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F Friedrich

Publications and source records attributed to F Friedrich.

At least 37 records · Page 2Linked to original sources
PubMed1995

Genomic characterization of type 3 polioviruses isolated from vaccine-associated poliomyelitis cases in Brazil.

Eight strains of P3/Sabin-related polioviruses were analyzed; four from persistent paralytic poliomyelitis cases classified as vaccine associated, one from a transient paralysis case classified as transverse myelitis, one from a transient paralysis case classified as Guillain-Barré syndrome, one from a transient facial paralysis case, and one from a healthy vaccine. The serotypes of the viral isolates were identified by the neutralization test with hyperimmune equine sera and the relationship of the isolates with the P3/Sabin strain was demonstrated by molecular hybridization of the viral RNA of the isolates with a P3/Sabin-specific probe. The P3/Sabin relationship was confirmed by PCR, using a pair of specific primers for P3/Sabin-related isolates. The available data indicate that a U-->C mutation at nucleotide 472 in the 5' noncoding region of the genome of the type 3 Sabin strain increases the neurovirulence of this strain and this mutation was observed in all type 3 isolates from vaccine-associated cases. These eight P3/Sabin-related isolates were partially sequenced in the 5' noncoding region and seven presented a U-->C mutation at nucleotide 472, except the isolate from a transient paralysis case classified as transverse myelitis, that maintained a U at nucleotide 472. Although this virus maintaining U at nucleotide 472 may not be the etiological agent of the disease, the possibility that the virus was the causative agent of the disease could not be ruled out.

Base Sequence↗
PubMed1995

Genomic characterization of type 2 polioviruses isolated from vaccine-associated cases in Brazil.

Twenty strains of P2/Sabin-related polioviruses isolated in Brazil were analyzed; ten from persistent paralytic poliomyelitis cases, three from suspected polio cases with transient paralysis, and seven from healthy contacts. The serotypes of the viral isolates were identified by the neutralization test with hyperimmune equine sera. The relationship of the isolates to the P2/Sabin strain was demonstrated by molecular hybridization and polymerase chain reaction (PCR). Partial sequencing demonstrated mutations at nucleotide 481 in the 5' noncoding region and at amino acid 143 of the capsid protein VP1 in most of these isolates from vaccine-associated cases in Brazil. These data support previous studies on the importance of mutations at these attenuated determinants in the establishment of the disease. However, the existence of isolates without mutations at these positions suggests that they are not essential. The results also strengthen the possibility of the participation of a mutation at nucleotide 398 in the establishment of the disease, and suggest that a mutation at nucleotide 491 or 500 may also be involved in this process. The isolates from healthy contacts presented the same mutations as the isolates from vaccine-associated cases with which they were in contact. This strengthens the observation that, although mutations in the genome of the P2/Sabin strain are important for the establishment of the disease, host factors are also involved.

Base Sequence↗
PubMed1993

Effect of cell volume on Acridine Orange fluorescence in hepatocytes.

Hepatic proteolysis is inhibited by cell swelling following a variety of experimental manoeuvres, such as reduction of extracellular osmolarity, concentrative uptake of amino acids, or blockade of K+ channels by barium. On the other hand, proteolysis is known to be accomplished by pH-sensitive lysosomal proteases. Accordingly, NH3/NH4+ inhibits proteolysis by intralysosomal alkalinization. The present study has been performed to test for an effect of cell volume on the pH of acidic intracellular compartments, as assessed by Acridine Orange fluorescence at > 520 nm (F > 520). F > 520 is enhanced by NH3/NH4+ (2 and 20 mmol/l respectively), by glutamine (2 mmol/l), by the K(+)-channel blocker barium (10 mmol/l) and by reduction of extracellular osmolarity (by 20 and 80 mosmol/l respectively). The observations point to release of Acridine Orange from acidic cellular compartments, which is indicative of alkalinization of these compartments during cell swelling. This effect may contribute to the regulation of proteolysis.

Acridine Orange↗
PubMed1992

Cell membrane potential oscillations induced by kinins in fibroblasts expressing the Ha-ras oncogene.

