Аннотация
1. Cytosolic free calcium ion concentration (Ca$^2+$i) and whole-cell
L-type Ca$^2+$ channel currents were measured during excitation-contraction
(E-C) coupling in single voltage-clamped rat cardiac ventricular
cells. The measurements were used to compute the total cellular efflux
of calcium ions through sarcoplasmic reticulum (SR) Ca$^2+$ release
channels (FSR,rel) and the influx of Ca$^2+$ via L-type Ca$^2+$
channels (FICa). 2. FSR,rel was elicited by depolarizing voltage-clamp
pulses 200 ms in duration to membrane potentials from -30 to +80
mV. Over this range, peak FSR,rel had a bell-shaped dependence on
clamp pulse potential. In all cells, the 'gain' of the system, measured
as the ratio, FSR,rel(max)/FICa(max), declined from about 16, at
0 mV, to much lower values as clamp pulse voltage was made progressively
more positive. We named this phenomenon of change in gain as a function
of membrane potential, 'variable gain'. At clamp pulse potentials
in the range -30 to 0 mV, the gain differed from cell to cell, being
constant at about 16 in some cells, but decreasing from high values
(approximately 65) at -20 mV in others. 3. At clamp pulse potentials
at which Ca$^2+$ influx (FICa) was maintained, FSR,rel also had
a small maintained component. When macroscopic Ca$^2+$ influx
was brief (1-2 ms, during 'tails' of FICa), FSR,rel rose rapidly
to a peak after repolarization and then declined with a half-time
of about 9 ms (typically). 4. The rising phase of Ca$^2+$i
transients could be interrupted by stopping Ca$^2+$ influx rapidly
(by voltage clamp). We therefore termed this phenomenon 'interrupted
SR Ca$^2+$ release'.(ABSTRACT TRUNCATED AT 250 WORDS)
- 8014907
- aniline
- animals,
- calcium
- calcium,
- channel
- channels,
- compounds,
- confocal,
- contraction,
- dyes,
- electrophysiology,
- fluorescent
- gating,
- gov't,
- heart,
- in
- ion
- membrane
- microscopy,
- myocardial
- myocardium,
- non-p.h.s.,
- non-u.s.
- p.h.s.,
- patch-clamp
- potentials,
- rats,
- research
- reticulum,
- ryanodine,
- sarcopla,
- sarcoplasmic
- smic
- support,
- techniques,
- u.s.
- vitro,
- wistar,
- xanthenes,
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