Fig. 4. Ca²⁺ puffs in 16HBE14o- and SH-SY5Y cells. (A) High-frequency non-regenerative Ca²⁺ puffs in a 16HBE14o- cell. The top two traces depict Ca²⁺ puffs firing at the sites marked by the correspondingly coloured circles in the inset cell image. The ticks beneath the second trace denote the occurrence of a Ca²⁺ puff at either of the sites. The average frequency of events in this recording was 0.8 Hz. Despite this high frequency, there was only a modest effect on the global Ca²⁺ concentration (bottom trace). (B) The relatively slow elevation of the intracellular Ca²⁺ concentration observed in some SH-SY5Y cells. Although the cell shown had two active pacemaker Ca²⁺ puff sites, a regenerative Ca²⁺ rise was not observed. Instead, there was a steady shallow Ca²⁺ increase. The dashed lines in the cell images represent the positions of the nuclei.