Voltage-dependent Ca2+ channels are ubiquitous regulators of electrically excitable cells, initiating events as diverse as exocytosis, membrane excitability, cell motility, enzyme activation, and gene induction. Ca2+ influx through such channels is not simply a binary """"""""switch"""""""" that turns these responses on and off; rather, the rate, amplitude, and time course of intracellular Ca2+ signals strongly influence the degree and specificity of coupling between Ca2+ channels and downstream effector responses. Membrane voltage and G protein signaling pathways act together to fine-tune the gating of Ca2+ channels and, as a result, modulate the spatial and temporal properties of cytoplasmic Ca2+ signals. It is now well accepted that such coordinate regulation of Ca2+ channels in nerve terminals is an essential component of processing in the nervous system, providing a rapid and reversible means of altering synaptic strength. Surprisingly, no detailed studies have yet investigated the effects of Ca2+ channel modulation on other Ca2+ dependent cellular responses. Experiments in this application will rectify this deficit by evaluating the impact of G protein-dependent Ca2+ channel modulation on two somatic effector responses in dorsal root ganglion neurons--membrane excitability and gene transcription. Both responses are subject to activity-dependent regulation in sensory neurons, and both are strongly affected by somatic Ca2+ influx through voltage-gated channels. Given the dynamic control of Ca2+ channels that is provided by G protein signaling pathways in these cells, we hypothesize that G protein-dependent modulation will have significant impact on both acute and chronic responses to environmental stimuli. Experiments proposed here will define a set of molecular tools that alter G protein signaling and produce unique intracellular Ca2+ profiles in response to patterned, physiologically-appropriate stimuli. These stimuli (modeled after action potential waveforms and firing patterns characteristic of sensory neuron types in vivo) will then be employed to study short-term alterations in membrane excitability (mediated by Ca2+- activated Cl- channels) and long-term changes in gene transcription (mediated by the Ca2+-activated transcription factor, CREB). As sensory neuron plasticity underlies not only the normal adaptive responses of these cells to a changing environment but also their pathological responses to pain -- e.g., allodynia and hypersensitivity- identifying mechanisms that control Ca2+ influx in sensory neurons may allow development of new therapeutic strategies to treat chronic pain.
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