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Single calcium channel behavior in native skeletal muscle

R T Dirksen¹, K G Beam

¹Department of Physiology, Colorado State University, Fort Collins 80523, USA.

The Journal of General Physiology

|February 1, 1995

Summary

Researchers identified two distinct calcium channels in skeletal muscle myotubes. The study reveals the 9-pS T-type calcium channel and the 14-pS L-type calcium channel, crucial for muscle function.

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Area of Science:

Physiology
Molecular Biology
Biophysics

Background:

Voltage-dependent calcium channels (VDCCs) play critical roles in cellular excitation-contraction coupling.
Skeletal muscle myotubes express various VDCCs, but their distinct unitary and macroscopic properties are not fully elucidated.
Understanding these properties is essential for comprehending calcium influx and downstream signaling pathways.

Purpose of the Study:

To investigate and compare the macroscopic and unitary behavior of voltage-dependent calcium channels in cultured skeletal muscle myotubes.
To identify the specific single-channel properties corresponding to T-type and L-type calcium currents.
To characterize the voltage-dependence and kinetics of these channels under controlled conditions.

Main Methods:

Utilized whole-cell and cell-attached patch-clamp electrophysiology on cultured skeletal muscle myotubes.
Employed BaCl2 as the charge carrier (110 mM) to record calcium channel activity.
Administered DHP agonist (Bay K 8644) and antagonist ((+)-PN 200-110) to differentiate channel types.

Main Results:

Identified two distinct calcium channel populations: a DHP-insensitive 9-pS channel (T current) and a DHP-sensitive 14-pS channel (L current).
The 9-pS channel exhibited rapid activation/inactivation with a threshold near -40 mV.
The 14-pS channel, enhanced by Bay K 8644, showed slow activation (approx. 20 ms), minimal inactivation, and a threshold near -10 mV; (+)-PN 200-110 increased null sweeps for this channel.

Conclusions:

The 9-pS and 14-pS channels are the respective single-channel correlates of T-type and L-type calcium currents in native skeletal muscle.
This study provides the first direct comparison of T- and L-type calcium channel properties under identical experimental conditions.
The findings contribute to a deeper understanding of calcium channel diversity and function in skeletal muscle.

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