Membrane depolarization increases ryanodine sensitivity to Ca²⁺ release to the cytosol in L6 skeletal muscle cells: Implications for excitation–contraction coupling

Abstract

The dihydropyridine receptor in the plasma membrane and the ryanodine receptor in the sarcoplasmic reticulum are known to physically interact in the process of excitation-contraction coupling. However, the mechanism for subsequent Ca 2þ release through the ryanodine receptor is unknown. Our lab has previously presented evidence that the dihydropyridine receptor and ryanodine receptor combine as a channel for the entry of Ca 2þ under resting conditions, known as store operated calcium entry.Here, we provide evidence that depolarization during excitation-contraction coupling causes the dihydropyridine receptor to disengage from the ryanodine receptor. The newly freed ryanodine receptor can then transport Ca 2þ from the sarcoplasmic reticulum to the cytosol. Experimentally, this should more greatly expose the ryanodine receptor to exogenous ryanodine. To examine this hypothesis, we titrated L6 skeletal muscle cells with ryanodine in resting and excited (depolarized) states. When L6 muscle cells were depolarized with high potassium or exposed to the dihydropyridine receptor agonist BAYK-8644, known to induce dihydropyridine receptor movement within the membrane, ryanodine sensitivity was enhanced. However, ryanodine sensitivity was unaffected when Ca 2þ was elevated without depolarization by the ryanodine receptor agonist chloromethylcresol, or by increasing Ca 2þ concentration in the media. Ca 2þ entry currents (from the extracellular space) during excitation were strongly inhibited by ryanodine, but Ca 2þ entry currents in the resting state were not. We conclude that excitation releases the ryanodine receptor from occlusion by the dihydropyridine receptor, enabling Ca 2þ release from the ryanodine receptor to the cytosol.

Alzheimer’s Disease Presenilin-1 Mutation Sensitizes Neurons to Impaired Autophagy Flux and Propofol Neurotoxicity: Role of Calcium Dysregulation

“…However, abnormal and excessive Ca 2+ release from the ER via InsP 3 Rs/RYRs may result in impaired autophagy, mitochondria damage, cell arrest and death [41], which may be the mechanism of some pathology in neurodegenerative diseases [42]. It has been demonstrated that both InsP 3 Rs and RYRs are excessively activated in AD due to abnormally increased receptor numbers [43], and the elevated receptor hypersensitivity to their agonists [44]. Abnormal and excessive Ca 2+ release from the ER not only dangerously increases [Ca 2+ ] c but also detrimentally decreases ER calcium contents.…”

ERG1a K+Channel Increases Intracellular Calcium Concentration through Modulation of Calsequestrin 1 in C2C12Myotubes

“…Ryanodine Receptor Activation with Caffeine. Membrane depolarization will uncouple RYR1 from occlusion by the DHPR and allow Ca 2+ release from the SR to the cytosol through the RYR1 channel (Pitake and Ochs 2015); therefore, we determined if HERG affects RYR1 activity specifically. Thus, RYR1 activity was assayed in control and HERG-expressing myotubes using caffeine to activate the RYR1 and the area under the curve (AUC) of the rise in [Ca 2+ ] i was determined for each treatment group.…”

“…al., 2004; Lyfenko & Dirksen 2008 in Dirksen 2009). The cells were then depolarized: 1) to release RYR1 from occlusion by Ca v 1.1 (i.e., DHPR) and enable Ca 2+ release from the SR to the cytosol through the RYR1 channel (Pitake and Ochs 2015); and 2) to inhibit SOCE (Stiber et. al., 2008 in Dirksen 2009; Kurebayashi & Ogawa 2001).…”

“…It is reported that RYR1 is voltage-activated (Nelson et. al., 2013) and that membrane depolarization will release RYR1 from occlusion by the DHPR and allow Ca 2+ release from the SR to the cytosol through the RYR1 channel (Pitake and Ochs 2015). Indeed, expression of HERG did enhance the increase in [Ca 2+ ] i that occurs with caffeine treatment in myotubes, and this effect was blocked by ryanodine, indicating HERG-modulation of RYR1.…”

Aloperine Relieves Type 2 Diabetes Mellitus via Enhancing GLUT4 Expression and Translocation

“…We found that 2-APB significantly inhibited ALO-induced increase of IRAP fluorescence intensity at the PM and intracellular Ca 2+ under 2 mM ( Figure 5A ) and 0 mM ( Figure 5B ) extracellular Ca 2+ conditions. In addition to IP 3 R, Ryanodine receptor (RyR) is also an important receptor that regulates intracellular calcium release ( Pitake and Ochs, 2016 ). Therefore, we studied the effect of RyR on ALO-induced intracellular Ca 2+ and GLUT4 trafficking to the PM.…”