Calcium puffs are generic InsP(3)-activated elementary calcium signals andare downregulated by prolonged hormonal stimulation to inhibit cellular calcium responses

Elementary Ca2+ signals, such as 'Ca2+ puffs', which arise from the activat ion of inositol 1,4,5-trisphosphate receptors, are building blocks for loca l and global Ca2+ signalling. We characterized Ca2+ puffs in six cell types that expressed differing ratios of the three inositol 1,4,5-trisphosphate receptor isoforms. The amplitudes, spatial spreads and kinetics of the even ts were similar in each of the cell types. The resemblance of Ca2+ puffs in these cell types suggests that they are a generic elementary Ca2+ signal a nd, furthermore, that the different inositol 1,4,5-trisphosphate isoforms a re functionally redundant at the level of subcellular Ca2+ signalling. Horm onal stimulation of SH-SY5Y neuroblastoma cells and HeLa cells for several hours downregulated inositol 1,4,5-trisphosphate expression and concomitant ly altered the properties of the Ca2+ puffs. The amplitude and duration of Ca2+ puffs were substantially reduced. In addition, the number of Ca2+ puff sites active during the onset of a Ca2+ wave declined. The consequence of the changes in Ca2+ puff properties was that cells displayed a lower propen sity to trigger regenerative Ca2+ waves. Therefore, Ca2+ puffs underlie ino sitol 1,4,5-trisphosphate signalling in diverse cell types and are focal po ints for regulation of cellular responses.