Stochastic modeling of spatially localized events in protein kinase A and Ca2+ signaling

Summary form only given. Many signaling events are essentially local with the signal traveling within submicromolar range. Thus information transferred in these pathways does not effect global changes, such as gene transcription, but rather local events close to the point of signal origin. Here I present the case of local signaling in the cross-talk between Ca and CAMP signaling pathway in the vicinity of L-type Ca²⁺ channel (LCC) and beta-adrenergic receptor (BAR). Recently it has been established that LCC and BAR can exist as multimolecular complexes comprising several members of signal transduction pathways, including BAR, LCC, a G protein, an adenylyl cyclase, PKA, AKAP and PP2A. Thus, the members of signaling pathways are mostly juxtaposed and immobile at the cell membrane. The only diffusing second messengers are Ca²⁺ and CAMP. Local signal transduction is in many instances essentially stochastic. For instance, it is estimated that 10 fYM concentration of Ca²⁺ in dyadic space in cardiac myocytes corresponds to approximately 10 ions. Simular estimates can be made for other diffusing compounds, including CAMP. These considerations led us to model BAR and LCC, separately and complex, using Monte Carlo Cell (MCell) simulation package allowing analysis of diffusion and interaction of single molecules within spatially limited compartments. We analyzed various aspects of signal transduction including facilitation of LCC and cross regulation of Ca²⁺ and CAMP production following stimulation of BAR and LCC. We studied the influence of the existence of positive and negative feedbacks in the extended signaling network and their effects on robustness of regulation. The model predictions were validated by experimental data obtained in collaboration with D. You´s and H. Colecraft´s laboratories at Johns Hopkins.