The long term objectives of this study are to provide insights into the ways in which particular elements of the neuromuscular junction work. The strategy is to make quantitative structure-function correlations in situations where the difference in function can be specified, and where the corresponding structure is of special interest or relevance to synaptic transmission. The first group of comparisons will be among a series of three types of neuromuscular junctions which appear to differ in synaptic strength. The quantal content of the junctions will be estimated, and the probability of transmitter release at a single site for each type of junction will be compared with the intramembranous particle composition of its active zones as seen in freeze-fractured samples. A clear correlation between the number of particles observed at an active zone and the probability of release would support (but not prove) the hypothesis that some or all of these particles represent calcium channels. The methods include making intracellular and extracellular recordings from muscle fibers from the appropriate populations to obtain data for a quantal analysis. The same or comparable samples would then be fixed and prepared for freeze- fracture, thin-section, or scanning electron microscopic study of their ultrastructure. Each technique contributes to the structural data, which can be analyzed to obtain estimates of the average number of particles per active zone, the total number of active zones per junction, and the total number and length of junction per muscle fiber. Although the presence and role of calcium channels in synaptic transmission is well supported by physiological data, and the likelihood that they lie close to or within the morphological structure known as the active zone has been previously suggested, there is no direct evidence to describe their structure or precise location. Lacking an irreversible blocker for the calcium channel or similar "label" to precisely define their location, the experiments above represent the most reasonable approach to the question. Dr. Rheuben will participate in the Advanced Neurobiology Laboratory, which is a graduate level laboratory course in electrophysiology. She will also participate in the Neurobiology Journal Discussion series, which meets to discuss and critique recent papers of interest. In addition, she will organize an informal seminar series oriented toward graduate and under- graduate students. This project furthers VPW program objectives which are (1) to provide opportunities for women to advance their careers in engineering and in the disciplines of science supported by NSF and (2) to encourage women to pursue careers in science and engineering by providing greater visibility for women scientists and engineers employed in industry, government, and academic institutions. By encouraging the participation of women in science, it is a valuable investment in the Nation's future scientific vitality.
