolactone ring completely decorated by the post-PKS modification enzymes. Further characterization by bioassay has shown that S48HX exhibits antifungal activity. Genetic analysis of the hexaene-producing mutant revealed an in-frame deletion within the nysC gene via recombination between two homologous ketoreductase domain-encoding sequences. Apparently, this event resulted in the elimination of one complete module from NysC PKS, subsequently leading to the production of the nystatin derivative with a contracted macrolactone ring. These results represent the first example of manipulation of a PKS gene for the biosynthesis of a polyene antibiotic. (+info)