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R Warth

Publications and source records attributed to R Warth.

42 records · Page 3Linked to original sources
PubMed1992

Small-conductance chloride channels induced by cAMP, Ca2+, and hypotonicity in HT29 cells: ion selectivity, additivity and stilbene sensitivity.

Previous studies in HT29 cells utilizing the cell-attached nystatin (CAN) method [Greger R, Kunzelmann K (1991) Pflügers Arch 419:209-211] have revealed that the Cl- channels induced by cAMP or by increasing cytosolic Ca2+, e.g. by addition of ATP, and by hypotonic cell swelling share in common their conductance, which was so small in our studies [Kunzelmann et al. (1992) Pflügers Arch (in press)] that we could not resolve it at the single-channel level. This prompted the question whether these Cl- conductances can be distinguished in terms of their ion selectivity and sensitivity towards inhibitors. Whether these pathways are additive or not was also examined. The present study utilized the whole-cell patch-clamp and the CAN methods. A total of 160 patches were studied. In whole-cell patches 8-(4-chlorophenylthio)-cAMP (cAMP, 0.1 +/- 1 mmol/l) induced a significant depolarization by 5 mV and a twofold increase in conductance (G) from 6.2 +/- 1.5 nS to 11.7 +/- 3.2 nS (n = 15). Total replacement of Cl- by Br- and I- in cAMP-treated cells hyperpolarized the membrane voltage (V) significantly from -35 +/- 2.8 to -39 +/- 3.4 and -45 +/- 3.3 mV respectively, but had no detectable effect on G, which was 11.9 +/- 3.3 nS in the case of Br- and 11.8 +/- 3.3 nS in the case of I-. Hence, the permselectivity of the cAMP pathway was I- > Br- > Cl-, but the conductances for these anions were all indistinguishable.(ABSTRACT TRUNCATED AT 250 WORDS)

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1992

Small-conductance Cl- channels in HT29 cells: activation by Ca2+, hypotonic cell swelling and 8-Br-cGMP.

The present study demonstrates the activation of Cl- channels in HT29 cells by agonist (ATP, neurotensin, carbachol) increasing cytosolic Ca2+, by hypotonic cell swelling and by cGMP. Cell-attached nystatin patch-clamp (CAN) as well as slow and fast whole-cell recordings were used. The cell membrane potential was depolarized in a dose-dependent manner with half-maximal effects at 0.4 mumol/l for ATP, 60 pmol/l for neurotensin and 0.8 mumol/l for carbachol. The depolarization, which was caused by Cl- conductances increases, occurred within 1 s and was accompanied by a simultaneous and reversible increase of the input conductance of the cell-attached membrane from 295 +/- 32 pS to 1180 +/- 271 pS (ATP; 10 mumol/l, n = 21) and 192 +/- 37 pS to 443 +/- 128 pS (neurotensin; 1 nmol/l, n = 8). The effects of the agonists could be mimicked by ionomycin (0.2 mumol/l), suggesting that an increase in intracellular Ca2+ was responsible for the activation of Cl- channels. The depolarization was followed by a secondary hyperpolarization. Hypotonic cell swelling also depolarized the cells and induced an increase in the membrane conductance. With 120 mmol/l NaCl the depolarization was 10 +/- 0.8 mV and the cell-attached conductance increased from 228 +/- 29 pS to 410 +/- 65 (n = 26) pS. NaCl at 90 mmol/l and 72.5 mmol/l had even stronger effects. Comparable conductance increases were also obtained when the different agonists or hypotonic cell swelling were examined in whole cell experiments. 5-Nitro-2-(3-phenylpropylamino)-benzoate (1 mumol/l) did not prevent the effects of Ca(2+)-increasing hormones and of hypotonic solutions.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1982

Peptidoglycan of Rhodopseudomonas viridis: partial lack of N-acetyl substitution of glucosamine.

A lack of at least 70% of N-acetyl substitution of glucosamine in the glycan strands of the peptidoglycan from the gram-negative bacterium Rhodopseudomonas viridis is reported. A disaccharide, very likely GlcN beta(1 leads to 4) Mur, was observed in hydrolysates of the isolated peptidoglycan. The disaccharide was not observed when peptidoglycan was N-acetylated before hydrolysis. The peptidoglycan of R. viridis was resistant to lysozyme but became sensitive after N-acetylation with acetic anhydride. The disaccharide was found with peptidoglycan from all R. viridis strains investigated, as well as with R. sulfoviridis P1 and R. palustris strains, but not with peptidoglycan from R. gelatinosa, Rhodospirillum tenue, and Pseudomonas diminuta NCTC 8545.

Acetylation↗
PubMed1976

A rapid method for dry weight determination of proteins on a micro scale with an electrobalance.

A method to determine the dry weight (0.25-2 mg) of aqueous protein solutions within 1 h, using an electrobalance, is described. The drying of 50-200 mul solution pipetted onto a glass fiber disc is carried out in vacuo at 70 degrees C until the recorded dry weight becomes constant (within 25-40 min). It has been shown that the dried residue can subsequently be used for other purposes, such as quantitative amino acid analyses. The method is also suitable for the determination of moisture content in lyophilized protein samples.

Amino Acids↗
PubMedDate not supplied

Expression and function of colonic epithelial KvLQT1 K+ channels.

1. KvLQT1 (KCNQ1) is a voltage-gated K+ channel essential for repolarization of the heart action potential. Defects in ion channels have been demonstrated in cardiac arrhythmia. This channel is inhibited potently by the chromanol 293B. The same compound has been shown to block cAMP-dependent electrolyte secretion in rat and human colon. Therefore, it was suggested that a K+ channel similar to KvLQT1 is expressed in the colonic epithelium. 2. In the present paper, expression of KvLQT1 and its function in colonic epithelial cells is described. Reverse transcription-polymerase chain reaction analysis of rat colonic mucosa demonstrated expression of KvLQT1 in both crypt cells and surface epithelium. When expressed in Xenopus oocytes, KvLQT1 induced a typical delayed activated K+ current. 3. As demonstrated, the channel activity could be further activated by increases in intracellular cAMP. These and other data support the concept that KvLQT1 is forming a component of the basolateral cAMP-activated K+ conductance in the colonic epithelium.

1-Methyl-3-isobutylxanthine↗