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.
- 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,
- smic
- support,
- techniques,
- u.s.
- vitro,
- wistar,
- xanthenes,
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