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Biomedical subjects

M Müller

Publications and source records attributed to M Müller.

At least 505 records · Page 28Linked to original sources
PubMed1999

Quantitative detection of human complement factor H-related protein in transitional cell carcinoma of the urinary bladder.

OBJECTIVE: The purpose of this study was to assess a new quantitative urinary tumor marker for transitional cell carcinoma of the urinary bladder (TCC), human complement factor H-related protein (hCFHrp, BTA TRAK). METHODS: Urine samples of 298 individuals (76 healthy volunteers, 118 patients with benign urologic disorders, 104 patients with histologically proven bladder cancer) were examined for the presence of hCFHrp. Samples of all patients were obtained prior to therapy. RESULTS: In comparison to healthy volunteers, patients with TCC had significantly higher urinary levels of hCFHrp (117.60 vs. 2.05 U/ml; p < 0.001). HCFHrp levels were positively correlated with tumor grade and stage. Patients with invasive TCC had significantly higher levels of hCFHrp than patients with superficial TCC (p = 0.001). Marker levels in superficial bladder cancer at high risk of tumor progression (pT1G3) were significantly higher as compared to low and intermediate grade superficial cancers. Elevated levels of hCFHrp were also found in patients with benign urologic disorders (median: 72.65 vs. 117.60 U/ml in cancer patients). Using a cutoff of 17.1 U/ml, hCFHrp had a sensitivity of 72.1% and, due to a high rate of false-positive determinations in patients with benign urologic disorders, a total specificity of 50.5%. CONCLUSIONS: HCFHrp (BTA TRAK) is a sensitive test for detection of bladder cancer and for identification of patients at high risk. Due to a high rate of false-positive results in patients with benign urologic diseases, the test should not be used in an unselected population.

Adult↗
PubMed1999

Telomerase activity in malignant and benign renal tumors.

OBJECTIVES: An important characteristic of malignant cells is their unlimited replicative potential, their immortality. In conferring this immortality, the enzyme telomerase is believed to play a crucial role. The detection of telomerase activity provides new knowledge regarding the biologic growth behavior of tumors and offers new diagnostic and therapeutic tools. METHODS: In the present study the sensitive TRAP assay (telomeric repeat amplification protocol) was used to examine 44 malignant renal tumors and 8 benign tumors of the kidney and 52 specimens of normal renal tissue for telomerase activity. RESULTS: Telomerase activity was detected in 63% of tissue samples obtained from histologically confirmed renal cell carcinomas. In cases of renal cell carcinoma restricted to the kidney, telomerase activity was detected in 58%. In cases in which tumor growth has progressed beyond the limits of the organ, telomerase activity was found in 69%. This stage dependence, however, did not reach statistical significance. No correlation to tumor grading was observed. Telomerase activity was found less frequent in chromophobe renal cell carcinomas. Neither the 8 benign renal tumors (4 oncocytomas and 4 angiomyolipomas) nor the specimens of normal kidney showed any evidence of telomerase activity. CONCLUSIONS: The proportion of remarkable slow-growing renal cell carcinomas showing telomerase activity is less than in other malignancies and may correlate with biologic growth behavior. Possible explanations include the presence of an alternative pathway, called ALT (alternative lengthening of telomeres) and an association with the loss or presence of the telomerase suppressor on the short arm of chromosome 3. Prolonged follow-up will be of special interest to determine whether lack of telomerase activity predicts favorable outcome.

Adenoma, Oxyphilic↗
PubMed1999

Progesterone metabolism in the human kidney and inhibition of 11beta-hydroxysteroid dehydrogenase type 2 by progesterone and its metabolites.

