Calcium transients associated with the T type calcium current in myotubes

Area of Science:

• Muscle Physiology
• Cellular Electrophysiology
• Calcium Signaling

Background:

• Immature skeletal muscle cells express high T-type calcium current density and low L-type channels.
• The role of T-type calcium current in calcium transients is largely unexamined.
• Voltage sensors are crucial for excitation-contraction coupling, but T-type current's role is unclear.

Purpose of the Study:

• To investigate the role of T-type calcium current in generating calcium transients in cultured skeletal muscle myotubes.
• To compare the contribution of T-type current to calcium transients in normal and dysgenic myotubes.
• To understand the relationship between T-type calcium influx and intracellular calcium changes.

Main Methods:

• Whole-cell patch clamp technique on cultured myotubes (normal and dysgenic mice).
• Calcium indicator dye Fluo-3 used to measure intracellular calcium.
• Pharmacological manipulation (amiloride) and electrophysiological protocols (prepulses, depolarization steps) applied.

Main Results:

• T-type calcium current activated by weak depolarizations, peaking around -20 mV.
• In normal myotubes, calcium transients followed T-type current at low potentials but not high potentials.
• In dysgenic myotubes, calcium transients consistently followed T-type current integral and amplitude across potentials.
• Blocking T-type current reduced calcium transients in both normal and dysgenic myotubes.

Conclusions:

• T-type calcium current plays a significant role in calcium transients in immature skeletal muscle cells.
• The contribution of T-type current to calcium transients is evident, particularly when L-type channels are absent or at specific membrane potentials.
• These findings provide insights into the complex mechanisms of calcium handling during skeletal muscle development and function.