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M Knipper

Publications and source records attributed to M Knipper.

32 records · Page 2Linked to original sources
PubMed1993

Neurotrophin induced cAMP and IP3 responses in PC12 cells. Different pathways.

NGF and BDNF elevate cAMP and IP3 levels in membranes of PC12 cells within a subsecond time period. The cAMP formation induced by NGF and BDNF pretreatment for 2 s was reduced by GDP-beta-S and PTX, but not the trkNGFR inhibitor K 252a. NGF, but not BDNF, induced IP3 formation. IP3 formation was reduced by K 252a, but not by GDP-beta-S and PTX. Using p75NGFR expressing, but trkNGFR-deficient PCNA cell membranes, NGF and BDNF induced cAMP formation, but not IP3 formation. We suggest that NGF and BDNF induced cAMP formation is mediated via a p75NGFR/G-protein mediated mechanism, and IP3 formation via a K 252a sensitive pathway.

Animals↗
PubMed1993

Neurotrophin induced second messenger responses in rat brain synaptosomes.

Neurotrophins (NGF, BDNF) elicit significant elevation of cAMP as well as IP3-concentrations in either membrane preparations or intact isolated nerve endings from rat brain hippocampus. The induced second messenger responses in membrane preparations were detectable in the subsecond time range. The IP3-level reached a maximum after a few hundred ms; whereas the cAMP-level continued to rise even after several seconds. The IP3-response but not the cAMP-signal was inhibited in the presence of the tyrosine kinase blocker K252a, suggesting that the two second messenger cascades were triggered via different mechanisms. The results suggest that neurotrophins may induce short-term effects in nerve terminals via second messenger pathways.

Animals↗
PubMed1992

Regulation of hemicholinium binding sites in isolated nerve terminals.

High-affinity uptake of choline, the rate-limiting, regulatory step for the synthesis of acetylcholine is regulated via presynaptic auto- and heteroreceptors. Binding studies using tritiated hemicholinium-3 ([3H]HCh-3) as the specific ligand for the choline carrier revealed that the number of hemicholinium binding sites in nerve terminals isolated from insect brain changes corresponding to the activity of synaptosomal kinase A and kinase C. Activation of kinase A apparently increases the total number of hemicholinium binding sites by recruiting additional occult carriers, whereas the effect of kinase C activity is most appropriately explained by preventing a down-regulation of carrier proteins. The kinase-mediated regulation of choline transporters is obviously due to a phosphorylation of the carrier protein itself.

Animals↗
PubMed1991

Purification and reconstitution of the high affinity choline transporter.

The high-affinity choline transporter has been solubilized from synaptosomal membranes by various detergents. The solubilized carrier protein has been incorporated into liposomes after removal of the detergent by dialysis. Using the reconstitution of choline transport activity as an assay, the components catalyzing choline translocation were purified from the detergent extract by ion-exchange chromatography on a Mono-Q column followed by immunoaffinity chromatography. Monitoring the active fractions by sodium dodecylsulfate polyacrylamide gel electrophoresis and isoelectrofocussing gave one major protein with an apparent molecular weight of about 90,000 and an isoelectric point of pH 4.7. The isolated protein appeared to be heavily glycosylated as shown by lectin binding; upon treatment with endoglycosidase F the polypeptide was degraded to an apparent molecular weight of about 65,000. Accumulation of choline into liposomes reconstituted with the purified protein was driven by artificially imposed sodium gradients and inhibited by hemicholinium-3.

Animals↗
PubMed1990

Regulation of high affinity choline uptake.

High affinity uptake of choline, the rate-limiting, regulatory step for the synthesis of acetylcholine (ACh), was found to be regulated via presynaptic auto- and heteroreceptors. The transport rate was reduced by a muscarinic agonist and neuropeptides, but was significantly enhanced by octopamine. Intracellular messengers, including cyclic nucleotides, appear to modulate the transport activity, apparently by activating specific protein kinases.

Acetylcholine↗
PubMed1989

Isolation and reconstitution of the high-affinity choline carrier.

Monoclonal antibodies, which block the high-affinity uptake of choline in synaptosomal ghosts, have been used to purify a membrane polypeptide (80 kDa) from insect synaptosomal membranes. This isolated protein was found to catalyse the sodium-dependent, hemicholinium-sensitive accumulation of choline after reconstitution into liposomes, thus, apparently represents the high-affinity choline transporter.

Animals↗
PubMed1989

Muscarinic receptors modulating acetylcholine release from insect synaptosomes.

1. Cholinergic synapses in the central nervous system of insects contain inhibitory muscarinic receptors whose stimulation by agonists leads to a diminished output of acetylcholine; antagonists, like atropine, facilitate acetylcholine release. 2. The receptors involved appear to be of the M2-subtype. Upon activation of presynaptic receptors a significant reduction of the intrasynaptosomal cyclic AMP level as well as a significantly increased membrane potential was observed. 3. The observed membrane hyperpolarization is apparently not a consequence of a lower cyclic AMP level, thus both effects may offer alternative or synergistical mechanisms for modulating transmitter release.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1986

Regulation of the high affinity choline transport in locust synaptosomes by adenosine triphosphate.

The effect of various nucleotides on the high affinity choline accumulation by synaptosomes from locusts has been studied. Extracellular adenosine triphosphate (ATP) was found to inhibit the transport of choline, whereas the accumulation of gamma-aminobutyric acid was not affected. The ATP-effect could not be mimicked by other purine derivatives, and seems not be mediated by purinergic receptors, but rather hydrolysis of the phosphate appears to be essential.