Progesterone binds with high affinity to the mineralocorticoid (MC) receptor, but confers only very low agonistic MC activity. Therefore, progesterone is a potent MC antagonist in vitro. Although progesterone reaches up to 100 times higher plasma levels in late pregnancy than aldosterone, the in vivo MC antagonistic effect of progesterone seems to be relatively weak. One explanation for this phenomenon could be local metabolism of progesterone in the human kidney, similar to the inactivation of cortisol to cortisone by the 11beta-hydroxysteroid dehydrogenase (11beta-HSD) type 2. We studied the metabolism of progesterone in the human kidney in vitro and found reduction to 20alpha-dihydro (DH)-progesterone as the main metabolite. Ring-A reduction to 5alpha-DH-progesterone, 20alpha-DH-5alpha-DH-progesterone, and 3beta,5alpha-tetrahydro (TH)-progesterone was also documented. We further showed for the first time that 17-hydroxylation of progesterone (17alpha-OH-progesterone, 17alpha-OH, 20alpha-DH-progesterone), normally localized in the adrenals and the gonads, occurs in the human adult kidney. We found no formation of deoxycorticosterone from progesterone in the human adult kidney. Using human kidney cortex microsomes, we tested the inhibitory potency of progesterone and its metabolites on the 11beta-HSD type 2. The most potent inhibitor was progesterone itself (IC50 = 4.8 x 10(-8) mol/L), followed by 5alpha-DH-progesterone (IC50 = 2.4 x 10(-7) mol/L), 20alpha-DH-progesterone, 3beta,5alpha-TH-progesterone, 17alpha-OH-progesterone, and 20alpha-DH-5alpha-DH-progesterone (IC50 between 7.7 x 10(-7) mol/L and 1.3 x 10(-6) mol/L). The least potent inhibitor was 17alpha-OH,20alpha-DH-progesterone. In addition to progesterone metabolism by the kidney, the inhibition of 11beta-HSD type 2 by progesterone and its metabolites could be a second explanation for the weak MC-antagonist activity of progesterone in vivo. Inhibition of 11beta-HSD type 2 leads to an increase of intracellular cortisol in a way that the local equilibrium between the MC agonist cortisol and the antagonist progesterone is shifted to the agonist side.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1999

Glutathione S-conjugate transport in hepatocytes entering the cell cycle is preserved by a switch in expression from the apical MRP2 to the basolateral MRP1 transporting protein.

The multidrug resistance protein MRP1 and its isoform MRP2 are involved in ATP-dependent glutathione S-conjugate transport and have similar substrate specificities. MRP2 mediates hepatic organic anion transport into bile. The physiological function of MRP1 in hepatocytes is unknown. Previous results show that MRP1 expression is low in quiescent hepatocytes but increased after SV40 large T antigen immortalization, suggesting a relationship with cell proliferation. Therefore, we determined mrp1 and mrp2 expression in rat hepatocytes in relation to the cell cycle. By varying cell density we obtained cultures that are mainly in G1 (high density) or have progressed into the S-phase or beyond (low density). In both cultures mrp1 mRNA and protein levels are increased, concomitantly with the disappearance of mrp2. This switch from mrp2 to mrp1 occurs in the G1 phase of the cell cycle and is associated with a decreased cell polarity. Mrp1 is located on lateral membranes or on intracellular vesicles, depending on whether cell-cell contact is established. In both locations mrp1 contributes to cellular glutathione S-conjugate efflux and protects against oxidative stress-inducing quinones. We conclude that a switch in expression from the apically located mrp2 to the basolaterally located mrp1 preserves glutathione S-conjugate transport in hepatocytes entering the cell cycle and protects against certain cytotoxic agents.

ATP-Binding Cassette Transporters↗
PubMed1999

Induction of HPV16 capsid protein-specific human T cell responses by virus-like particles.

