Nerve cells convert electrical signals into changes in calcium ion to trigger biochemical responses. Only during stimulation or under pathological conditions are calcium levels elevated. Under normal conditions the intracellular calcium concentration is kept very low by a complex series of pathways that pump calcium out of the cell or into organelles. The objective of this proposal is to study three mechanisms by which calcium pumps embedded in the cell-surface membrane are modulated. 1) Kinases are signaling proteins that regulate many cell processes. The possibility that a kinase called Lyk modulates calcium pumps will be tested. Lyk modulation of calcium pumps would identify a novel point of cross-talk between the kinase and calcium signaling pathways in nerve cells. 2) In response to toxic stimuli, calcium pumps move from cell-surface to intracellular membranes. The mechanism of pump trafficking will be determined to provide insight into how neurons adapt to stress. 3) Nerve cells express multiple genetic variants of calcium pumps. The possibility that certain variants specialize in regulating the calcium that triggers neurotransmitter release, the basis for chemical communication between neurons, will be examined. To achieve these goals, neurons will be grown in culture (in a dish) and studied individually with optical and electrophysiological instrumentation.
Carrying out this project in a university setting creates an environment for training scientists. Undergraduate and predoctoral students, postdoctoral trainees and faculty on sabbatical leave have all contributed to and will continue to participate in this research.
Calcium acts as an intracellular messenger that triggers processes ranging from gene expression to the release of neurotransmitters and hormones. Thus, fluctuations in calcium trigger adaptive changes in neurons and play an essential role in cell-to-cell communication. This work will increase our understanding of how neurons process information at the molecular and cellular level.
PROJECT OUTCOMES Nerve cells convert electrical signals into changes in calcium ion to trigger biochemical responses. Only during stimulation or under pathological conditions are intracellular calcium levels elevated. Under normal conditions, the calcium concentration is kept very low by a complex series of pathways that pump calcium out of the cell or into organelles. The objective of this proposal was to study the mechanisms by which calcium pumps embedded in the cell-surface membrane are modulated. Neurons were grown in culture (in a dish) and studied individually with optical and electrophysiological instrumentation. We report findings on the modulation of the calcium pump and findings relating calcium changes to cell function. 1) We found that a protein on the cell surface modulated the calcium pump by activating a novel signaling cascade. This type of signaling could enable the cell to change calcium levels in response to its environment such as during cell-to-cell communication, cell movement and following injury. 2) Neurons respond to a variety of stimuli with a calcium increase. We found that the calcium pumps that remove the calcium from the cell interior respond differently depending on the source of calcium. This finding suggests that calcium pumps might be organized in to microdomains associated with particular calcium sources. This arrangement is important for understanding the modulation of cell function by drugs or hormones. 3) Calcium enters cells by specialized channels, some of which are aberrantly activated during disease. We found that expressing mutant proteins associated with certain disease states alter calcium entry and found that these disease proteins can be used to artificially increase calcium in order to understand physiological and pathological calcium signaling. 4) Information processing in the nervous system relies on changing the strength of connections between neurons called synapses. We found that calcium dependent changes in lipid-based signaling pathways altered synaptic plasticity. These findings provided insight into the effects of certain drugs on the nervous system and have implications for the development and repair of synaptic connections. Carrying out this project in a university setting creates an environment for training scientists. Undergraduate and predoctoral students, postdoctoral trainees and faculty on sabbatical leave have all contributed to this research. Fluctuations in calcium trigger adaptive changes in neurons and play an essential role in cell-to-cell communication. The results of these studies provide basic insight into how neurons regulate calcium levels to provide a foundation for understanding the effects of drugs and disease on the nervous system.
