LOCALIZED CALCIUM SPIKES AND PROPAGATING CALCIUM WAVES

Ca2+ signals control or modulate diverse cellular processes such as ce ll growth, muscle contraction, hormone secretion, and neuronal plastic ity [1-3]. Elevations in intracellular Ca2+ concentrations can be high ly localized to micron and submicron domains [4, 5] or propagated as i ntra- and intercellular waves over distances as large as 1 mm [6-8]. L ocalized, subcellular Ca2+ spikes are thought to selectively activate effector systems such as Ca2+ activated chloride currents in pancreati c acinar cells [9], neurotransmitter release in synaptic nerve termina ls [4, 10, 11], and morphological changes in neural growth cones [5, 1 2, 13]. In contrast, long-ranged Ca2+ waves synchronize the activities of different cytoplasmic regions of a single cell, such as cortical g ranule exocytosis after egg fertilization [6, 7] or coordinate the act ivities of many cells, such as ciliary beating in pulmonary epithelium [8, 14, 15]. The purpose of this review is to delineate the role of C a2+ in the generation of localized, subcellular Ca2+ spikes and long-r anged intracellular and intercellular Ca2+ waves.