It has been postulated that upon binding to a cell surface receptor, papilloma virus-like particles (VLPs) gain entry into the cytosol of infected cells and the capsid proteins L1 and L2 can be processed in the MHC class I presentation pathway. Vaccination of mice with human papilloma virus-like particles consisting of capsid proteins L1 and L2 induced a CD8-mediated and perforin dependent protective immune response against a tumor challenge with human papilloma virus transformed tumor cells, which express only minute amounts of L1 protein. Here we show that HPV16 capsid proteins stimulate a MHC class I restricted CTL response with human peripheral blood lymphocytes (PBL) in vitro. The vigorous response was specific for VLP-infected target cells and was MHC class I restricted. Moreover we show the presence of at least one HLA-A*0201 restricted CTL epitope within the HPV-16 capsid proteins by using a VLP-'infected' HLA-A*0201 transfected human cell line as target cells. These results demonstrated that VLPs can induce a HPV16 capsid protein-specific immune response in humans, allowing the monitoring of immune responses induced by vaccines based on chimeric VLPs carrying additional immunogenic peptides or proteins in therapeutical applications in human patients.

Capsid↗
PubMed1999

Effects of serum starvation and re-cloning on the efficiency of nuclear transfer using bovine fetal fibroblasts.

The developmental potential of bovine fetal fibroblasts was evaluated using nuclear transfer. Fibroblasts from a 37-day-old fetus were fused to enucleated oocytes before activation. Nuclei of starved (cultured for 8 days in medium containing 0.5% serum) fibroblasts supported the development of reconstructed embryos to the blastocyst stage significantly better than those of non-starved fibroblasts (39% versus 20%; P < 0.05). When nuclear transfer morulae derived from starved or non-starved fibroblasts were used for re-cloning, the proportion of blastocysts (52 and 55%, respectively) obtained with these embryonic nuclei was significantly higher than it was with fibroblast nuclei used in the first round of nuclear transfer (P < 0.05 and P < 0.001, respectively). After transfer of blastocysts derived from non-starved and starved fibroblasts, respectively, 33% (1/3) and 78% (7/9) of recipients were pregnant on day 30 as assessed by ultrasonography. On day 90, the corresponding pregnancy rates were 33% (1/3) and 63% (5/8). Two live male twin calves, derived from non-starved fibroblasts, were delivered by Caesarean section at day 281 of gestation. This study demonstrates a positive effect of serum starvation on the efficiency of nuclear transfer using bovine fetal fibroblasts. The efficiency of nuclear transfer could be further increased by recloning.

Animals↗
PubMed1999

Safety and tolerability of naproxen ophthalmic solution in comparison to placebo.

BACKGROUND: Naproxen is a classic non-steroidal anti-inflammatory drug (NSAID) with established analgesic and anti-inflammatory potency. Its action is related to cyclooxygenase inhibition and consequent decrease in prostaglandin concentration in various fluids and tissues. Since prostaglandin release is involved in several ocular alterations, various NSAID eye drops have come into use in the clinical setting during the last decade. SUBJECTS, MATERIAL AND METHODS: A randomized, double-blind, placebo-controlled, three-way crossover design phase I was performed in 12 healthy volunteers to determine both tolerance and safety of a new NSAID ophthalmic solution containing sodium naproxen (0.1% and 0.2%). Both single dose and repeated dose (TID for 6 days) instillation were performed. Evaluation was entirely based upon tolerance criteria. Subjective and objective signs of ocular irritation and subject comfort preference were evaluated. Also medical examination, hematology, blood chemistry and urine analysis were also assessed to evaluate any possible effect of the test drugs and control. RESULTS: Neither ophthalmic tolerance parameters nor vital signs or laboratory parameters were influenced by treatments. A slight hyperemia of the conjunctiva was the only change observed in the eye during the study, whereas the only symptom mentioned was burning. CONCLUSION: It is concluded that both tolerability and safety of 0.1% and 0.2% naproxen solution are acceptable after single and repeated conjunctival administration.

Adult↗
PubMed1999

Detection of M. tuberculosis DNA in sarcoidosis: correlation with T-cell response.

