Zusammenfassung
New information has recently been obtained along two essentially parallel
lines of research: investigations into the fundamental mechanisms
of Ca$^2+$-induced Ca$^2+$ release (CICR) in heart cells,
and analyses of the factors that control the development of unstable
rhythms such as repolarization alternans. These lines of research
are starting to converge such that we can begin to understand unstable
and potentially arrhythmogenic cardiac dynamics in terms of the underlying
mechanisms governing not only membrane depolarization and repolarization
but also the complex bidirectional interactions between electrical
and Ca$^2+$ signaling in heart cells. In this brief review, we
discuss the progress that has recently been made in understanding
the factors that control the beat-to-beat regulation of cardiac Ca$^2+$
release and attempt to place these results within a larger context.
In particular, we discuss factors that may contribute to unstable
Ca$^2+$ release and speculate about how instability in CICR may
contribute to the development of arrhythmias under pathological conditions.
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