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L-type calcium current activation in cultured human myotubes
I Sipos1, C Harasztosi, W Melzer
1Department of Physiology, University Medical School of Debrecen, Hungary.
Journal of Muscle Research and Cell Motility
|June 1, 1997
Summary
Human skeletal muscle L-type calcium channels show slow activation kinetics. Nifedipine block can be reversed by UV light, revealing functional gating even when blocked.
Area of Science:
- Biophysics
- Molecular Biology
- Physiology
Background:
- L-type calcium channels are crucial for skeletal muscle excitation-contraction coupling.
- Understanding their activation kinetics is key to comprehending muscle function.
Purpose of the Study:
- To investigate the time course of skeletal muscle L-type calcium channel activation in human myotubes.
- To explore the functional gating properties of these channels in the presence of nifedipine.
Main Methods:
- Voltage-clamped human satellite cell-derived myotubes.
- Isolation of slow L-type calcium current using prepulses or nifedipine subtraction.
- UV-light flash photolysis to probe channel state.
Main Results:
- L-type current showed single exponential activation with minimal voltage dependence (+10 to +50mV).
- Nifedipine-block was partially reversible by UV light, revealing rapid and slow gating components.
- The fraction of channels rapidly restored by photolysis mirrored the L-type current time course, indicating functional slow gating.
Conclusions:
- Human skeletal muscle L-type calcium channels possess slow gating mechanisms that remain functional despite nifedipine block.
- Kinetic differences in L-type channel activation between human and frog muscle can be explained by minor alterations in gating parameters.