The pathogenetic role of Mycobacterium tuberculosis (M. tuberculosis) in tuberculosis is well defined, whereas its role in sarcoidosis is controversial. In sarcoidosis, activation of T-helper cells is observed, which is comparable to tuberculosis. The aim of this study was first to investigate whether M. tuberculosis DNA could be retrospectively detected in samples of patients with clinically verified sarcoidosis by polymerase chain reaction (PCR) and second, to analyze the relationship between M. tuberculosis DNA positive samples and T-cell response in sarcoidosis patients. Formalin fixed paraffin-embedded lung tissues or cell sediments of bronchoalveolar lavage, respectively, from 65 patients with sarcoidosis and lung tissues from 40 tuberculosis patients were investigated by means of different PCR assays in comparison to control samples. The primers used were derived from insertion sequence IS 986/6110 specific for the M. tuberculosis complex (123 bp PCR) and from the gene encoding the 38 kDa protein antigen b (419 bp PCR). The 123 bp assay yielded a specificity of 97% and a sensitivity of 95%. In contrast, the 419 bp PCR method showed a lower sensitivity of only 8% likely because of possible DNA degradation during fixation and embedding procedures of the tissue and the fact that this PCR uses a single copy element as target. We amplified the M. tuberculosis complex specific 123 bp fragment in 64% of samples from sarcoidosis patients. The specificity of PCR products in these cases was confirmed by DNA sequencing. Interestingly in the M. tuberculosis positive sarcoidoses, we found increased serum levels of soluble interleukin-2 receptor in correlation to the sarcoidosis stages (p < 0.05). In conclusion, the determination of M. tuberculosis by PCR alone does not permit a differentiation between sarcoidosis and tuberculosis. However these results support the contention that M. tuberculosis may play a pathogenetic role at least in the part of sarcoidosis patients with elevated interleukin-2 receptor values.

Adult↗
PubMed1999

A retrospective study of dental conditions of captive brown bears (Ursus arctos spp.) compared with free-ranging Alaskan grizzlies (Ursus arctos horribilis).

The teeth of 63 skulls of brown bears (Ursus arctos spp.) that had lived in the Bernese bear pit between 1850 and 1995 were examined and radiographed for occlusion, loss of teeth, calcified dental plaque and calculus, attrition, and caries. Dental pathology and periodontal status were evaluated with respect to age and location in the dentition. Further techniques such as computed tomography, microhardness testing, histologic sectioning, and scanning electron microscopy were used in selected cases to verify the macroscopic and radiographic diagnoses. Fourteen skulls originating from free-ranging wild Alaskan brown bears (Ursus arctos horribilis) were examined as a control group. For zoo bears over 10 yr old, severe enamel and dentinal attrition has been observed in canine teeth, with exposed pulp and proximal lesions in molar teeth. Deposits of calcified dental calculus were found in various locations and increased with age. A much lower degree of calculus deposition was found in the Alaskan grizzlies, whose average caries frequency was higher but with large individual variation and different locations in canine teeth and occlusal lesions in molar and premolar teeth. Radiographic evaluation of perialveolar osteolytic processes revealed a greater frequency of apical and combined apical-marginal lesions of the alveoli in zoo bears over 10 yr old. Stereotypical behavior like cage chewing is a suspected cause of canine tooth and secondary alveolar lesions, whereas a nutritionally inappropriate diet and inadequate opportunities for tooth-cleaning activities are responsible for the lack of natural cleaning and the extensive calculus formation that results. The methods used in this study are useful in assessing and comparing the dental health status of free-ranging bears, and those living in zoological gardens, by evaluating anesthetized bears or bear skull collections representing both groups.

Age Factors↗
PubMed1999

Polyspecific organic anion transporting polypeptides mediate hepatic uptake of amphipathic type II organic cations.

