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Relationship between L‐type Ca 2+ current and unitary sarcoplasmic reticulum Ca 2+ release events in rat ventricular myocytes
Author(s) -
Collier Mei Lin,
Thomas Andrew P.,
Berlin Joshua R.
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.1469-7793.1999.117aa.x
Subject(s) - depolarization , time constant , nifedipine , membrane potential , chemistry , analytical chemistry (journal) , calcium , endoplasmic reticulum , biophysics , electrical engineering , biochemistry , biology , organic chemistry , chromatography , engineering
1 The time courses of Ca 2+ current and Ca 2+ 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 Cd 2+ ‐sensitive Ca 2+ currents. In most cells, individual Ca 2+ sparks were observed by reducing Ca 2+ current density with nifedipine (0.1‐8 μM). 2 Ca 2+ sparks elicited by depolarizing voltage‐clamp pulses had a peak [Ca 2+ ] 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. 3 The time between the beginning of a depolarization and the initiation of each Ca 2+ 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 Ca 2+ current. This analysis showed that the time constants describing Ca 2+ current and Ca 2+ 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 Ca 2+ spark occurrence was significantly larger than the time constant of the Ca 2+ current. 4 A simple model is developed using Poisson statistics to relate macroscopic Ca 2+ current to the opening of single L‐type Ca 2+ channels at the dyad junction and to the time course of Ca 2+ spark occurrence. The model suggests that the time courses of macroscopic Ca 2+ current and Ca 2+ spark occurrence should be closely related when opening of a single L‐type Ca 2+ channel initiates a Ca 2+ spark. By comparison with the data, the model suggests that Ca 2+ sparks are initiated by the opening of a single L‐type Ca 2+ channel at all membrane potentials encountered during an action potential.