This talk is based on work of Ian Parker (Univ. of California, Irvine).
The application of confocal imaging techniques has resolved a hierarchy of subcellular release events that underlie calcium spikes and waves. The best known paradigm for such a hierarchical organization of calcium release events evoked by inositol trisphosphate (IP3) is illustrated by progressive recruitment of calcium `blips' and `puffs' in Xenopus oocytes. Recent data show that these form a continuum of events involving liberation of varying amounts of calcium; probably as a result of stochastic recruitment of variable numbers of channels within functional clusters. Optical techniques thus provide a means to monitor activity of single calcium channels within intact cells, and to study their interactions to produce coordinated global signals.