| Excitable cells display dynamically regulated changes in the properties of ion currents during development. These changes are crucial for the proper maturation of cellular excitability, and therefore have the potential to affect more sophisticated functions, including neural circuits, movements, and behaviors. Zebrafish skeletal muscle is an excellent model for studying the development of ion channels and their contributions to excitability. They possess distinguishable populations of red and white muscle fibers, whose biological functions are well understood. The main objectives of this thesis were: (1) To characterize the development of muscle excitability by examining properties of voltage-gated sodium and potassium currents expressed in embryonic and larval zebrafish during the first week of development. (2) To elucidate some of the mechanisms by which ion current development might be controlled, beginning with activity-dependent and phosphorylation-dependent mechanisms.;The results revealed that properties of ion currents undergo a developmental progression, including increased current density, accelerated kinetics, and shifts in voltage-dependence; these developments correlated well with the maturation of muscle action potentials and the movements and behaviors they mediate. Sofa potato mutants were found to be deficient in certain aspects of ion current development, but other aspects appeared to be unaffected by a lack of synaptic activity. Protein kinase A demonstrated the ability to drastically reduce potassium current density; however the effects of PKA were similar at all developmental stages.;Overall, these findings provide novel insight into the roles played by voltage-gated currents during the development of excitability in zebrafish skeletal muscle, and expand the rapidly growing body of knowledge about ion channel function in general.;These objectives were approached using whole-cell electrophysiological techniques to examine the voltage-dependent and kinetic properties of voltage-gated sodium and potassium currents in intact zebrafish skeletal muscle preparations. Mutant sofa potato zebrafish, which lack functional nicotinic acetylcholine receptors, were then utilized to determine whether synaptic activity at the neuromuscular junction is required for proper ion current development. Finally, protein kinases were activated pharmacologically in order to determine whether they were able to modulate ion currents during development. |
