Functional Interactions in Ca²⁺ Signaling over Different Time and Distance Scales

Cytosolic Ca²⁺ plays a central role in the regulation of numerous aspects of cellular activity in virtually all cell types. Much of this versatility arises through the diverse mechanisms by which Ca²⁺ signals are generated and transmitted to act over very different time and distance scales. For example, Ca²⁺ can act in a very fast and highly localized manner, as in the triggering of neurotransmitter release within microseconds of Ca²⁺ entry through voltage-gated channels closely apposed to active release zones (Neher 1998); or it can evoke slower responses involving global Ca²⁺ elevations throughout the cell, as in the generation of Ca²⁺-dependent Cl⁻ currents by Ca²⁺ waves that take many seconds to sweep across Xenopus oocytes (Parker and Yao 1994). A common starting point in considering these...