PKA phosphorylation activates the calcium release channel (ryanodine receptor) in skeletal muscle

Abstract

The type 1 ryanodine receptor (RyR1) on the sarcoplasmic reticulum (SR) is the major calcium (Ca2+) release channel required for skeletal muscle excitation–contraction (EC) coupling. RyR1 function is modulated by proteins that bind to its large cytoplasmic scaffold domain, including the FK506 binding protein (FKBP12) and PKA. PKA is activated during sympathetic nervous system (SNS) stimulation. We show that PKA phosphorylation of RyR1 at Ser2843 activates the channel by releasing FKBP12. When FKB12 is bound to RyR1, it inhibits the channel by stabilizing its closed state. RyR1 in skeletal muscle from animals with heart failure (HF), a chronic hyperadrenergic state, were PKA hyperphosphorylated, depleted of FKBP12, and exhibited increased activity, suggesting that the channels are “leaky.” RyR1 PKA hyperphosphorylation correlated with impaired SR Ca2+ release and early fatigue in HF skeletal muscle. These findings identify a novel mechanism that regulates RyR1 function via PKA phosphorylation in response to SNS stimulation. PKA hyperphosphorylation of RyR1 may contribute to impaired skeletal muscle function in HF, suggesting that a generalized EC coupling myopathy may play a role in HF.

Ryanodine receptor type 1 gene mutations found in the Canadian malignant hyperthermia population

“…release channel function through serine phosphorylation. 41,42 The second mutation, p.Gly4935Ser, identified in an MHS first-degree relative of the proband who had a fatal MH crisis, maps to the centre of the last transmembrane segment (amino acids 4918-4948) within the pore-forming region of RyR1 38 and a mutation hot spot, HS3b, where disease-associated mutations occur at a rate of about one in every three amino acids. 13 Furthermore, the p.Gly4935Ser was recently reported to be associated with MH in a large Brazilian pedigree.…”

Ryanodine Receptors: Structure, Expression, Molecular Details, and Function in Calcium Release

“…They also suggest that hyperphosphorylation causes FKBPs to dissociate from RyRs, producing "leaky channels" (i.e., channels prone to open at rest). Such leaky channels could underlie increased risk for arrhythmias in heart failure and contribute to decreased muscle force production by reducing SR Ca 2þ store content (Marx et al 2000;Reiken et al 2003). However, other groups have not found PKA-dependent hyperphosphorylation in failing hearts (Xiao et al 2005).…”

“…SNS activation causes b-adrenergic stimulation of the muscle, which via an intracellular signaling cascade results in activation of PKA. SNS-activated PKA phosphorylates RyR, altering its gating properties, but also phosphorylates several other key proteins involved in Ca 2þ handling such as troponin I and phospholamban (Valdivia et al 1995;Li et al 2000;Kentish et al 2001;Reiken et al 2003). Modified RyR function is associated with increased SR Ca 2þ leak in heart, which could contribute to reduced contractile function and increased propensity to arrhythmias.…”

Functional Consequences of Phosphomimetic Mutations at Key cAMP-dependent Protein Kinase Phosphorylation Sites in the Type 1 Inositol 1,4,5-Trisphosphate Receptor

“…This charge neutralization, in turn, is thought to result in a conformational change in the protein. A common approach employed to investigate the functional effects of phosphorylation is to construct phosphomimetic mutations whereby glutamic or aspartic acid residues are substituted at the phosphoacceptor site (31,32). The rationale for this strategy is that the negatively charged side chain of the substituted acidic amino acid will mimic, to an extent, the addition of a phosphate moiety to the protein.…”