Author's present address
Relationship between L-type Ca2+ current and unitary sarcoplasmic reticulum Ca2+ release events in rat ventricular myocytes
Article first published online: 8 SEP 2004
The Journal of Physiology
Volume 516, Issue 1, pages 117–128, April 1999
How to Cite
Collier, M. L., Thomas, A. P. and Berlin, J. R. (1999), Relationship between L-type Ca2+ current and unitary sarcoplasmic reticulum Ca2+ release events in rat ventricular myocytes. The Journal of Physiology, 516: 117–128. doi: 10.1111/j.1469-7793.1999.117aa.x
A. P. Thomas: Department of Pharmacology and Physiology, University of Medicine and Dentistry of New Jersey, 185 S. Orange Avenue, Newark, NJ 07103, USA.
- Issue published online: 8 SEP 2004
- Article first published online: 8 SEP 2004
- (Received 10 August 1998; accepted after revision 21 December 1998)
- 1The time courses of Ca2+ current and Ca2+ spark occurrence were determined in single rat ventricular myocytes voltage clamped with patch pipettes containing 0.1 μM fluo-3. Acquisition of line-scan images on a laser scanning confocal microscope was synchronized with measurement of Cd2+-sensitive Ca2+ currents. In most cells, individual Ca2+ sparks were observed by reducing Ca2+ current density with nifedipine (0.1-8 μM).
- 2Ca2+ sparks elicited by depolarizing voltage-clamp pulses had a peak [Ca2+] amplitude of 289 ± 3 nM with a decay half-time of 20.8 ± 0.2 ms and a full width at half-maximum of 1.40 ± 0.03 μm (mean ± s.e.m., n= 345), independent of the membrane potential.
- 3The time between the beginning of a depolarization and the initiation of each Ca2+ spark was calculated and data were pooled to construct waiting time histograms. Exponential functions were fitted to these histograms and to the decaying phase of the Ca2+ current. This analysis showed that the time constants describing Ca2+ current and Ca2+ spark occurrence at membrane potentials between -30 mV and +30 mV were not significantly different. At +50 mV, in the absence of nifedipine, the time constant describing Ca2+ spark occurrence was significantly larger than the time constant of the Ca2+ current.
- 4A simple model is developed using Poisson statistics to relate macroscopic Ca2+ current to the opening of single L-type Ca2+ channels at the dyad junction and to the time course of Ca2+ spark occurrence. The model suggests that the time courses of macroscopic Ca2+ current and Ca2+ spark occurrence should be closely related when opening of a single L-type Ca2+ channel initiates a Ca2+ spark. By comparison with the data, the model suggests that Ca2+ sparks are initiated by the opening of a single L-type Ca2+ channel at all membrane potentials encountered during an action potential.