Effect of luminal Ca2+on the stability of coupled gating between ryanodine receptors from the rat heart

AIM: Two or more RYR2 channels reconstituted into a 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 sarcoplasmic reticulum, required for periodic contraction and relaxation of cardiac muscle. METHODS: Using the method of reconstitution of a channel into the BLM, we investigated the potential effect of luminal Ca2+on the stability of the interaction between coupled RYR2 channels isolated from the rat heart. We introduced a new parameter - the coupling stability - for each detected simultaneous opening and closing and further averaged values for experiments performed under identical conditions. RESULTS: We found that the coupling stability during simultaneous opening of RYR2 channels was significantly lower in comparison with the simultaneous closing under the same experimental conditions. Furthermore, high concentration of luminal Ca2+ (53 mmol L(-1)) as well as the absence of luminal Ca2+ noticeably destabilized functional coupling between coupled RYR2 channels during opening, in contrast to lower tested concentrations (8-20 mmol L(-1)). CONCLUSIONS: We provide experimental evidence that the strength of interaction between coupled RYR2 channels depends on the functional state of the channels. Furthermore, we show, for the first time, the regulation role of luminal Ca2+ in the inter-RYR2 functional coupling in the rat heart.