Membrane protein dynamics is of great importance for living organisms. The precise localization of proteins composing a synapse on the membrane facing a nerve terminus is essential for proper functioning of the nervous system. In muscle fibers, the nicotinic acetylcholine is densely packed under the motor nerve termini. A receptor associated protein, rapsyn, acts as a linker between the receptor and the other components of the synaptic suramolecular assembly. Advances in fluorescence microscopy have allowed to measure the behavior of a single receptor in the cell membrane. In this work single-molecule microscopy was used to track the motion of ionotropic acetylcholine (nAChR) and serotonin (5HT3R) receptors in the plasma membrane of cells. We present methods for measuring single-molecule diffusion and their analysis. Single molecule tracking has shown a high dependence of acetylcholine receptors diffusion on its associated protein rapsyn. Comparing muscle cells that either express rapsyn or are devoid of it, we found that rapsyn plays an important role on receptor immobilization. A three-fold increase of receptor mobility was observed in muscle cells devoid of rapsyn. However, in these cells, a certain fraction of immobilized receptors was also found immobile. Furthermore, nAChR were strongly confined in membrane domains of few tens of nanometers. This showed that membrane composition and membrane associated proteins influence on receptor localization. During muscle cell differentiation, the fraction of immobile nAChR diminished along with the decreasing nAChR and stable rapsyn expression levels. The importance of rapsyn in nAChR immobilization has been further confirmed by measurements in HEK 293 cells, where co-expression of rapsyn increased immobilization of the receptor. nAChR is a ligand-gated ion-channel of the Cys-loop family. In mammals, members of this receptor family share general structural and functional features. They are homo- or hetero-pentamers and form a membrane-spanning ion channel. Subunits have three major regions, an extracellular ligand binding domain, a transmembrane channel and a large intracellular loop. 5HT3R was used as a model to study the effect of this loop on receptor mobility. Single-molecule tracking experiments on receptors with progressively larger deletions in the intracellular loop did not show a dependence of the size of the loop on the diffusion coefficient of mobile receptors. However, two regions were identified to play a role in receptor mobility by changing the fractions of immobile and directed receptors. Interestingly, a prokaryotic homologue of cys-loop receptors, ELIC, devoid of a large cytoplasmic loop was found to be immobile or to show directed diffusion similar as the wild-type 5HT3R. The scaffolding protein rapsyn stabilizes nAChR clusters in a concentration dependent manner. We have measured the density and self-interactions of rapsyn using FRET microscopy. Point-mutations of rapsyn, known to provoke myopathies, destabilized rapsyn self-interactions. Rapsyn-N88K, and R91L were found at high concentration in the cytoplasm suggesting that this modification disturbs membrane association of rapsyn. A25V was found to accumulate in the endoplasmic reticulum. Fluorescent tools to measure intracellular concentration of calcium ions are of great value to study the function of neurons. Rapsyn is highly abundant at the neuromuscular junction and thus is a genuine synaptic marker. A fusion protein of rapsyn with a genetically encoded ratiometric calcium sensor has been made to probe synapse activity. This thesis has shown that the combined use of biologically relevant system and modern fluorescence microscopy techniques deliver important information on pLGIC behaviour in the cell membrane. / <p>QC 20151217</p>

Im Frühjahr/Sommer 2002 wurde eine Befragung von 51 erwachsenen Patienten im Raum Berlin-Brandenburg mit seltenen Muskelerkrankungen bzw. neuromuskulären Erkrankungen zu verschiedenen Aspekten der medizinischen Versorgung durchgeführt. Angewandte Methoden waren ein standardisierter Fragebogen sowie ein Leitfadeninterview. Vom ersten Arztbesuch bis zur in 59% der Fälle im Krankenhaus erfolgten Diagnosestellung einer Muskelerkrankung vergingen durchschnittlich 4,1 Jahre (Median: 1 Jahr). Es fanden sich eine unzureichende Anamneseerhebung und körperliche Untersuchung sowie eine mangelnde Überweisungsbereitschaft an Neurologen. Eine signifikante Verzögerung erlitten Patienten, die anstelle eines Hausarztes zunächst einen anderen Facharzt als den Neurologen aufgesucht hatten. 43% der Patienten hatten Schwierigkeiten, im Anschluss einen kompetenten Arzt für die Langzeitbetreuung zu finden. Fragen der Vererbbarkeit sowie der respiratorischen und kardialen Komplikationen wurden unzu! reichend besprochen. Im Verlauf erfolgte eine mangelnde Überwachung der respiratorischen sowie kardialen Funktion. Die Verordnung von Physiotherapie und Hilfsmitteln wurde dagegen gut bewertet. Bei 51% der Patienten kam es auch nach der Diagnosestellung zu Krankenhausaufenthalten. 22% der Patienten mussten wegen Komplikationen stationär behandelt werden. Insgesamt zeigten sich Defizite in der medizinischen Versorgung, wie sie z.T. bereits in Expertenstellungnahmen bzw. wenigen anderen Studien berichtet wurden. Für den Bereich der seltenen Erkrankungen gilt eine Spezialambulanz als geeignetes Versorgungsmodell, welches die spezialisierte, multidisziplinäre Betreuung der Patienten sichern soll. Solche Einrichtungen existieren mittlerweile in Deutschland, Outcome-Studien fehlen jedoch bisher. / In spring/summer 2002 a group of 51 adult patients in Berlin-Brandenburg suffering from a muscle or a neuromuscular disease were questioned concerning various aspects of their medical care. The applied methods were a standardized questionnaire and a qualitative interview. The average time between the first consultation of a physician and the establishment of the diagnosis of a muscle disease was 4,1 years (median: 1 year). 59% of the patients received their diagnosis at a hospital. An insufficient history-taking, lacks in the physical examination and a reluctance to refer the patient to a neurologist could be identified. There was a significant delay for those patients who initially consulted a non-neurological specialist instead of a general physician. 43% of the patients had difficulties in finding a qualified physician for the long-time care. The patients were insufficiently informed about the heredity of their disease and about possible respiratory and cardiac complicati! ons. There was a lack in following up the respiratory and cardiac functions of the patients. The prescription of physiotherapy and aids was rated positively by the patients. 51% of the patients had hospital stays also after having their diagnosis. 22% were admitted to hospital due to complications of their disease. In general, deficits in the medical care for these patients were shown, similar to those described in expert opinions or few preview studies. A specialized hospital-based outpatient centre that should ensure the specialized multidisciplinary care for the patients is regarded as the model for the medical care in the area of rare diseases. Similar centres exist in Germany by now, but there are no outcome-studies yet.