Removal of extracellular Na+ for 520 ms was associated with a fourfold increase in Ca2+ spark frequency in rat ventricular myocytes, suggesting Na+-Ca2+ exchange locally regulates resting Ca2+.
Effect estimate: fourfold increase
To determine whether Na+-Ca2+ exchange modulates Ca2+ sparks, we studied enzymatically isolated patch clamped rat ventricular myocytes loaded with the Ca2+-sensitive indicator fluo-3, using confocal microscopy at 20-22 C. Two-dimensional images of Ca2+ sparks were recorded at 240 Hz using a laser scanning confocal microscope, allowing observation of a large area of the cell (820 microm2) 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+-Ca2+ exchange bidirectionally, was associated with a fourfold increase in spark frequency, without a significant change in cytoplasmic Ca2+, sarcoplasmic reticulum (SR) Ca2+ content, or spark intensity, size or time course. 3. These findings are consistent with a model of excitation-contraction coupling in which Na+-Ca2+ exchange locally regulates the resting Ca2+ concentration in the diadic cleft (T-tubule-SR junction), thereby modulating the threshold for triggering Ca2+ sparks.
Goldhaber et al. (Fri,) reported a other. Removal of extracellular Na+ vs. Baseline (holding potential of -75 mV) was evaluated on Ca2+ spark frequency (fourfold increase). Removal of extracellular Na+ for 520 ms was associated with a fourfold increase in Ca2+ spark frequency in rat ventricular myocytes, suggesting Na+-Ca2+ exchange locally regulates resting Ca2+.