Adenosine Triphosphate↗
PubMed1986

Black widow spider venom-induced release of neurotransmitters: mammalian synaptosomes are stimulated by a unique venom component (alpha-latrotoxin), insect synaptosomes by multiple components.

Synaptosomes isolated from the rat brain corpus striatum and locust head and thoracic ganglia were loaded with radioactive neurotransmitter ([3H]dopamine and [3H]acetylcholine, respectively) and then treated with alpha-latrotoxin and other fractions (fractions C, D and E of Frontali et al.8) obtained by Sephadex G200 column chromatography from black widow spider venom gland homogenates. As shown by sodium dodecyl sulphate-polyacrylamide gel electrophoresis, alpha-latrotoxin is a high Mr protein, whereas fractions C-E are mixtures of several proteins, that include small amounts of contaminating alpha-latrotoxin (especially in fraction C). In rat synaptosomes alpha-latrotoxin induced massive neurotransmitter release, and some release was induced also by high concentrations of fractions C and D. These responses were blocked almost completely by a monospecific anti-alpha-latrotoxin serum, indicating that they were all due to alpha-latrotoxin. Release of [3H]acetylcholine from locust synaptosomes was induced by the various preparations investigated. alpha-Latrotoxin was about 10-fold less potent in locust than in rat synaptosomes. The effects of fractions C-E tended to disappear with storage. The most active batches of fractions C and E were even more potent than alpha-latrotoxin, while the D fraction was approximately 5-fold less potent. The anti-alpha-latrotoxin antiserum inhibited part of the responses elicited by fractions C and E, but left fraction D almost unaffected. Release by D and E fractions was maintained even when Ca2+ was removed from the incubation medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1985

Choline fluxes in synaptosomal membrane vesicles.

Synaptic plasma membrane vesicles isolated from the highly cholinergic nervous tissue of insects were used to study the translocation of choline across the membrane via a high-affinity carrier-mediated mechanism energized by ion gradients as the sole driving force. The uphill movement of choline, energized mainly by the Na+ gradient, attained levels of choline severalfold the final equilibrium value at the peak of the overshoot. Efflux of choline required the presence of internal sodium ions and was promoted by external choline if Na+ was present. External choline inhibited choline efflux in the absence of sodium. It is concluded that the efflux of choline is in many aspects symmetrical with its uptake.

Animals↗
PubMed1981

[In vivo analysis of bone calcium by localized neutron activation of the hand in osteoporosis].

The calcium concentration of the bones of the hand measured by neutron activity was lowered in 93% of osteoporotic women aged between 50 and 60 years and in 66% of women between 60 and 70 years, whereas from the 8th decade onwards, only 5% had a bone calcium concentration of the hand less than that of controls. In the male sex, nearly 80% of osteoporotic patients, had a calcium concentration of the hand less than that of controls whatever their age. Considering the radiological criterion retained for the diagnosis of osteoporosis, the existence of at least one fracture of a vertebral body, the authors discuss the significance of these facts.

Adult↗
PubMed1978

New developments in renal physiopathology acquired using a quantitative renal functional test: the 197Hg uptake test.

The renal function of 331 obstructive uropathies, of which 112 were unilateral, were studied using the radioactive Hg renal uptake technique. The results obtained lead to the following observations: (1) Kidneys silent because of a chronic pelviureteric obstruction maintain a minimum function representing approximately one quarter of the normal value, which does not seem to be improved following the removal of the obstruction. (2) Operative relief of obstruction in unilateral obstructive uropathy, except for cases of silent kidneys, is followed by a significative improvement in the function of the kidney on the operated side in more than a third of the cases studied. (3) In 43% of obstructive uropathies considered as unilateral, the functional value of the two kidneys is decreased.

Adolescent↗
PubMedDate not supplied

A novel microperfusion system for the long-term local supply of drugs to the inner ear: implantation and function in the rat model.

Local therapy is practiced for middle and inner ear diseases but is usually restricted to cases of ear drum perforation or repeated invasive intratympanic drug application. Perfusion of drugs on the round window or through the scalae of animals using a pump system suggests that the chronic local drug treatment might also be feasible in humans. However, drug delivery systems that are currently on the market involve repeated reimplantation if they are to be used for long-term drug supply. A bone-anchored, totally implantable micro-drug delivery system (MDS) for patient-controlled drug supply has been developed [Lehner et al., 1997]. In this study, we show the first successful long-term in vivo test of the MDS micro-pump in rats. The process of implantation and first functional tests will be described. The biomaterial used to manufacture the delivery system did not cause any inflammation reaction in any of the 9 animals successfully implanted. After activation of the micro-pump, the drug reservoir and port was found to be fluid-tight. Bolus applications of tetrodotoxin (TTX) to the round window induced a transient decrease of evoked brainstem responses. In 2 animals which carried the MDS for more than 8 months the proper functioning of the pumping device was examined in a 2-3 week interval over a 3 month period. The MDS can be autoclaved even after long-term implantation and can then be reused for subsequent implantations. Designed for life-long implantation in humans, the demonstration of an effective long-term drug supply to the inner ear using the MDS provides an encouraging first step towards future long-term drug treatment of the inner ear in humans.

Administration, Topical↗