Hepatic uptake of albumin-bound amphipathic organic cations has been suggested to be mediated by multispecific bile salt and organic anion transport systems. Therefore, we investigated whether the recently cloned rat organic anion transporting polypeptides 1 and 2 as well as the human organic anion transporting polypeptide might be involved in the hepatocellular uptake of bulky type II organic cations. In cRNA-injected Xenopus laevis oocytes, all three carriers mediated uptake of the known type II model compounds N-(4, 4-azo-n-pentyl)-21-deoxy-ajmalinium and rocuronium, whereas the newly synthesized type II model compounds N-methyl-quinine and N-methyl-quinidine were transported only by the human organic anion transporting polypeptide. This carrier-mediated uptake of N-methyl-quinine and N-methyl-quinidine was sodium-independent and saturable with apparent K(m) values of approximately 5 and approximately 26 microM, respectively. In contrast to bulky type II organic cations, more hydrophilic type I organic cations such as tributylmethylammonium and choline were not transported by any of the organic anion transporting polypeptides. These findings demonstrate that organic anion transporting polypeptides can also mediate hepatocellular uptake of type II organic cations, whereas uptake of small and more water-soluble type I cations is mediated by different transport systems such as the organic cation transporters.

Animals↗
PubMed1999

Resistance to CD95 (APO-1/Fas)-mediated apoptosis in human renal cell carcinomas: an important factor for evasion from negative growth control.

Disorders in negative growth control by CD95 (APO-1/Fas)-mediated apoptosis have been suggested to facilitate immune evasion of neoplastic cells and resistance to anticancer drugs. The present report describes the expression and function of CD95 receptor and ligand in human renal cell carcinomas (RCC) of all major histological types, presenting in vitro data on RCC cell lines (n = 30) and ex vivo observations in RCC tissue samples (n = 30). Using RT-PCR, flow cytometry and immunostaining, expression of CD95 receptor and ligand was found in human RCC of all major histological types. The expression levels of CD95 ligand, however, were rather low. Despite constitutive CD95 receptor expression, resistance to CD95-mediated apoptosis became evident from the weak response to agonistic anti-CD95 antibodies, which induced a low increase of apoptosis in only 9 of 30 RCC cell lines. After IFN-gamma pretreatment, however, apoptosis triggered by agonistic anti-CD95 antibodies was observed in 22 of 30 RCC cell lines. These data indicated that the machinery required for CD95-induced cell death was present, albeit inactive in most RCC. Inhibition of protein synthesis by cycloheximide resulted in increased sensitivity to agonistic anti-CD95 antibodies, suggesting a role for short-lived apoptosis-protective proteins in the resistance of RCC to CD95-mediated apoptosis. Moreover, we demonstrated the secretion of soluble CD95 receptor which might contribute to this resistance as well. In conclusion, resistance rather than responsiveness to CD95-mediated apoptosis is a key feature of human RCC. This resistance might facilitate evasion from negative growth control and contribute to the failure of cytotoxic drugs in the treatment of human RCC.

Apoptosis↗
PubMed1999

Formation of etheno adducts and their effects on DNA polymerases.

Etheno (epsilon) and related DNA adducts are formed from the reaction of certain bifunctional electrophiles with DNA. Our interest has been focused on oxiranes substituted with leaving groups, e.g. 2-chlorooxirane, the epoxide derived from the carcinogen vinyl chloride. The chemical mechanisms of the formation of the major etheno products derived from adenine, cytosine and guanine have been elucidated by nuclear magnetic resonance analysis and 13C-labelled precursors. The amounts of all major etheno adducts have been quantified in DNA treated with 2-chlorooxirane by coupled high-performance liquid chromatography of nucleoside and base products. 1,N2-epsilon-Gua, its formally hydrated but stable hemiaminal HO-ethanoGua (5,6,7,9-tetrahydro-7-hydroxy-9-oxoimidazo[1,2-a]purine) and 1,N2-ethanoGua have all been inserted at a single site in oligonucleotides. All three of these bases block polymerases, cause misincorporations and produce some mutations in bacteria. The patterns of blockage and substitution vary among polymerases. In nucleotide excision repair-deficient Escherichia coli, 1,N2-epsilon-Gua yielded a calculated 16% mutation frequency (base-pair substitutions) when the results were corrected for strand usage. 1,N2-epsilon-Gua was also examined in Chinese hamster ovary cells with a stable integration system; the mutants are more complex than observed in bacteria and include rearrangements, deletions and base-pair substitutions other than at the adduct site.

