Local regulation of the threshold for calcium sparks in rat ventricular myocytes: role of sodium-calcium exchange.
1. 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
J I
JI
The Cardiovascular Research Laboratories, Departments of Medicine (Cardiology), Physiology, and Physiological Sciences, UCLA School of Medicine, Los Angeles, CA 90095-1679, USA. jgoldhaber@mednet.ucla.edu
Lamp
S T
ST
Walter
D O
DO
Garfinkel
A
A
Fukumoto
G H
GH
Weiss
J N
JN
D000814:Aniline Compounds; D000818:Animals; D020746:Calcium Channels, L-Type / Q000378:metabolism; D002478:Cells, Cultured; D005456:Fluorescent Dyes; D006352:Heart Ventricles; D007091:Image Processing, Computer-Assisted; D018613:Microscopy, Confocal; D009206:Myocardium / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*; D014966:Xanthenes
D000814:Aniline Compounds; D020746:Calcium Channels, L-Type; D005456:Fluorescent Dyes; D019831:Sodium-Calcium Exchanger; D014966:Xanthenes; C059715:Fluo-3