Patterns of elevated free calcium and calmodulin activation in living cells.

The temporal and spatial dynamics of intracellular signals and protein effectors are being defined as a result of imaging using fluorescent reagents within living cells. We have described a new class of fluorescent analogues termed optical biosensors, which sense chemical or molecular events through their effects on protein transducers. One example of this new class of indicators is MeroCaM, an environmentally sensitive fluorophore which when it is attached to calmodulin reflects the activation of calmodulin by calcium in vitro. We report here that the rise in free calcium and MeroCaM activation occur in the same period during serum stimulation of quiescent fibroblasts. MeroCaM activation also correlates with the spatial pattern of increased free calcium and the contraction of transverse fibres during wound healing. Finally, migrating fibroblasts in the later stages of wound-healing exhibit an increasing gradient of free calcium and MeroCaM activation from the front to the rear.