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Local regulation of the threshold for calcium sparks in rat ventricular myocytes: role of sodium‐calcium exchange
Author(s) -
Goldhaber Joshua I.,
Lamp Scott T.,
Walter Donald O.,
Garfinkel Alan,
Fukumoto Gary H.,
Weiss James N.
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.00431.x
Subject(s) - biophysics , calcium , chemistry , extracellular , endoplasmic reticulum , confocal , myocyte , pipette , sodium calcium exchanger , cytoplasm , confocal microscopy , sodium , calcium signaling , contraction (grammar) , coupling (piping) , endocrinology , biochemistry , biology , microbiology and biotechnology , materials science , optics , physics , organic chemistry , metallurgy
1 To determine whether Na + ‐Ca 2+ exchange modulates Ca 2+ sparks, we studied enzymatically isolated patch clamped rat ventricular myocytes loaded with the Ca 2+ ‐sensitive indicator fluo‐3, using confocal microscopy at 20–22 °C. Two‐dimensional images of Ca 2+ sparks were recorded at 240 Hz using a laser scanning confocal microscope, allowing observation of a large area of the cell (820 μm 2 ) at one time. 2 At a holding potential of −75 mV, spontaneous sparks were infrequent. Removal of extracellular Na + for 520 ms, which in the absence of pipette Na + should block Na + ‐Ca 2+ exchange bidirectionally, was associated with a fourfold increase in spark frequency, without a significant change in cytoplasmic [Ca 2+ ], sarcoplasmic reticulum (SR) Ca 2+ content, or spark intensity, size or time course. 3 These findings are consistent with a model of excitation‐contraction coupling in which Na + ‐Ca 2+ exchange locally regulates the resting Ca 2+ concentration in the diadic cleft (T‐tubule‐SR junction), thereby modulating the threshold for triggering Ca 2+ sparks.