1. We sought to evaluate the contribution of the sarcoplasmic reticulum (SR) Ca2+ pump (vs. diffusion) to the kinetics of [Ca2+](i) decline during Ca2+ sparks, which are due to spontaneous local SR Ca2+ release, in isolated rat ventricular myocytes measured using fluo-3 and laser scanning confocal microscopy. Resting Ca2+ sparks were compared before (control) and after the SR Ca2+-ATPase was either completely blocked by 5 μM thapsigargin (TG) or stimulated by isoprenaline. Na+-Ca2+ exchange was blocked using Na+-free, Ca2+-free solution (0 Na+, 0 Ca2+) and conditions were arranged so that the SR Ca2+ content was the same under all conditions when Ca2+ sparks were measured. The control Ca2+ spark amplitude (281 ± 13 nM) was not changed by TG (270 ± 21 nM) or isoprenaline (302 ± 10 nM). However, the time constant of [Ca2+], decline was significantly slower in the presence of TG (29.3 ± 4.3 ms) compared with control (21.6 ± 1.5 ms) and faster with isoprenaline (14.5 ± 0.9 ms), but in all cases was much faster than the global [Ca2+](i) decline during a control twitch (177 ± 10 ms). 4. The spatial spread of Ca2+ during the Ca2+ spark was also influenced by the SR Ca2+ pump. The apparent 'space constant' of the Ca2+ sparks was longest when the SR Ca2+ pump was blocked, intermediate in control and shortest with isoprenaline. 5. We conclude that while Ca2+ diffusion from the source of Ca2+ release is the dominant process in local [Ca2+], decline during the Ca2+ spark, Ca2+ transport by the SR contributes significantly to both the kinetics and spatial distribution of [Ca2+](i) during the Ca2+ spark.
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal of Physiology|
|State||Published - Oct 15 1996|
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