Voltage dependence of the pattern and frequency of discrete Ca2+ release events after brief repriming in frog skeletal muscle
AUTOR(ES)
Klein, Michael G.
FONTE
The National Academy of Sciences of the USA
RESUMO
Applying a brief repolarizing pre-pulse to a depolarized frog skeletal muscle fiber restores a small fraction of the transverse tubule membrane voltage sensors from the inactivated state. During a subsequent depolarizing test pulse we detected brief, highly localized elevations of myoplasmic Ca2+ concentration (Ca2+ “sparks”) initiated by restored voltage sensors in individual triads at all test pulse voltages. The latency histogram of these events gives the gating pattern of the sarcoplasmic reticulum (SR) calcium release channels controlled by the restored voltage sensors. Both event frequency and clustering of events near the start of the test pulse increase with test pulse depolarization. The macroscopic SR calcium release waveform, obtained from the spark latency histogram and the estimated open time of the channel or channels underlying a spark, exhibits an early peak and rapid marked decline during large depolarizations. For smaller depolarizations, the release waveform exhibits a smaller peak and a slower decline. However, the mean use time and mean amplitude of the individual sparks are quite similar at all test depolarizations and at all times during a given depolarization, indicating that the channel open times and conductances underlying sparks are essentially independent of voltage. Thus, the voltage dependence of SR Ca2+ release is due to changes in the frequency and pattern of occurrence of individual, voltage-independent, discrete release events.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=23600Documentos Relacionados
- Repriming and activation alter the frequency of stereotyped discrete Ca2+ release events in frog skeletal muscle.
- Activation of Ca2+ release by caffeine and voltage in frog skeletal muscle.
- Small event Ca2+ release: a probable precursor of Ca2+ sparks in frog skeletal muscle.
- Voltage dependence of inositol 1,4,5-trisphosphate-induced Ca2+ release in peeled skeletal muscle fibers.
- Decline of myoplasmic Ca2+, recovery of calcium release and sarcoplasmic Ca2+ pump properties in frog skeletal muscle.