Ryanodine

BackgroundAging is associated with an increased incidence of atrioventricular nodal (AVN) dysfunction.ObjectiveThe aim of this study was to investigate the structural and functional remodeling in the atrioventricular junction (AVJ) with aging.MethodsElectrophysiology, histology, and immunohistochemistry experiments on male Wistar Hannover rats aged 3 months (n = 24) and 2 years (n = 15) were performed. Atrio-His (AH) interval, Wenkebach cycle length (WBCL), and AVN effective refractory period (AVNERP) were measured. Cesium (2 mM) was used to block hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, while ryanodine (2 μM) was used to block ryanodine 2 (RyR2) channels. Protein expression from different regions of the AVJ was studied using immunofluorescence. The expression of connexins (connexin 43 and connexin 40), ion channels (Hyperpolarization-activated cyclic nucleotide-gated channel 4 (HCN4), voltage sensitive sodium channel (Nav1.5), and L-Type calcium channel (Cav1.3)), and calcium handling proteins (RyR2 and sarco/endoplasmic reticulum calcium ATPaset type 2a (SERCA2a)) were measured. Morphological characteristics were studied with histology.ResultsWithout drugs to block HCN and RyR2 channels, there was prolongation of the AH interval, WBCL, and AVNERP (P v1.5, and RyR2 downregulate in the regions of the AVJ and connexin 40, SERCA2a, and Cav1.3 upregulate (P ConclusionHeterogeneous ion channel expression changes were observed in the AVJ with aging. For the first time, we have shown that HCN and RyR2 play an important role in AVN dysfunction with aging.

The roles of Ca2+-induced calcium release in synaptic plasticity and metaplasticity are poorly understood. The present study has addressed the role of intracellular Ca2+ stores in long-term potentiation (LTP) and a form of heterosynaptic metaplasticity known as synaptic tagging and capture (STC) at CA1 synapses in mouse hippocampal slices. The effects of two compounds, ryanodine and cyclopiazonic acid (CPA), were examined on LTP induced by three distinct induction protocols: weak (w), compressed (c) and spaced (s) theta-burst stimulation (TBS). These compounds did not significantly affect LTP induced by the wTBS (one episode of TBS; 25 stimuli) or cTBS (three such episodes with a 10 s inter-episode interval (IEI); 75 stimuli) but substantially inhibited LTP induced by a sTBS (10 min IEI; 75 stimuli). Ryanodine and CPA also prevented a small heterosynaptic potentiation that was observed with the sTBS protocol. Interestingly, these compounds also prevented STC when present during either the sTBS or the subsequent wTBS, applied to an independent input. All of these effects of ryanodine and CPA were similar to that of a calcium-permeable AMPA receptor blocker. In conclusion, Ca2+ stores provide one way in which signals are propagated between synaptic inputs and, by virtue of their role in STC, may be involved in associative long-term memories. This article is part of a discussion meeting issue 'Long-term potentiation: 50 years on'.

AimsThe cardiac ryanodine receptor (RyR2), which mediates intracellular Ca2+ release to trigger cardiomyocyte contraction, participates in development of acquired and inherited arrhythmogenic cardiac disease. This study was undertaken to characterize the network of inter- and intra-subunit interactions regulating the activity of the RyR2 homotetramer.Methods and resultsWe use mutational investigations combined with biochemical assays to identify the peptide sequence bridging the β8 with β9 strand as the primary determinant mediating RyR2 N-terminus self-association. The negatively charged side chains of two aspartate residues (D179 and D180) within the β8-β9 loop are crucial for the N-terminal inter-subunit interaction. We also show that the RyR2 N-terminus domain interacts with the C-terminal channel pore region in a Ca2+-independent manner. The β8-β9 loop is required for efficient RyR2 subunit oligomerization but it is dispensable for N-terminus interaction with C-terminus. Deletion of the β8-β9 sequence produces unstable tetrameric channels with subdued intracellular Ca2+ mobilization implicating a role for this domain in channel opening. The arrhythmia-linked R176Q mutation within the β8-β9 loop decreases N-terminus tetramerization but does not affect RyR2 subunit tetramerization or the N-terminus interaction with C-terminus. RyR2R176Q is a characteristic hypersensitive channel displaying enhanced intracellular Ca2+ mobilization suggesting an additional role for the β8-β9 domain in channel closing.ConclusionThese results suggest that efficient N-terminus inter-subunit communication mediated by the β8-β9 loop may constitute a primary regulatory mechanism for both RyR2 channel activation and suppression.

Awareness of new potential doping agents and the proactive implementation of detection methods are key aspects of preventive antidoping research. Ryanodine receptor-1-calstabin complex stabilizers (RYR-stabilizers) are a novel class of drug candidates for the treatment of various diseases associated with leaky Ca2+ channels in the cardiac or skeletal muscle. Also, intense physical activity was shown to transiently cause leakage of skeletal muscle Ca2+ channels, and RYR-stabilizers have been shown to restore normal activity and, thus, increase endurance performance. Consequently, such compounds are relevant targets in doping controls, and to date, in particular, compounds S107, JTV-519, ARM 036, and ARM 210 have been subject of antidoping research. In this study, ARM 036 and ARM 210 as well as the commercially available compounds S107 and JTV-519 were synthesized using a multistep approach. Subsequently, all compounds were investigated concerning their in vitro metabolic behavior, and various metabolites were identified. Selected metabolites were then chemically synthesized for comprehensive structure confirmation. The findings of this study will contribute to routine doping control analytical programs and allow for improving existing detection methods.