A calcium- and voltage-dependent chloride current in developing chick skeletal muscle

Area of Science:

• Cellular Electrophysiology
• Muscle Development

Background:

• Depolarization of embryonic chick myotubes triggers a rapid spike and a subsequent long-duration after-potential.
• The ionic mechanisms underlying this after-potential are critical for understanding muscle cell function and development.

Purpose of the Study:

• To elucidate the ionic basis of the long-duration after-potential in embryonic chick myotubes.
• To investigate the role of calcium and chloride currents in generating this electrical event.

Main Methods:

• Intracellular recordings from cultured myotubes.
• Whole-cell patch-clamp recordings from myoblasts and myoballs.
• Manipulations of extracellular ion gradients and intracellular ion injections.

Main Results:

• The after-potential's peak varied with the chloride gradient, indicating chloride conductance involvement.
• Calcium influx was essential, as its absence or replacement with cobalt abolished the after-potential.
• Strontium supported after-potentials, and intracellular calcium/strontium restored the ability to evoke them.
• Voltage-clamp studies revealed a calcium- and voltage-activated chloride current with specific activation and deactivation kinetics.

Conclusions:

• The long-duration after-potential is mediated by a calcium- and voltage-activated chloride current.
• This after-potential depolarizes myotubes for several seconds, potentially influencing myoblast fusion and spontaneous contractions.