IMAGING THE HIERARCHICAL CA2-CELLS( SIGNALING SYSTEM IN HELA)

1. Confocal microscopy was used to investigate hormone-induced subcell ular Ca2+ release signals from the endoplasmic reticulum (ER) in a pro totype non-excitable cell line (HeLa cells). 2. Histamine application evoked two types of elementary Ca2+ signals: (i) Ca2+ blips arising fr om single ER Ca2+ release channels (amplitude, 30 nM; lateral spreadin g, 1.3 mu m); (ii) Ca2+ puffs resulting from the concerted activation of several Ca2+ blips (amplitude, 170 nM; spreading, 4 mu m). 3. Ca2waves in the HeLa cells arose from a variable number of initiation sit es, but for individual cells, the number and subcellular location of t he initiation sites were constant. The kinetics and amplitude of globa l Ca2+ signals were directly proportional to the number of initiation sites recruited. 4. Reduction of the feedback inherent in intracellula r Ca2+ release caused saltatoric Ca2+ waves, revealing the two princip al steps underlying wave propagation: diffusion and regeneration. Thre shold stimulation evoked abortive Ca2+ waves, caused by the limited re cruitment of Ca2+ puffs. 5. The hierarchy of Ca2+ signalling events, f rom fundamental levels (blips) to intermediate levels (puffs) to Ca2waves, is a prototype for Ca2+ signal transduction for non-excitable c ells, and is also analogous to the Ca2+ quarks, Ca2+ sparks and Ca2+ w aves in cardiac muscle cells.