Abstract
1. Confocal microscopy and the fluorescent Ca$^2+$ indicator fluo-3
(K$^+$ salt) were used to measure cytosolic free calcium ion
concentration (Ca$^2+$) during excitation-contraction (E-C)
coupling in single, voltage-clamped, rat cardiac ventricular cells.
2. Local Ca$^2+$i transients were measured nearly simultaneously
in different, separate, subcellular volumes of approximately 2.0
microns 3. During depolarization, local Ca$^2+$i transients
were distinctly different from each other and from whole-cell Ca$^2+$i
transients. These differences were particularly apparent during small
depolarizations, and were substantially reduced by ryanodine. 3.
Components of the local Ca$^2+$i transients, particularly those
evoked by small depolarizations, were closely similar, in time course
and amplitude, to spontaneous local Ca$^2+$i transients, or
'sparks' (which have been shown previously to be Ca$^2+$ released
from sarcoplasmic reticulum). 4. Analysis of local Ca$^2+$i
transients in the spatial frequency domain (power spectrum) revealed
that high power at spatial frequencies of 0.05-0.2 microns-1 was
always associated with spontaneous calcium 'sparks' and with local
Ca$^2+$i transients evoked by small depolarizing pulses (e.g.
to -31 mV). Evoked local Ca$^2+$o transients in the presence
of ryanodine, and those evoked by depolarization to very positive
clamp-pulse potentials (+45 mV), were associated with considerably
lower power at this frequency. 5. The results suggest that whole-cell
Ca$^2+$i transients evoked by voltage-clamp depolarization,
and thus by L-type Ca$^2+$ current, are comprised of local Ca$^2+$i
transients that are similar to the spontaneous calcium 'sparks'.
At very positive clamp-pulse potentials, however, the electrically
evoked local Ca$^2+$i transients may be smaller, perhaps as
a result of smaller unitary L-type Ca$^2+$ current.
Description
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Tags
- 7853223
- Aniline
- Animals,
- Calcium
- Calcium,
- Channels,
- Compounds,
- Confocal,
- Dyes,
- Fluorescent
- Gov't,
- Heart,
- In
- Membrane
- Microscopy,
- Myocardium,
- Non-U.S.
- P.H.S.,
- Patch-Clamp
- Potentials,
- Rats,
- Research
- Reticulum,
- Ryanodine,
- Sarcopla,
- Support,
- Techniques,
- U.S.
- Vitro,
- Wistar,
- Xanthenes,
- smic