In NIH-3T3 fibroblasts expressing the ras oncogene (+ras) bradykinin (BK) elicits sustained oscillations (1/min) of cell membrane potential (PD) due to oscillations of intracellular calcium activity with subsequent activation of calcium sensitive K+ channels. In NIH-3T3 fibroblasts not expressing the oncogene (-ras), BK leads to a single transient hyperpolarization of the cell membrane, not followed by oscillations. The oscillations of cell membrane potential require the presence of extracellular calcium and are abolished by K+ channel blocker barium (1 mmol/l), as well as by calcium channel blockers cadmium (1 mmol/l), lanthanum (0.1 mmol/l) and nifedipine (10 mumol/l). However, the oscillations are not modified by 1 mumol/l nifedipine, or by other calcium channel blockers, such as verapamil (10 mumol/l) or diltiazem (10 mumol/l). Cell proliferation is inhibited by nifedipine (10 mumol/l) but not by verapamil or diltiazem, indicating that the oscillations of intracellular calcium are a prerequisite for the growth factor independent proliferation of ras oncogene expressing cells.

3T3 Cells↗
PubMed1991

Effect of BHT 920 on calcium-activated K+ channels in renal epithelioid MDCK cells.

In Madin Darby canine kidney (MDCK) cells, epinephrine has been shown to increase intracellular calcium, activate calcium-dependent K+ channels and hyperpolarize the cell membrane. The present study has been performed to test for the possible involvement of alpha 2-adrenergic receptors. To this end, the effects of alpha 2-adrenoceptor agonist BHT 920 have been studied on cell membrane potential, ion channel activity and intracellular calcium: Similar to epinephrine, BHT 920 hyperpolarizes the cell membrane, increases intracellular calcium and activates inwardly rectifying K+ channels (single channel slope conductances 30-80 pS). Half-maximal hyperpolarization is achieved at concentrations between 10 and 100 nmol/l. The hyperpolarizing effect of BHT 920 is abolished in the presence of alpha 2-adrenoceptor antagonist yohimbine (100 nmol/l) but not in the presence of alpha 1-adrenoceptor antagonist prazosin (100 nmol/l). At extracellular calcium activity below 100 nmol/l BHT 920 still leads to a transient hyperpolarization of the cell membrane but, in contrast to epinephrine, is unable to significantly increase intracellular calcium or significantly activate the calcium-sensitive K+ channels. The observations indicate that stimulation of alpha 2-receptors participates in the epinephrine-induced increase of intracellular calcium, channel activation and hyperpolarization.

Adrenergic beta-Agonists↗
PubMed1991

Cellular mechanisms of bradykinin-induced hyperpolarization in renal epitheloid MDCK-cells.

Previous studies have demonstrated that bradykinin hyperpolarizes the cell membrane of subconfluent MDCK cells by increase of the potassium conductance. The present study has been performed to elucidate the intracellular mechanisms involved. To this end, the effects of bradykinin on the potential difference across the cell membrane (PD), on formation of inositol phosphates, and on intracellular calcium concentration (Cai) have been analyzed in cells without or with pretreatment with pertussis toxin or 12-O-tetradecanoylphorbol 13-acetate diester (TPA). In untreated cells, bradykinin leads to a transient increase of inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate, increase of Cai, activation of potassium channels and hyperpolarization of the cell membrane. The effects of bradykinin on PD and Cai are still present in the absence of extracellular calcium. In cells pretreated with pertussis toxin the effect of bradykinin on inositol trisphosphate formation is almost abolished but bradykinin still leads to a transient increase of Cai and PD in the presence and absence of extracellular calcium. In cells pretreated with TPA the bradykinin-induced increase of inositol trisphosphate formation is blunted, the bradykinin-induced increase of Cai abolished, but the bradykinin-induced hyperpolarization still present. The observations indicate that bradykinin increases Cai in part by phorbol ester and pertussis toxin sensitive activation of phospholipase C. In addition, bradykinin is capable of enhancing Cai by utilizing pertussis toxin insensitive mechanisms. Furthermore, bradykinin is able to transiently enhance the potassium conductance without a general increase of intracellular calcium.

Animals↗
PubMed1991

Bradykinin-induced oscillations of cell membrane potential in cells expressing the Ha-ras oncogene.

