Abstract
Excitation-contraction coupling was studied in mammalian cardiac cells
in which the opening probability of L-type calcium (Ca$^2+$)
channels was reduced. Confocal microscopy during voltage-clamp depolarization
revealed distinct local transients in the concentration of intracellular
calcium ions (Ca$^2+$i). When voltage was varied, the latency
to occurrence and the relative probability of occurrence of local
Ca$^2+$i transients varied as predicted if Ca$^2+$ release
from the sarcoplasmic reticulum (SR) was linked tightly to Ca$^2+$
flux through L-type Ca$^2+$ channels but not to that through
the Na-Ca exchanger or to average Ca$^2+$i. Voltage had no
effect on the amplitude of local Ca$^2+$i transients. Thus,
the most efficacious "Ca$^2+$ signal" for activating Ca$^2+$
release from the SR may be a transient microdomain of high Ca$^2+$i
beneath an individual, open L-type Ca$^2+$ channel.
- 7754383
- animals,
- calcium
- calcium,
- channel
- channels,
- confocal,
- electric
- gating,
- gov't,
- guinea
- in
- ion
- membrane
- microscopy,
- myocardium,
- non-u.s.,
- p.h.s.,
- patch-clamp
- pigs,
- potentials,
- probability,
- research
- reticulum,
- sarcoplasmic
- stimulation,
- support,
- techniques,
- u.s.
- verapamil,
- vitro,
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