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Biomedical subjects

A Herrmann-Frank

Publications and source records attributed to A Herrmann-Frank.

At least 19 recordsLinked to original sources
PubMed2004

[Malignant lymphoma competence network].

The competence network Malignant Lymphomas is one out of 3 oncological networks which have been funded by the German Federal Ministry of Education and Research since 1999. The network's activities are based on the work of the German lymphoma research groups, which have led to significant progress in the diagnosis and therapy of malignant lymphoma over the last few years. Based on this infrastructure, the network aims to establish a professional quality management for the diagnostics and treatment of malignant lymphomas. Key aspects of activity include: 1st the establishment of an IT-based information and communication platform, 2nd IT-based networking of study groups and collaborating centres of pathology and radiotherapy, 3rd epidemiological and health care-economical research, 4th research on improved and new therapeutical approaches, 5th evidence-based medicine. Further information is presented in http://www.lymphome.de.

Biomedical Research↗
PubMed2000

A multicenter study of 4-chloro-m-cresol for diagnosing malignant hyperthermia susceptibility.

UNLABELLED: Standardization of the in vitro contracture test (IVCT) for malignant hyperthermia (MH) susceptibility has resulted in very rare false negative tests. However, false positive results stigmatizing the patient seem to be more frequent than false negative results and make supplementary tests desirable. This multicenter approach studied the usefulness of an IVCT with 4-chloro-m-cresol (4-CmC), a ryanodine receptor-specific agonist for a better definition of MH susceptibility. Diagnosis made by the standard IVCT was compared with the results of this 4-CmC test on muscle specimens of 202 individuals from 6 European MH centers. In the 4-CmC test, the results of the MH susceptible group differed significantly from both the MH normal and the MH equivocal group. 4-CmC revealed a qualitatively dose response-curve similar to caffeine. A correlation index of r = 0.79 for the concentration thresholds underlined the strong concordance of the caffeine and the 4-CmC effects. The optimal threshold concentration was determined to be 75 microM in the pooled data of all centers and is much lower than that of caffeine (2 mM), suggesting a more than 25-fold higher affinity of 4-CmC. The predictive value of 4-CmC is as high as that of caffeine and consequently higher than that of halothane. 4-CmC seems to be a suitable drug to refine diagnosis of MH susceptibility and could be used as an additional test substance. IMPLICATIONS: Although in vitro contracture testing for malignant hyperthermia diagnosis is well standardized, with a relatively high sensitivity and specificity, false test results cannot be excluded and may be associated with serious disabilities for the concerned individuals. In this multicenter study, 4-chloro-m-cresol was evaluated as a new test substance for the in vitro contracture testing. Its use improves the accuracy of in vitro diagnosis of malignant hyperthermia susceptibility.

Caffeine↗
PubMed1999

Sarcoplasmic reticulum vesicles embedded in agarose gel exhibit propagating calcium waves.

In different cell types, activation of signal transduction pathways leads to the generation of calcium oscillations and/or waves. Due to this important impact for cellular function, calcium waves are the subject of intensive investigations. To study interactions of cell organelles with no influence of the cell membrane, sarcoplasmic reticulum (SR) vesicles and well-coupled mitochondria were reconstituted. For the first time, we demonstrate the generation and propagation of calcium waves in a suspension of sarcoplasmic reticulum vesicles, embedded in an agarose gel. The propagation dynamics resemble those of calcium waves in living cells. Moreover, the addition of well-coupled mitochondria leads to more pronounced and significantly faster propagating waves, demonstrating the importance of the mitochondrial Ca(2+) transport. The experimental and simulation results indicate the resemblance of the in vitro system to an excitable medium.

Aniline Compounds↗
PubMed1997

Functional characterization of a distinct ryanodine receptor mutation in human malignant hyperthermia-susceptible muscle.

Malignant hyperthermia is an inherited autosomal disorder of skeletal muscle in which certain volatile anesthetics and depolarizing muscle relaxants trigger an abnormally high release of Ca2+ from the intracellular Ca2+ store, the sarcoplasmic reticulum. In about 50% of cases, malignant hyperthermia susceptibility is linked to the gene encoding the skeletal muscle ryanodine receptor/Ca2+ release channel (RYR1). To date, eight point mutations have been identified in human RYR1. Although these mutations are thought to lead to an increased caffeine and halothane sensitivity in the contractile response of skeletal muscle, their functional consequences have not been investigated on the molecular level. In the present study, we provide the first functional characterization of a point mutation located in the central part of RYR1, Gly2434 --> Arg. Using high affinity [3H]ryanodine binding as the experimental approach, we show that this mutation enhances the sensitivity of RYR1 to activating concentrations of Ca2+ and to the exogenous and diagnostically used ligands caffeine and 4-chloro-m-cresol. In parallel, the sensitivity to inhibiting concentrations of Ca2+ and calmodulin was reduced, transferring the mutant Ca2+ release channel into a hyperexcitable state.