Products of ras genes are putative elements of growth factor signal transduction. However, the mechanism of action of these proteins in normal and malignant growth is as yet obscure. To test for functional consequences of ras oncogene expression, electrophysiological experiments were performed on NIH-3T3 fibroblasts transfected with a transforming Ha-ras MMTV-LTR construct expressing the oncogene on treatment with dexamethasone (+ras). Transfected cells in the absence of dexamethasone (-ras) and nontransfected cells in the presence of dexamethasone (oras) served as controls. In -ras and oras, bradykinin induces a single, transient hyperpolarization. In +ras, bradykinin elicits oscillations of cell membrane potential throughout the presence of the hormone by activation of calcium-sensitive K+ channels. The oscillations of cell membrane potential are abolished in the absence of extracellular calcium. As evident from fura 2 fluorescence, bradykinin leads to a transient increase of intracellular calcium both in the presence and absence of extracellular calcium. Oscillations of intracellular calcium could be observed in +ras cells, if bradykinin was applied at reduced extracellular sodium concentration possibly to impair calcium extrusion via the sodium/calcium exchange. Bradykinin induces oscillations of cell membrane potential similarly in -ras cells loaded with GTP[S], a nonhydrolyzable analogue of GTP. Thus, the altered response of ras oncogene expressing cells to bradykinin relates to the GTP binding property of the ras protein. It is concluded that in cells expressing ras oncogene but not in other fibroblasts bradykinin mimicks the effect of growth factors on the cell membrane.

Bradykinin↗
PubMed1991

Further analysis of ATP-mediated activation of K+ channels in renal epithelioid Madin Darby canine kidney (MDCK) cells.

ATP activates K+ channels by increasing intracellular calcium activity in Madin Darby canine kidney (MDCK) cells. The present study has been performed to test for the involvement of G-proteins and of protein kinase C in the intracellular transmission of these effects. To this end, the effect of ATP on intracellular calcium and K+ channel activity has been studied in cells pretreated with the phorbol ester 12-O-tetradecanoyl-phorbol 13-acetate (TPA) and/or pertussis toxin. The ATP-induced increase of intracellular calcium is not significantly affected by pretreatment with pertussis toxin, is significantly blunted by pretreatment with TPA and is abolished by pretreatment with both pertussis toxin and the phorbol ester. The ATP activation of K+ channels is similarly blunted by pretreatment with TPA, but is not abolished by pretreatment with both the phorbol ester and pertussis toxin. Furthermore, the ATP-induced hyperpolarization is not abolished in cells pretreated with both pertussis toxin and TPA. In those cells, ATP may activate K+ channels by calcium-dependent mechanisms or lead to localized increases of intracellular calcium sufficient to activate the K+ channels but escaping detection with fura-2 fluorescence.

Adenosine Triphosphate↗
PubMed1989

The effect of hypoosmolarity on the electrical properties of Madin Darby canine kidney cells.

The present study has been performed to test for the effect of hypotonic extracellular fluid on the electrical properties of Madin Darby canine kidney (MDCK)-cells. The volume of suspended MDCK-cells is 1,892 +/- 16 fl (n = 8) in isotonic (298.7 mosmol/l) extracellular fluid. Exposure of the cells to hypotonic (230.7 mosmol/l) extracellular fluid is followed by cellular swelling to 2,269 +/- 18 fl (n = 4) and subsequent volume regulatory decrease to 2,052 +/- 22 fl (n = 4) within 512 s. Volume regulatory decrease is abolished by quinidine (1 mmol/l) and by lipoxygenase inhibitor nordihydroguaiaretic acid (50 mumol/l). The potential difference across the cell membrane averages -53.6 +/- 0.9 mV (n = 49) in isotonic extracellular perfusates. Reduction of extracellular osmolarity depolarizes the cell membrane by +25.7 +/- 0.8 mV (n = 67), reduces the apparent potassium selectivity of the cell membrane, from 0.55 +/- 0.07 (n = 9) to 0.09 +/- 0.01 (n = 26), and increases the apparent chloride selectivity from close to zero to 0.34 +/- 0.02 (n = 21). Potassium channel blocker barium (1 mmol/l) depolarizes the cell membrane by +15.2 +/- 1.1 mV (n = 13). In the presence of barium, reduction of extracellular osmolarity leads to a further depolarization by +14.0 +/- 1.4 mV (n = 12). Addition of chloride channel blocker anthracene-9-COOH (1 mmol/l) leads to a hyperpolarization of the cell membrane by -6.7 +/- 2.2 mV (n = 11). In the presence of anthracene-9-COOH, reduction of the extracellular osmolarity leads to a depolarization by +22.4 +/- 1.7 mV (n = 11).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Activation of potassium channels in renal epithelioid cells (MDCK) by extracellular ATP.

