Imaging the hierarchical Ca²⁺ signalling system in HeLa cells

Bootman, Martin; Niggli, Ernst; Berridge, Michael and Lipp, Peter (1997). Imaging the hierarchical Ca²⁺ signalling system in HeLa cells. The Journal of Physiology, 499(2) pp. 307–314.

Abstract

1. Confocal microscopy was used to investigate hormone-induced subcellular Ca²⁺ release signals from the endoplasmic reticulum (ER) in a prototype non-excitable cell line (HeLa cells).

2. Histamine application evoked two types of elementary Ca²⁺ signals: (i) Ca²⁺ blips arising from single ER Ca²⁺ release channels (amplitude, 30 nM; lateral spreading, 1.3 μm); (ii) Ca²⁺ puffs resulting from the concerted activation of several Ca²⁺ blips (amplitude, 170 nM; spreading, 4 μm).

3. Ca²⁺ waves in the HeLa cells arose from a variable number of initiation sites, but for individual cells, the number and subcellular location of the initiation sites were constant. The kinetics and amplitude of global Ca²⁺ signals were directly proportional to the number of initiation sites recruited.

4. Reduction of the feedback inherent in intracellular Ca²⁺ release caused saltatoric Ca²⁺ waves, revealing the two principal steps underlying wave propagation: diffusion and regeneration. Threshold stimulation evoked abortive Ca²⁺ waves, caused by the limited recruitment of Ca²⁺ puffs.

5. The hierarchy of Ca²⁺ signalling events, from fundamental levels (blips) to intermediate levels (puffs) to Ca²⁺ waves, is a prototype for Ca²⁺ signal transduction for non-excitable cells, and is also analogous to the Ca²⁺ quarks, Ca²⁺ sparks and Ca²⁺ waves in cardiac muscle cells.

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