Calcium↗
PubMed1996

Calmodulin sensitivity of the sarcoplasmic reticulum ryanodine receptor from normal and malignant-hyperthermia-susceptible muscle.

Ca2+ release from sarcoplasmic reticulum (SR) of malignant-hyperthermia-susceptible (MHS) muscle is hypersensitive to Ca2+ and caffeine. To determine if an abnormal calmodulin (CaM) regulation of the SR Ca(2+)-release-channel-ryanodine-receptor complex (RYR1) contributes to this hypersensitivity, we investigated the effect of CaM on high-affinity [3H]ryanodine binding to isolated SR vesicles from normal and MHS pig skeletal muscle. CaM modulated [3H]ryanodine binding in a Ca(2+)-dependent manner. In the presence of maximally activating Ca2+ concentrations, CaM inhibited [3H]ryanodine binding with no differences between normal and MHS vesicles. In the absence of Ca2+, however, CaM activated [3H]ryanodine binding with a 2-fold-higher potency in MHS vesicles. Significant differences between normal and MHS tissue were observed for CaM concentrations between 50 nM and 10 microM. A polyclonal antibody raised against the central region of RYR1 specifically inhibited this activating effect of CaM without affecting the inhibition by CaM. This indicates that the central region of RYR1 is a potential binding domain for CaM in the absence of Ca2+. It is suggested that in vivo an enhanced CaM sensitivity of RYR1 might contribute to the abnormal high release of Ca2+ from the SR of MHS muscle.

Animals↗
PubMed1996

4-Chloro-m-cresol: a specific tool to distinguish between malignant hyperthermia-susceptible and normal muscle.

Single-channel recordings have indicated that ryanodine receptor (RyR1) mutation Arg615Cys of porcine malignant hyperthermia-susceptible (MHS) muscle is not directly associated with the enhanced caffeine sensitivity of MH(S) muscle [1]. In the present study, the effect of a novel activator of RyR1, 4-chlorom-cresol (4-CmC), was investigated on high-affinity [3H]ryanodine binding to porcine skeletal sarcoplasmic reticulum. The 4-CmC affinity of [3H]ryanodine binding to MHS vesicles was 2-fold higher compared to that in normal tissue. This enhanced affinity was confirmed when the effect of 4-CmC on [3H]ryanodine binding to the isolated CHAPS-solubilized MHS RyR1 was investigated. 4-CmC is, therefore, suggested to be a potent tool to distinguish between Ca2+ release from MHS and normal muscle.

Animals↗
PubMed1996

4-Chloro-m-cresol, a potent and specific activator of the skeletal muscle ryanodine receptor.

The aim of the present study was to determine the effects of 4-chloro-m-cresol (4-CmC), a preservative often added to drugs intravenously administered, on the skeletal muscle sarcoplasmic reticulum (SR) Ca2+ release channel/ryanodine receptor. In heavy SR vesicles obtained from rabbit back muscles, 4-CmC stimulated (Ca2+)-activated [3H]ryanodine binding with an EC50 of about 100 microM. In the same concentration range, 4-CmC directly activated the isolated Ca2+ release channel reconstituted into planar lipid bilayers. The sensitivity to 4-CmC was found to be higher when applied to the luminal side of the channel suggesting binding site(s) different from those of nucleotides and caffeine. In skeletal muscle fibre bundles obtained from biopsies of patients susceptible to malignant hyperthermia, a skeletal muscle disease caused by point mutations in the ryanodine receptor, 4-CmC evoked caffeine-like contractures. Contrary to caffeine which induces contractures in millimolar concentrations, the threshold concentration for 4-CmC was 25 microM compared to 75 microM for non-mutated control fibres. Since these data strongly indicate that 4-CmC specifically activates SR Ca2+ release also in intact cell systems, this substance might become a powerful tool to investigate ryanodine receptor-mediated Ca2+ release in muscle and non-muscle tissue.

Animals↗
PubMed1996

Regulation of the purified Ca2+ release channel/ryanodine receptor complex of skeletal muscle sarcoplasmic reticulum by luminal calcium.

