Regulation of the skeletal muscle ryanodine receptor/Ca2+-release channel RyR1 by S-palmitoylation

The ryanodine receptor/Ca(2+)-release channels (RyRs) of skeletal and cardiac muscle are essential for Ca(2+) release from the sarcoplasmic reticulum that mediates excitation-contraction coupling. It has been shown that RyR activity is regulated by dynamic post-translational modifications of Cys residues, in particular S-nitrosylation and S-oxidation. Here we show that the predominant form of RyR in skeletal muscle, RyR1, is subject to Cys-directed modification by S-palmitoylation. S-Palmitoylation targets 18 Cys within the N-terminal, cytoplasmic region of RyR1, which are clustered in multiple functional domains including those implicated in the activity-governing protein-protein interactions of RyR1 with the L-type Ca(2+) channel CaV1.1, calmodulin, and the FK506-binding protein FKBP12, as well as in "hot spot" regions containing sites of mutations implicated in malignant hyperthermia and central core disease. Eight of these Cys have been identified previously as subject to physiological S-nitrosylation or S-oxidation. Diminishing S-palmitoylation directly suppresses RyR1 activity as well as stimulus-coupled Ca(2+) release through RyR1. These findings demonstrate functional regulation of RyR1 by a previously unreported post-translational modification and indicate the potential for extensive Cys-based signaling cross-talk. In addition, we identify the sarco/endoplasmic reticular Ca(2+)-ATPase 1A and the α1S subunit of the L-type Ca(2+) channel CaV1.1 as S-palmitoylated proteins, indicating that S-palmitoylation may regulate all principal governors of Ca(2+) flux in skeletal muscle that mediates excitation-contraction coupling.

Mechanism of spontaneous termination of stable atrial flutter in the canine sterile pericarditis model

BACKGROUND

We tested the hypotheses that spontaneous termination of stable atrial flutter is directly related to spontaneous beat-to-beat cycle length oscillations and that block of the circulating reentrant wave front occurs in an area of slow conduction.

METHODS AND RESULTS

We studied 30 episodes of spontaneous termination of stable atrial flutter induced by atrial stimulation in 11 conscious, nonsedated dogs with sterile pericarditis. Additionally, in 5 dogs, 14 episodes of spontaneous termination of stable atrial flutter were studied with a multisite mapping system to record simultaneously from 190 right atrial electrodes. In the conscious-state studies, atrial flutter cycle length oscillations began 6 +/- 1 (mean +/- SEM) beats before termination in 26 episodes, stable atrial flutter evolved into atrial fibrillation in 3 episodes, and no cycle length change occurred before termination in 1 episode. In the open-chest studies, in all instances, spontaneous oscillations began 7 +/- 1 beats before termination. The only consistent oscillation pattern occurred for the last two beats: a long cycle length (149 +/- 9 milliseconds) followed by a much shorter cycle length (110 +/- 6 milliseconds) (P < .01). Activation maps demonstrated that all cycle length oscillations were explained by changes of conduction in an area(s) of slow conduction in the reentrant circuit. In two instances, the last (short) cycle length was associated with disappearance of an area of slow conduction. In all episodes, the last circulating reentrant wave front blocked in an area of slow conduction in the reentrant circuit. Although not tested, during the last beat, the very early arrival of the circulating reentrant wave front at an area of slow conduction suggests an important role for refractoriness, with head and tail interactions, resulting in block.

CONCLUSIONS

Spontaneous termination of stable atrial flutter in the sterile pericarditis model (1) is preceded by beat-to-beat cycle length oscillations that result from changes in conduction in areas of slow conduction in the reentrant circuit and (2) results from block of the circulating reentrant wave front in an area of slow conduction.

A cardiac potential mapping system

The technical aspects of a multiple-purpose cardiac mapping system are presented. The authors begin with a brief history of hardware and software development and then concentrate on the major problems in acquiring high-quality recordings from the torso surface or from the epicardial surface and on the processing of the signals for display of color maps or other analysis. To achieve the desired adaptability to a variety of cardiac applications and experiments, they incorporated three parallel microprocessors that can record the signals from 240 electrodes and simultaneously provide display and analysis of the incoming cardiac data. While the parallel processors and modular software offer computational and flexibility advantages, the user interacts with an ordinary AT-compatible computer. This discussion is not a survey of the systems used in the many research laboratories or specific cardiac applications but is focused on experience in developing the specific hardware for such a multi-purpose instrument, and less specifically on the software that makes the system easy to use and adaptable to a variety of experimental and clinical situations.