Aims: 

In cardiac muscle, the intracellular trigger for contraction is a transient rise in intracellular free Ca²⁺ released from the sarcoplasmic reticulum (SR) through a major intracellular Ca²⁺ channel - ryanodine receptor (RYR). Two or more RYR channels reconstituted into bilayer lipid membrane (BLM) can open and close either independently (single gating) or simultaneously (coupled gating). The coupled gating phenomenon has been suggested as an attractive candidate for a termination mechanism of Ca²⁺ release from the SR required for periodic contraction and relaxation of cardiac muscle.

Methods: 

Using the method of reconstitution of a channel into BLM we investigated the potential effect of luminal Ca²⁺ on the stability of coupling between RYR channels isolated from the rat heart. We introduced a parameter of coupling stability for each detected simultaneous opening and closing and further averaged for experiments performed under identical conditions.

Results: 

We found that the stability of coupling during simultaneous opening of RYR channels was significantly lower in comparison to the simultaneous closing under same experimental conditions. Furthermore, high concentration of luminal Ca²⁺ (53mM) as well as the absence of luminal Ca²⁺ noticeable destabilized functional coupling between RYR channels during opening, in contrast to lower tested concentrations (8mM-20mM).

Conclusion: 

We provided experimental evidence that the stability of coupling between RYR channels depends on the functional state of channels. Furthermore, we pointed for the first time to the regulation role of luminal Ca²⁺ in the strength of interaction between coupled RYR channels in the heart.

Supported by grant VEGA 2/6011/26.