Ryanodine receptors (RyRs) of skeletal muscle, as calcium release channels, have been found to form semicrystalline arrays in the membrane of sarcoplasmic reticulum. Recently, both experimental observations and theoretical simulations suggested cooperative coupling within interlocking RyRs. To better understand the interactions between RyRs and their modulation, the aggregation and dissociation of isolated RyRs in aqueous medium containing various Na(+) and K(+) concentrations were investigated using photon correlation spectroscopy (PCS) and atomic force microscopy (AFM). RyRs aggregated readily at low salt concentrations. However, a different behavior was observed in the presence of Na(+) or K(+). Detectable aggregates were formed in 5 microg/mL RyR sample when the concentration of Na(+) and K(+) was reduced from 1 M to below 0.28 and 0.23 M, respectively. The dissociation of RyR aggregates was also examined when raising the salt concentration. While aggregates formed in 0.15 M NaCl medium could reverse almost completely, those formed in 0.15 M KCl medium only dissolved partly. When keeping the total salt concentration at 0.15 M, the aggregation and dissociation of RyRs were seen to evidently depend on the relative concentration of Na(+) and K(+). The interaction between RyRs was strengthened with increasing Na(+)/K(+) ratios in the mixed medium. Accompanying this, a decrease of [(3)H]ryanodine binding occurred. The results obtained with PCS and AFM provide further evidence for the interaction between RyRs and suggest the importance of Na(+), K(+), and their relative composition in modulating the interaction and cooperation between RyRs in vivo.

The calcium release channels/ryanodine receptors (RyRs) usually form two-dimensional regular lattices in the endoplasmic/sarcoplasmic reticulum membranes. However, the function and modulation of the interaction between neighboring RyRs are still unknown. Here, with an in vitro aqueous system, we demonstrate that the interaction between RyRs isolated from skeletal muscle (RyR1s) is modulated by their functional states by using photon correlation spectroscopy and [(3)H]ryanodine binding assay. High level of oligomerization is observed for resting closed RyR1s with nanomolar Ca(2+) in solution. Activation of RyR1s by micromolar Ca(2+) or/and millimolar AMP leads to the de-oligomerization of RyR1s. The oligomerization of RyR1s remains at high level when RyR1s are stabilized at closed state by Mg(2+). The modulation of RyR1-RyR1 interaction by the functional state is also observed under near-physiological conditions, suggesting that the interaction between arrayed RyR1s would be dynamically modulated during excitation-contraction coupling. These findings provide exciting new information to understand the function and operating mechanism of RyR arrays.