45Ca2+ flux and single channel measurements have related that the Ca2+ release channel/ryanodine receptor complex of striated muscle is regulated by micromolar cytoplasmic Ca2+. The effect of luminal Ca2+, however, remains controversial. In the experiments presented here, we reconstituted the isolated Ca2+ release channel of rabbit skeletal muscle sarcoplasmic reticulum into planar lipid bilayers in the presence of symmetrical K+ solutions. Using K+ as the charge carrier, we were able to examine the effect of changes in luminal calcium in the micro- to millimolar range. In the presence of activating cytoplasmic Ca2+, the release channel was activated and inactivated in a concentration-dependent manner by luminal Ca2+. Since increasing cytoplasmic EGTA concentrations shifted the dependence of channel open probability on luminal Ca2+ to higher Ca2+ concentrations, it is suggested that luminal Ca2+ exerts ist regulating effect by acting on Ca2+ binding sites accessible from the cytoplasmic side of the channel.

Animals↗
PubMed1996

Activation of the skeletal muscle ryanodine receptor by suramin and suramin analogs.

Ca2+ release from skeletal muscle sarcoplasmic reticulum is activated by adenine nucleotides and suramin. Because suramin is known to interact with ATP-binding enzymes and ATP receptors (P2-purinergic receptors), the stimulation by suramin has been postulated to occur via the adenine nucleotide-binding site of the ryanodine receptor/Ca2+-release channel. We tested this hypothesis using suramin and the following suramin analogs: NF037, NF018, NF023, and NF007. The suramin analogs stimulate the binding of [3H]ryanodine binding to sarcoplasmic reticulum membranes with the following rank order of potency: suramin (EC50 = approximately 60 microM) > NF037 (EC50 = approximately 150 microM) > NF018 > NF023 > NF007. The suramin-induced stimulation occurs via a myoplasmic binding site on the ryanodine receptor as confirmed by binding experiments and single-channel recordings with the purified protein. This binding site is different than that for ATP, a conclusion that is supported by the following observations: (i) Suramin stimulates the association rate and inhibits the dissociation rate of [3H]ryanodine, whereas ATP analogs increase only the on-rate. (ii) In the presence of suramin but not of ATP analogs, [3H]ryanodine binding is resistant to the inhibitory effect of millimolar Mg2+ and Ca2+. (iii) ATP analogs and suramin have an additive effect on [3H]ryanodine binding. (iv) Affinity labeling of the purified ryanodine receptor with 2',3'-dialdehyde [alpha-32P]ATP or after in situ oxidation of [gamma-32P]ATP is not affected by suramin. Thus, our results show that suramin acts as a direct and potent stimulator of the ryanodine receptor but that this action is mediated via a binding site different from that for adenine nucleotides.

Adenine Nucleotides↗
PubMed1995

Activation and labelling of the purified skeletal muscle ryanodine receptor by an oxidized ATP analogue.

We have tested the periodate-oxidized ATP analogue 2',3'-dialdehyde adenosine triphosphate (oATP) as a ligand for the skeletal muscle ryanodine receptor/Ca(2+)-release channel. Ca2+ efflux from passively loaded heavy sarcoplasmic reticulum vesicles of skeletal muscle is biphasic. oATP stimulates the initial phase of Ca2+ release in a concentration-dependent manner (EC50 160 microM), and the efflux proceeds with a half-time in the range 100-200 ms. This oATP-modulated initial rapid Ca2+ release was specifically inhibited by millimolar concentrations of Mg2+ and micromolar concentrations of Ruthenium Red, indicating that the effect of oATP was mediated via the ryanodine receptor. The purified Ca(2+)-release channel was incorporated into planar lipid bilayers, and single-channel recordings were carried out to verify a direct interaction of oATP with the ryanodine receptor. Addition of oATP to the cytoplasmic side activated the channel with an EC50 of 76 microM, which is roughly 30-fold higher than the apparent affinity of ATP. The oATP-induced increase in the open probability of the ryanodine receptor displays a steep concentration-response curve with a Hill coefficient of approximately 2, which suggests a co-operativity of the ATP binding sites in the tetrameric protein. oATP binds to the ryanodine receptor in a quasi-irreversible manner via Schiff base formation between the aldehyde groups of oATP and amino groups in the nucleotide binding pocket. This allows for the covalent specific incorporation of [alpha-32P]oATP by borhydride reduction. A typical adenine nucleotide binding site cannot be identified in the primary sequence of the ryanodine receptor. Our results demonstrate that oATP can be used to probe the structure and function of the nucleotide binding pocket of the ryanodine receptor and presumably of other ATP-regulated ion channels.

