Reactive disulfide compounds induce Ca2+ release from cardiac sarcoplasmic reticulum

Area of Science:

• Biochemistry
• Molecular Biology
• Cardiovascular Physiology

Background:

• Cardiac sarcoplasmic reticulum (SR) is crucial for regulating intracellular calcium levels.
• Understanding the mechanisms of calcium release from cardiac SR is vital for cardiovascular health.
• Reactive disulfide compounds (RDSs) are known to interact with sulfhydryl groups.

Purpose of the Study:

• To investigate the effect of RDSs, specifically 2,2'dithiodipyridine (2,2' DTDP) and 4,4' dithiodipyridine (4,4' DTDP), on calcium release from canine cardiac SR.
• To elucidate the mechanism by which RDSs induce calcium release and compare it to other known mechanisms.
• To explore the potential of RDSs as tools for identifying proteins involved in cardiac calcium release.

Main Methods:

• Isolated canine cardiac SR vesicles were used to study calcium release.
• Kinetically and quantitatively measured the oxidation of sulfhydryl (SH) sites by RDSs via thiopyridone absorption.
• Investigated the influence of magnesium ions (Mg2+), adenine nucleotides, and reducing agents on RDS-induced calcium efflux.
• Assessed the effect of RDSs on Ca2+ uptake and Ca2+-dependent ATPase activity.

Main Results:

• RDSs (2,2' DTDP and 4,4' DTDP) induced significant Ca2+ release from cardiac SR.
• The Ca2+ release was dependent on ionized Mg2+ and was modulated by adenine nucleotides.
• RDSs selectively oxidized critical sulfhydryl sites, leading to increased Ca2+ permeability and release.
• Reducing agents inhibited RDS-induced Ca2+ efflux, indicating the reversibility of the process.

Conclusions:

• RDSs trigger Ca2+ release from cardiac SR by oxidizing critical sulfhydryl sites on or near the Ca2+ release channel.
• The oxidation of these sites opens the Ca2+ release channel, while reduction closes it.
• RDSs provide a valuable method for covalently labeling and identifying the protein components of the cardiac SR Ca2+ release channel.