Multiple classes of sulfhydryls modulate the skeletal muscle Ca2+ release channel

Area of Science:

• Biochemistry
• Molecular Biology
• Physiology

Background:

• The skeletal muscle Ca2+ release channel (ryanodine receptor) is crucial for excitation-contraction coupling.
• Sulfhydryl groups play a significant role in regulating channel function.
• Understanding the structural and functional impact of sulfhydryl modification is essential.

Purpose of the Study:

• To investigate the effects of two sulfhydryl reagents, N-ethylmaleimide (NEM) and diamide, on the skeletal muscle Ca2+ release channel.
• To elucidate the mechanisms by which these reagents modulate channel activity and ligand binding.
• To identify functionally important sulfhydryl groups and potential sites of subunit interaction.

Main Methods:

• Reconstitution of the skeletal muscle Ca2+ release channel into planar lipid bilayers.
• Functional assays measuring channel activity and [3H]ryanodine binding.
• Analysis of subunit cross-linking induced by diamide and its modulation by NEM.

Main Results:

• NEM exhibits a triphasic effect on channel activity and ryanodine binding: inhibition, activation, then inhibition.
• Diamide activates the channel, enhances ryanodine binding, and induces inter-subunit cross-linking, which is reversible by dithiothreitol.
• Diamide protects against NEM's initial inhibitory phase, suggesting it modifies or masks critical sulfhydryl sites.

Conclusions:

• Diamide's effects suggest it either cross-links specific sulfhydryl groups or induces a conformational change affecting NEM accessibility.
• The findings provide a basis for mapping subunit contact sites and identifying key sulfhydryl residues in the Ca2+ release channel.
• This research contributes to understanding the regulation of skeletal muscle excitation-contraction coupling.