Adenosine Triphosphate↗
PubMed1993

Enhancement of Ca2+ release channel activity by phosphorylation of the skeletal muscle ryanodine receptor.

The Ca2+ release channel of rabbit skeletal muscle sarcoplasmic reticulum (SR) can be phosphorylated by membrane associated protein kinase(s) utilizing endogenously synthesized or exogenously added ATP. The channel protein has been enriched in non-phosphorylated and phosphorylated form from heavy SR following solubilization with CHAPS (3-[(3-cholamidopropyl)dimethylammonio-1-propane-sulfonate) and ultracentrifugation on a linear sucrose/CHAPS gradient. Reconstitution of the isolated channels into planar bilayers shows that phosphorylation enhances the open probability by increasing the sensitivity towards micromolar Ca2+ and ATP. The phosphorylation induced enhancement of the channel activity can be reversed by purified protein phosphatase 2A.

Adenosine Triphosphate↗
PubMed1991

Functional characterization of the Ca(2+)-gated Ca2+ release channel of vascular smooth muscle sarcoplasmic reticulum.

The Ca(2+)-gated Ca2+ release channel of aortic sarcoplasmic reticulum (SR) was partially purified and reconstituted into planar lipid bilayers. Canine and porcine aorta microsomal protein fractions were solubilized in the detergent 3-[(3-cholamidopropyl)dimethyl-ammonio]-1-propane sulphonate (CHAPS) in the presence and absence of 3[H]-ryanodine and centrifuged through linear sucrose gradients. A single 3[H]-ryanodine receptor peak with an apparent sedimentation coefficient of 30 s was obtained. Upon reconstitution into planar lipid bilayers, the unlabelled 30 s protein fraction induced the formation of a Ca(2+)- and monovalent-ion-conducting channel (110 pS in 100 mM Ca2+, 360 pS in 250 mM K+). The channel was activated by micromolar Ca2+, modulated by millimolar adenosine triphosphate, Mg2+ and the Ca(2+)-releasing drug caffeine, and inhibited by micromolar ruthenium red. Micro- to millimolar concentrations of the plant alkaloid ryanodine induced a permanently closed state of the channel. Our results suggest that smooth muscle SR contains a Ca(2+)-gated Ca2+ release pathway, with properties similar to those observed for the skeletal and cardiac ryanodine receptor/Ca2+ release channel complexes.

Animals↗
PubMed1989

Isolation of a Ca2(+)-releasing factor from caffeine-treated skeletal muscle fibres and its effect on Ca2+ release from sarcoplasmic reticulum.

In the presence of 2 mM caffeine, skeletal muscles of the frog exert small irregular oscillations of single sarcomeres. A factor, released from these oscillating muscles, was partially purified, and its activity was tested on skinned fibres and isolated vesicles of the sarcoplasmic reticulum (SR). Purification was achieved in three steps by gel filtration and reversed phase chromatography, and the active compound of the released material was shown probably to be a small peptide. In skinned fibres, the purified factor evoked repetitive contractions and subthreshold sarcomeric oscillations. In 'heavy' SR vesicles passively loaded with 45Ca2+, the factor induced a small but significant increase in the 45Ca2+ efflux rate. At the single channel level, the open probability of the SR Ca2+ release channel increased when the factor was added to the cytoplasmic side of the channel. The results reveal that the released factor potentiates Ca2+ release from the SR by increasing the open time of the Ca2+ release channel.

Amino Acids↗
PubMed1989

Caffeine- and Ca2(+)-induced mechanical oscillations in isolated skeletal muscle fibres of the frog.

Isometric force and subthreshold sarcomeric oscillations were studied in isolated muscle fibres of the frog. In intact muscle fibres, caffeine in a concentration of 2 mM caused a subthreshold oscillatory activation of single sarcomeres, called 'sarcomeric oscillations'. They occurred independently of membrane potential and were blocked by agents which directly interfere with Ca2+ release from the sarcoplasmic reticulum (SR). In skinned muscle fibres, sarcomeric oscillations were also induced by the Ca2+ ion itself (pCa = 6.1). When the free EGTA concentration of the bathing solutions was reduced, fibres responded with long lasting oscillations of force. Both types of oscillations were blocked when the membranes of the SR were solubilized by detergent. The results reveal that caffeine- and Ca2+-induced oscillations in skeletal muscle fibres are triggered by a cyclic release of Ca2+ ions from the SR. It is suggested that they interfere with the process of Ca2+-induced Ca2+ release.

Animals↗