Zusammenfassung
Recent developments have led to great progress toward determining
the mechanism by which calcium is released from the sarcoplasmic
reticulum in the heart. The data support the notion of calcium-induced
calcium release via a calcium-sensitive release channel. Calcium
release channels have been isolated and cloned. This situation creates
a paradox, as it has also been found that calcium release is smoothly
graded and closely responsive to sarcolemmal membrane potential,
properties that would not be expected of calcium-induced calcium
release, which has intrinsic positive feedback. There is, therefore,
no quantitative understanding of how the properties of the calcium
release channel can lead to the macroscopic physiology of the whole
cell. This problem could, in principle, be solved by various schemes
involving heterogeneity at the ultrastructural level. The simplest
of these require only that the sarcolemmal calcium channel be located
in close proximity to one or more sarcoplasmic reticulum release
channels. Theoretical modeling shows that such arrangements can,
in fact, resolve the positive feedback paradox. An agenda is proposed
for future studies required in order to reach a specific, quantitative
understanding of the functioning of calcium-induced calcium release.
- 1325933
- animal
- animals,
- calcium
- calcium,
- cell
- cells,
- channels,
- comparative
- contraction,
- cultured,
- cytosol,
- dietary
- digestion,
- feed,
- female,
- fish
- gov't,
- growth
- heart,
- hormone,
- human
- hypoxia,
- indoles,
- lactation,
- mitochondria,
- myocardial
- myocardium,
- non-u.s.
- p.h.s.,
- products,
- proteins,
- rats,
- research
- reticulum,
- rumen,
- sarcoplasmic
- soybeans,
- study,
- support,
- u.s.
Nutzer