Relationship of Ca2+ sparks to STOCs studied with 2D and 3D imaging in feline oesophageal smooth muscle cells

1. We recorded Ca2+ sparks and spontaneous transient outward currents (STOC s) simultaneously in smooth muscle cells using whole-cell patch recording a nd a unique, highspeed widefield digital imaging system to monitor fluo-3 f luorescence in both two and three dimensions (2D and 3D). 2. In 2D imaging, the correlation between the amplitude of a spark and its corresponding STOC was a weak one, and 27% of the sparks failed to cause ST OCs. The STOCless sparks were not significantly different in amplitude from those that caused STOCs. 3. Three-dimensional imaging disclosed that STOCless sparks were located cl ose to the cell surface, and on average their apparent distance from the ce ll surface was not significantly different from the sparks that cause STOCs . 4. Statistical evaluation of spark clusters disclosed that there were regio ns of the cell where the probability of spark occurrence was high and other s where it was quite lower.