Modulation of cardiac ryanodine receptor channels by alkaline earth cations

• Published in: PloS one 2011-10, Vol.6 (10), p.e26693-e26693
• Main Authors: Diaz-Sylvester, Paula L, Porta, Maura, Copello, Julio A
• Format: Article
• Language: English
• Subjects: Activation; Affinity; Animals; Binding Sites; Biology; Caffeine; Caffeine - pharmacology; Calcium; Calcium-binding protein; Cations; Channel gating; Channel opening; Current carriers; Cytosol - metabolism; Divalent cations; Electric potential; Heart; Heart diseases; Kinetics; Laboratory animals; Lipids; Magnesium; Medicine; Musculoskeletal system; Myocardium - metabolism; Physics; Receptor channels; Rodents; Ryanodine Receptor Calcium Release Channel - metabolism; Ryanodine receptors; Sarcoplasmic Reticulum - metabolism; Swine; Ventricle; Voltage
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0026693

Cardiac ryanodine receptor (RyR2) function is modulated by Ca(2+) and Mg(2+). To better characterize Ca(2+) and Mg(2+) binding sites involved in RyR2 regulation, the effects of cytosolic and luminal earth alkaline divalent cations (M(2+): Mg(2+), Ca(2+), Sr(2+), Ba(2+)) were studied on RyR2 from pig ventricle reconstituted in bilayers. RyR2 were activated by M(2+) binding to high affinity activating sites at the cytosolic channel surface, specific for Ca(2+) or Sr(2+). This activation was interfered by Mg(2+) and Ba(2+) acting at low affinity M(2+)-unspecific binding sites. When testing the effects of luminal M(2+) as current carriers, all M(2+) increased maximal RyR2 open probability (compared to Cs(+)), suggesting the existence of low affinity activating M(2+)-unspecific sites at the luminal surface. Responses to M(2+) vary from channel to channel (heterogeneity). However, with luminal Ba(2+)or Mg(2+), RyR2 were less sensitive to cytosolic Ca(2+) and caffeine-mediated activation, openings were shorter and voltage-dependence was more marked (compared to RyR2 with luminal Ca(2+)or Sr(2+)). Kinetics of RyR2 with mixtures of luminal Ba(2+)/Ca(2+) and additive action of luminal plus cytosolic Ba(2+) or Mg(2+) suggest luminal M(2+) differentially act on luminal sites rather than accessing cytosolic sites through the pore. This suggests the presence of additional luminal activating Ca(2+)/Sr(2+)-specific sites, which stabilize high P(o) mode (less voltage-dependent) and increase RyR2 sensitivity to cytosolic Ca(2+) activation. In summary, RyR2 luminal and cytosolic surfaces have at least two sets of M(2+) binding sites (specific for Ca(2+) and unspecific for Ca(2+)/Mg(2+)) that dynamically modulate channel activity and gating status, depending on SR voltage.