Animals↗
PubMed1999

[Immunological reactions and health complaints in biological refuse personnel and composting by biological aerosol exposure].

Employees in waste treatment industries are exposed to high levels of airborne microorganisms. Concentrations of 10(7) cfu/m3 air were measured in composting facilities, whereas exposures of bio-waste collectors were two orders of magnitude lower with exposure peaks up to 10(6) cfu/m3 air. These exposures were compared to specific antibody levels against molds and actinomycetes, work related health complaints, and diseases of the workers. 72 bio-waste collectors and 77 compost workers were examined and interviewed for work related symptoms, current occupational exposures, smoking habits, and exposures from other sources (farming, bird breeding, gardening) by physicians specialized in occupational medicine, using a standardized protocol. Levels of specific IgG antibodies to molds and actinomycetes occurring regularly at these workplaces were determined as biomarkers of exposure. The exposure data from the workplaces indicate a higher exposure of compost workers compared to bio-waste collectors. This corresponds with significantly increased health complaints of the upper airways and the skin and higher concentrations of specific antibodies against molds and actinomycetes in the compost workers. Atopic diseases were underrepresented in the compost workers compared to bio-waste collectors and population based data, indicating a healthy worker effect in this group. Occupational diseases from airborne microorganisms eligible for insurance compensation were observed in waste treatment facilities. More detailed studies are needed for exact assessment of health risks of workers in these industries.

Actinomycetales↗
PubMed1998

p53 activates the CD95 (APO-1/Fas) gene in response to DNA damage by anticancer drugs.

Chemotherapeutic drugs cause DNA damage and kill cancer cells mainly by apoptosis. p53 mediates apoptosis after DNA damage. To explore the pathway of p53-dependent cell death, we investigated if p53-dependent apoptosis after DNA damage is mediated by the CD95 (APO-1/Fas) receptor/ligand system. We investigated hepatoma, gastric cancer, colon cancer, and breast cancer cell lines upon treatment with different anticancer agents known to act via p53 accumulation. Cisplatin, mitomycin, methotrexate, mitoxantrone, doxorubicin, and bleomycin at concentrations present in the sera of patients during therapy led to an upregulation of both CD95 receptor and CD95 ligand. Induction of the CD95 ligand occurred in p53 wild-type (wt), p53 mutant (mt), and p53 deficient (p53(-/-)) cell lines and at wt and mt conformation of temperature-sensitive p53 mutants. In contrast, upregulation of the CD95 receptor was observed only in cells with wt p53, not in cells with mt or without any p53. Restitution of inducible wt p53 function restored the ability of p53(-/-) Hep3B cells to upregulate the CD95 receptor in response to anticancer drugs. This rendered the cells sensitive to CD95-mediated apoptosis. In an attempt to understand how CD95 expression is regulated by p53, we identified a p53-responsive element within the first intron of the CD95 gene, as well as three putative elements within the promoter. The intronic element conferred transcriptional activation by p53 and cooperated with p53-responsive elements in the promoter of the CD95 gene. wt p53 bound to and transactivated the CD95 gene, whereas mt p53 failed to induce apoptosis via activation of the CD95 gene. These observations provide a mechanistic explanation for the ability of p53 to contribute to tumor progression and to resistance of cancer cells to chemotherapy.

Antineoplastic Agents↗
PubMed1998

Cardiac specific expression of the green fluorescent protein during early murine embryonic development.

