Voltage-gated calcium channels (VGCC) are of paramount importance for a wide range of physiological responses in excitable cells. VGCC are protein complexes consisting ofthe pore-forming 1 subunit and auxiliary subunits, such as the CaV subunit. CaV regulate the membrane expression and the gating properties of VGCC by associating to a region on the 1 subunit named AID ( interaction domain). Despite the highaffinity of the CaV/AID interaction, a number of studies suggested that the subunits may interactdynamically with the 1 subunit. In my thesis I investigated whether CaV subunits can dissociate and reassociate from VGCC, andthus modulate current properties by dynamic exchange of subunit isoforms in a native cell system. To test this hypothesis I developed a FRAP technique to study the dynamics of GFP-tagged 1 and subunits in triads of skeletal myotubes. Identical fluorescence recovery rates of 1S and 1a indicated stable channel complexes of these two skeletal muscle channel isoforms. However, all examined heterologous isoforms or 1a with an affinity-reducing mutation displayed higher FRAP rates,indicative of dynamic interactions with the channel complex.I next examined whether dynamic isoforms can be displaced from the channel by competing AID peptides in the host laboratory for the stay abroad (Dan Minor, UCSF). Analyisis of the current properties of calcium channels expressed in Xenopus oocytes revealed that of two dynamically associated isoforms only 3 but not 2a could be competed off the functional channel complex, upon AID peptide injections. The difference was reflected also in higher FRAP rates of 3 compared to 2a. Together these studies demonstrated a considerable heterogeneity of 1/ interactions and provide the basis for developing channel-specific modulators.