Regulation of L-type calcium channel inactivation

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Calcium ions enter neurons in the brain through calcium channels activated by a change in membrane voltage, a process that is critical to functions ranging from gene transcription to membrane excitability. Indeed, the importance of calcium as a signaling molecule dictates the need for systems to precisely regulate the timing and extent of calcium entry. The “L-type” (Cav1) class of calcium channels is widely expressed in the brain and is regulated by calmodulin (CaM), a molecule that modifies Cav1 calcium influx through a process of “calcium-dependent inactivation” (CDI) or “calcium-dependent facilitation” (CDF). Recent work reveals that Cav1-mediated calcium influx can be substantially increased by accessory proteins that bind to the channel C terminus to reduce CDI. Two examples are the scaffolding protein densin that binds to the C terminus to recruit the specialized kinase CaMKII, and a second is the calcium sensitive protein caldendrin that physically displaces CaM on the Cav1 channel. We have preliminary data for a novel form of Cav1.3 channel facilitation that lasts for >5 seconds (termed L-CDF) following a brief train of input characteristic of circuit activity. Moreover, Cav1.3 L-CDF depends on expression of densin and CaMKII. This is important, as each of these proteins are expressed in CA1 hippocampal pyramidal cells, where a “delayed facilitation” of calcium channel activity after a brief train of synaptic input enhances calcium influx. We hypothesize that the accessory proteins densin and caldendrin underlie the delayed facilitation that promotes a large increase in calcium influx in pyramidal cells. We will apply techniques ranging from molecular biology to biochemistry to electrophysiology to study L-type calcium channels expressed in a model system and in slices of rodent brain tissue to determine the role of densin and caldendrin in producing Cav1 channel L-CDF. Together this work represents the first step of attaining our long term goal of*understanding how L-type calcium channels are regulated to control*internal calcium and activation of second messenger pathways. The widespread expression of Cav1 channels in all tissues ranging from brain to muscle and heart will ensure that the results will be immediately important to understanding how calcium influx is controlled in multiple contexts, advancing knowledge of how the function of excitable cells in the body is regulated by these protein-protein interactions. **