Key result
In feline oesophageal smooth muscle cells, 27% of Ca2+ sparks failed to cause spontaneous transient outward currents (STOCs) despite similar amplitudes and distances from the cell surface.
3D imaging reveals that a significant proportion of Ca2+ sparks in feline oesophageal smooth muscle cells do not trigger STOCs despite being located near the cell surface.
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Questions uniform Ca2+ spark-STOC coupling in smooth muscle; hypothesis-generating for physiology and requires human validation before clinical relevance.
We recorded Ca2+ sparks and spontaneous transient outward currents (STOCs) simultaneously in smooth muscle cells using whole-cell patch recording and a unique, high-speed widefield digital imaging system to monitor fluo-3 fluorescence in both two and three dimensions (2D and 3D). 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 STOCs. The STOCless sparks were not significantly different in amplitude from those that caused STOCs. Three-dimensional imaging disclosed that STOCless sparks were located close to the cell surface, and on average their apparent distance from the cell surface was not significantly different from the sparks that cause STOCs. Statistical evaluation of spark clusters disclosed that there were regions of the cell where the probability of spark occurrence was high and others where it was quite low.
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Kirber et al. (2001) studied this question. 2D and 3D imaging of Ca2+ sparks and STOCs was evaluated on Correlation between the amplitude of a spark and its corresponding STOC. In feline oesophageal smooth muscle cells, 27% of Ca2+ sparks failed to cause spontaneous transient outward currents (STOCs) despite similar amplitudes and distances from the cell surface.
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