Control of Ca2+ Release by Action Potential Configuration in Normal and Failing Murine Cardiomyocytes

Abstract

Cardiomyocytes from failing hearts exhibit spatially nonuniform or dyssynchronous sarcoplasmic reticulum (SR) Ca(2+) release. We investigated the contribution of action potential (AP) prolongation in mice with congestive heart failure (CHF) after myocardial infarction. AP recordings from CHF and control myocytes were included in a computational model of the dyad, which predicted more dyssynchronous ryanodine receptor opening during stimulation with the CHF AP. This prediction was confirmed in cardiomyocyte experiments, when cells were alternately stimulated by control and CHF AP voltage-clamp waveforms. However, when a train of like APs was used as the voltage stimulus, the control and CHF AP produced a similar Ca(2+) release pattern. In this steady-state condition, greater integrated Ca(2+) entry during the CHF AP lead to increased SR Ca(2+) content. A resulting increase in ryanodine receptor sensitivity synchronized SR Ca(2+) release in the mathematical model, thus offsetting the desynchronizing effects of reduced driving force for Ca(2+) entry. A modest nondyssynchronous prolongation of Ca(2+) release was nevertheless observed during the steady-state CHF AP, which contributed to increased time-to-peak measurements for Ca(2+) transients in failing cells. Thus, dyssynchronous Ca(2+) release in failing mouse myocytes does not result from electrical remodeling, but rather other alterations such as T-tubule reorganization.

Analysis of Cav1.2 and Ryanodine Receptor Clusters in Rat Ventricular Myocytes

“…2, C ii), implying that the relative position of the molecules is not determined by chance. Modeling has demonstrated that the relative position of the molecules impacts the gain of ECC (19,20), so grouping Ca 2þ channels together near the center of the RyR cluster should increase the probability that the released Ca 2þ ions will bind with a RyR, ensuring that the couplon is activated. Finally, these results disagree with freeze-fracture analyses suggesting that the molecules occupy roughly the same area in their respective membranes and that Ca v 1.2 is randomly positioned relative to RyR (18).…”

Methods in cardiomyocyte isolation, culture, and gene transfer

“…20–30 minutes before the anesthetization [3, 11–13] to prevent blood clotting and possible myocardial infarction. Animals are anesthetized using either injectable (pentobarbital, ketamine/xylazyne) or inhalable (isoflurane) anesthetics [3, 13, 14]. It has been reported that the use of inhalable anesthetics for small animals such as mice and rats avoids the risk of myocardial ischemia since the onset of anesthesia is rapid with minimal effects on respiration [15].…”

Manipulation of sarcoplasmic reticulum Ca2+ release in heart failure through mechanical intervention

“…A large number of animal (He et al 2001;Benitah et al 2002;Balijepalli et al 2003;Louch et al 2010a) and human (Lyon et al 2009;Crossman et al 2011) studies have demonstrated that one of the principal insults to local CICR in HF is loss of the t-tubules. These regular membrane invaginations relay the action potential to the depth of the cell rapidly, facilitating synchronous Ca 2+ release from the entire cell (Orchard & Brette, 2008).…”