Voltage-Dependent Modulation of Cardiac Ryanodine Receptors (RyR2) by Protamine

• Published in: PloS one Vol. 4; no. 12; p. e8315
• Main Authors: Diaz-Sylvester, Paula L., Copello, Julio A.
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 15.12.2009; Public Library of Science (PLoS)
• Subjects: Activation; Animals; Anticoagulants; Biophysics/Biomacromolecule-Ligand Interactions; Biophysics/Membrane Proteins and Energy Transduction; Calcium (reticular); Calcium - metabolism; Calcium channels; Cardiac muscle; Channel gating; Conductance; Coronary artery disease; Cytosol; Cytosol - drug effects; Cytosol - metabolism; Electric Conductivity; Electric potential; Electrostatic properties; Heart diseases; Histones; Ion Channel Gating - drug effects; Laboratory animals; Leak channels; Ligands; Lipid bilayers; Lipids; Magnesium; Microsomes; Modulation; Musculoskeletal system; Myocardium - metabolism; Physiology/Cardiovascular Physiology and Circulation; Physiology/Cell Signaling; Physiology/Membranes and Sorting; Physiology/Muscle and Connective Tissue; Polycations; Protamine; Protamines - pharmacology; Proteins; Receptors; Resistance; Rodents; Ryanodine Receptor Calcium Release Channel - metabolism; Ryanodine receptors; Sarcoplasmic reticulum; Scorpion Venoms - pharmacology; Sus scrofa; Voltage; United States > US; Illinois
• DOI: 10.1371/journal.pone.0008315
• ISSN: 1932-6203

It has been reported that protamine (>10 microg/ml) blocks single skeletal RyR1 channels and inhibits RyR1-mediated Ca2+ release from sarcoplasmic reticulum microsomes. We extended these studies to cardiac RyR2 reconstituted into planar lipid bilayers. We found that protamine (0.02-20 microg/ml) added to the cytosolic surface of fully activated RyR2 affected channel activity in a voltage-dependent manner. At membrane voltage (V(m); SR lumen-cytosol) = 0 mV, protamine induced conductance transitions to several intermediate states (substates) as well as full block of RyR2. At V(m)>10 mV, the substate with the highest level of conductance was predominant. Increasing V(m) from 0 to +80 mV, decreased the number of transitions and residence of the channel in this substate. The drop in current amplitude (full opening to substate) had the same magnitude at 0 and +80 mV despite the approximately 3-fold increase in amplitude of the full opening. This is more similar to rectification of channel conductance induced by other polycations than to the action of selective conductance modifiers (ryanoids, imperatoxin). A distinctive effect of protamine (which might be shared with polylysines and histones but not with non-peptidic polycations) is the activation of RyR2 in the presence of nanomolar cytosolic Ca2+ and millimolar Mg2+ levels. Our results suggest that RyRs would be subject to dual modulation (activation and block) by polycationic domains of neighboring proteins via electrostatic interactions. Understanding these interactions could be important as such anomalies may be associated with the increased RyR2-mediated Ca2+ leak observed in cardiac diseases.