The main hypothesis of this proposal is that different types of K+ and Ca2+ channels have specific functions and they are expressed depending on the biological status of the nerve muscle synapse. The main questions are: What types of K+ and Ca2+ channels are expressed at the mature motoneuron and its nerve terminal junction? Is the functional expression of the Ca2+ channel dependent upon protein kinase or phosphatase activity? What are the changes in K+ and Ca2+ channel expression or modulation during development? We plan to circumscribe our efforts and concentrate on the expression and localization of the L-type voltage dependent Ca2+ channel (L-VDCC), the Ca2+ activated K+ channel (Kv,ca), and the fast transient K+ channel (Kv4.2 and Kv4.3). To answer these questions we plan to study the following: 1. To determine the expression and modulation of L-VDCCs at the mature neuromuscular junction (NMJ). 2. To investigate the functional role of Kv4.2, Kv4.3 and Kv,ca at the mature motor nerve terminal. 3. To determine developmental associated changes in the functional role of K+ and Ca2+ channel subtypes at the neonatal NMJ. 4. To determine the expression levels and localization of different types of K+ and Ca2+ channel subunits in developing motoneuron soma and nerve terminals. We will measure spontaneous and evoked TR in the presence of K+ and Ca2+ channel specific blockers in nerve-muscle preparations to determine their participation in the release process. Extracellular presynaptic currents will be recorded via a perineural inserted microelectrode This will allow us to gain direct information about channels expressed in the nerve terminal related and unrelated to TR. Specific antibodies for the a subunits and their regulatory b subunits will be used to determine their expression. These studies will provide basic information on synaptic physiology which is a key point to understand NMJ disorders