We demonstrate the establishment of transgenic mice, where the expression of the green fluorescent protein (GFP) is under control of the human cardiac alpha-actin promoter. These mice display cardiac specific GFP expression already during early embryonic development. Prominent GFP fluorescence was observed at the earliest stage of the murine heart anlage (E8). Cardiomyocytes of different developmental stages proved GFP positive, but the intensity varied between cells. We further show that contractions of single GFP positive cardiomyocytes can be monitored within the intact embryo. At later stages of embryonic development, the skeletal musculature was also GFP positive, in line with the known expression pattern of cardiac alpha-actin. The tissue specific labeling of organs is a powerful new tool for embryological as well as functional investigations in vivo.

Actins↗
PubMed1998

EblacZ tumor dormancy in bone marrow and lymph nodes: active control of proliferating tumor cells by CD8+ immune T cells.

A well-defined lacZ gene tagged DBA/2 lymphoma (EblacZ) was used to examine the role of host immune responses in controlling tumor dissemination and persistence, as well as metastasis. In s.c. and intra-ear pinna-inoculated mice, low numbers of EblacZ cells homed to the bone marrow and lymph nodes. The frequency of bone marrow-residing tumor cells did not change with the growth of primary tumor or with multiple inoculations of tumor cells. The bone marrow-residing tumor cells expressed the proliferation-associated Ki67 antigen and expanded upon CD8+ depletion. In contrast, inoculation of nu/nu or severe combined immunodeficiency mice or of immune-suppressed DBA/2 mice led to the rapid outgrowth of EblacZ cells in the bone marrow and their metastasis to other organs. Transfer of bone marrow from EblacZ immunized MHC congenic or syngeneic DBA/2 donors, but not from naive donors, protected s.c.-inoculated DBA/2 mice. Protection was abrogated by in vitro depletion of CD8+ T cells prior to transfer of bone marrow. These experiments show that bone marrow and lymph nodes are privileged sites where potentially lethal tumor cells are controlled in a dormant state by the immune system. Metastasis may be a consequence of the breakdown of this immune control.

Animals↗
PubMed1998

Inhibition of major cationic inward currents prevents spreading depression-like hypoxic depolarization in rat hippocampal tissue slices.

Hypoxia-induced spreading depression-like depolarization (hypoxic SD, or anoxic depolarization) is accompanied by the near-loss of membrane potential, severe reduction of membrane resistance, and influx of Na+, Ca2+, Cl- and water into neurons. The biophysical nature of these membrane changes is incompletely understood. In the present study we applied a pharmacological mixture (10 microM DNQX, 10 microM CPP, 1 microM TTX, and 2 mM Ni2+) to rat hippocampal tissue slices to inhibit major Na+ and Ca2+ inward currents. This inhibitory cocktail slightly depolarized CA1 pyramidal neurons and completely blocked all evoked potentials. In its presence severe hypoxia of up to 20 min duration failed to induce hypoxic SD and the accompanying intrinsic optical signal. Instead, only moderate, very slow negative shifts of the extracellular DC potential were observed. Following 10 min hypoxia and 1 hour wash-out of the inhibitors antidromic and orthodromic responses were still blocked but hypoxic SD with markedly delayed onset could be induced in most slices. In current-clamped CA1 pyramidal cells hypoxia induced a rapid, near-complete depolarization and decreased the input resistance by 89%. In the presence of the cocktail, however, hypoxia caused a gradual, partial depolarization, to about -40 mV; the membrane resistance decreased by only 37%. We conclude that simultaneous blockade of the known major Na+ and Ca2+ channels consistently prevents hypoxic SD. The hypothesis that SD initiation is the consequence of general loss of selective permeability or general membrane breakdown becomes unlikely. Instead, influx of Na+ and Ca2+ might play a crucial role in the generation of the rapid SD-like depolarization.

Animals↗