CALCIUM SIGNALING IN RESTRICTED DIFFUSION SPACES

One- and two-dimensional models of Ca2+ diffusion and regulation were developed and used to study the magnitudes and the spatial and tempora l characteristics of the Ca2+ transients that are likely to develop in smooth muscle cells in restricted diffusion spaces between the plasma membrane and intracellular organelles. Simulations with the models sh owed that high [Ca2+] (on the order of several mu M) can develop in su ch spaces and persist for 100-200 ms. These Ca2+ transients could: 1) facilitate the coupling of Ca2+ influx to intracellular Ca2+ release; 2) provide a mechanism for the regulation of stored Ca2+ that does not affect the contractile state of smooth muscle; 3) locally activate sp ecific signal transduction pathways, before, or without activating oth er Ca2+ dependent pathways in the central cytoplasm of the cell. The l atter possibility suggests that independent enzymatic processes in cel ls could be differentially regulated by the same intracellular second messenger.