Extracellular ATP has been shown to stimulate transepithelial chloride transport in confluent Madin-Darby canine kidney (MDCK) cell layers and to enhance potassium conductance in subconfluent MDCK cells. The present study has been performed to test for the effect of extracellular ATP on channel activity in patches from subconfluent MDCK cells. Within 8 s, addition of extracellular ATP (10 mumol/l) leads to a sustained, but fully reversible, appearance of potassium-selective channels in cell-attached patches [increase of open probability from 0.03 +/- 0.02 (n = 10) to 0.50 +/- 0.07 (n = 6)]. With the use of pipettes filled with 145 mmol/l KCl, inwardly rectifying property of the channels is disclosed with a single-channel conductance of 65.7 +/- 3.1 pS (n = 9) at zero potential difference between pipette and bath and with a reversal potential of 75.4 +/- 2.0 mV (n = 5; pipette negative vs. reference in the bath). The open probability of the channels is not significantly modified by altering pipette potential from -50 mV, pipette positive, to 50 mV, pipette negative. At extracellular calcium activities of less than 10 nmol/l, ATP leads to a transient activation of channels. In conclusion, extracellular ATP activates inwardly rectifying potassium channels in the cell membrane of subconfluent MDCK cells. A sustained activation of the channels requires the presence of extracellular calcium and is probably mediated by increases in intracellular calcium.

Adenosine Triphosphate↗
PubMed1988

Effects of serotonin on electrical properties of Madin-Darby canine kidney cells.

The present study has been performed to test for the influence of serotonin on the potential difference across the cell membrane (PD) of Madin-Darby canine kidney (MDCK)-cells. Under control conditions PD averages -48.6 +/- 0.6 mV (n = 98). Increasing extracellular potassium concentration from 5.4 to 10 and 20 mmol/l depolarizes the cell membrane by +6.3 +/- 0.6 mV (n = 6) and +14.1 +/- 1.0 mV (n = 12), respectively. The cell membrane is transiently hyperpolarized to -67.8 +/- 0.8 mV (n = 63) by 1 mumol/l serotonin. In the presence of serotonin, increasing extracellular potassium concentration from 5.4 to 20 mmol/l depolarizes the cell membrane by +26.4 +/- 1.0 mV (n = 11). 1 mmol/l barium depolarizes the cell membrane by +15.7 +/- 1.3 mV (n = 17) and abolishes the effect of step increases of extracellular potassium concentration from 5.4 to 10 mmol/l. In the presence of barium, serotonin leads to a transient hyperpolarization by -26.3 +/- 1.0 mV (n = 16). During this transient hyperpolarization, the cell membrane is sensitive to extracellular potassium concentration despite the continued presence of barium. 10 mumol/l methysergide hyperpolarize the cell membrane by -7.2 +/- 2.0 mV (n = 6). In the presence of 10 mumol/l methysergide, the effect of serotonin is virtually abolished (+0.4 +/- 0.9 mV, n = 6). 1 mumol/l ketanserin, a 5-HT2 receptor blocking agent, ICS 205-930, a 5-HT3 receptor blocking agent, and phentolamine, an unspecific alpha-receptor blocking agent, do not significantly modify the effect of serotonin. In the nominal absence of extracellular calcium, the effect of serotonin is markedly reduced.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Antagonists↗
PubMed1988

Inward rectifier K channels in renal epithelioid cells (MDCK) activated by serotonin.

The present study has been performed to test for the effect of intracellular calcium and of serotonin on the channel activity in patches from subconfluent MDCK-cells. In inside-out patches, inwardly rectifying potassium-selective channels are observed with open probabilities of 0.01 +/- 0.01, 0.24 +/- 0.03 and 0.39 +/- 0.07, at 100 nmol/liter, 1 mumol/liter or 10 mumol/liter calcium activity, respectively. The single-channel slope conductance is 34 +/- 2 pS, if the potential difference across the patch (Vp) is zero, and approaches 59 +/- 1 pS, if Vp is -50 mV, cell negative. In the cell-attached mode, little channel activity is observed prior to application of serotonin (open probability = 0.03 +/- 0.03). If 1 mumol/liter serotonin is added to the bath perfusate, the open probability increases rapidly to a peak value of 0.34 +/- 0.04 within 8 sec. In continued presence of the hormone, the open probability declines to approach 0.06 +/- 0.02 within 30 sec. At zero potential difference between pipette and reference in the bath (i.e., the potential difference across the patch is equal to the potential difference across the cell membrane), the single-channel conductance is 59 +/- 4 pS. In conclusion, inwardly rectifying potassium channels have been identified in the cell membrane of subconfluent MDCK-cells, which are activated to a similar extent by increase of intracellular calcium activity to 1 mumol/liter and by extracellular application of 1 mumol/liter serotonin.

Animals↗