Modification of cardiac Ca2+ release channel gating by DIDS

Area of Science:

• Cardiovascular Physiology
• Ion Channel Biophysics
• Molecular Pharmacology

Background:

• Cardiac sarcoplasmic reticulum Ca2+ release channels (ryanodine receptors) are critical for excitation-contraction coupling.
• Modulation of these channels by small molecules can profoundly impact cardiac function.
• Understanding channel gating mechanisms is essential for developing targeted therapeutics.

Purpose of the Study:

• To investigate the effects of 4,4 '-diisothiocyanatostilbene-2,2 '-disulfonic acid (DIDS) on cardiac sarcoplasmic reticulum Ca2+ release channels.
• To characterize the gating properties of DIDS-modified channels in a controlled experimental system.

Main Methods:

• Single channel recordings of cardiac sarcoplasmic reticulum Ca2+ release channels reconstituted into planar lipid bilayers.
• Application of DIDS to the cis (cytoplasmic) side of the channel.
• Analysis of channel open probability, dwell times, and voltage dependence.

Main Results:

• DIDS induced a rapid, step-like increase in channel open probability (Po), with a 15-fold steady-state increase at zero holding potential.
• DIDS stabilized a long-lived open state, with distinct kinetics at different membrane potentials (0 mV vs. -50 mV).
• Voltage-induced changes in modified channel activity were reversible, occurring faster than DIDS activation, and channel conductance remained unchanged, suggesting covalent modification of gating components.

Conclusions:

• DIDS acts as a potent activator of cardiac sarcoplasmic reticulum Ca2+ release channels.
• The observed effects are consistent with a covalent modification of an amino group within the channel's gating machinery.
• This study provides insights into the structural basis of channel gating and potential targets for pharmacological intervention.