Biomedical subjects

M Gaburjakova

Publications and source records attributed to M Gaburjakova.

6 recordsLinked to original sources

PubMed2001

beta-adrenergic receptor blockers restore cardiac calcium release channel (ryanodine receptor) structure and function in heart failure.

BACKGROUND: beta-Adrenergic receptor blockade is one of the most effective treatments for heart failure, a leading cause of mortality worldwide. The use of beta-adrenergic receptor blockers in patients with heart failure is counterintuitive, however, because they are known to decrease contractility in normal hearts. The ryanodine receptor (RyR2) on cardiac sarcoplasmic reticulum is the key calcium release channel required for excitation-contraction coupling. In failing hearts, the stoichiometry and function of the RyR2 macromolecular complex is altered. Decreased levels of phosphatases (PP1 and PP2A) and hyperphosphorylation by protein kinase A result in dissociation of the regulatory protein FKBP12.6 and channels with increased open probability. METHODS AND RESULTS: Here, we show that systemic oral administration of a beta-adrenergic receptor blocker reverses protein kinase A hyperphosphorylation of RyR2, restores the stoichiometry of the RyR2 macromolecular complex, and normalizes single-channel function in a canine model of heart failure. CONCLUSIONS: These results may, in part, explain the improved cardiac function observed in heart failure patients treated with beta-adrenergic receptor blockers.

Adrenergic beta-Antagonists↗

PubMed2001

Dilated cardiomyopathy and sudden death resulting from constitutive activation of protein kinase a.

beta-Adrenergic receptor (betaAR) signaling, which elevates intracellular cAMP and enhances cardiac contractility, is severely impaired in the failing heart. Protein kinase A (PKA) is activated by cAMP, but the long-term physiological effect of PKA activation on cardiac function is unclear. To investigate the consequences of chronic cardiac PKA activation in the absence of upstream events associated with betaAR signaling, we generated transgenic mice that expressed the catalytic subunit of PKA in the heart. These mice developed dilated cardiomyopathy with reduced cardiac contractility, arrhythmias, and susceptibility to sudden death. As seen in human heart failure, these abnormalities correlated with PKA-mediated hyperphosphorylation of the cardiac ryanodine receptor/Ca(2+)-release channel, which enhances Ca(2+) release from the sarcoplasmic reticulum, and phospholamban, which regulates the sarcoplasmic reticulum Ca(2+)-ATPase. These findings demonstrate a specific role for PKA in the pathogenesis of heart failure, independent of more proximal events in betaAR signaling, and support the notion that PKA activity is involved in the adverse effects of chronic betaAR signaling.

Animals↗

PubMed2001

Coupled gating between cardiac calcium release channels (ryanodine receptors).

Excitation-contraction coupling in heart muscle requires the activation of Ca(2+)-release channels/type 2 ryanodine receptors (RyR2s) by Ca(2+) influx. RyR2s are arranged on the sarcoplasmic reticular membrane in closely packed arrays such that their large cytoplasmic domains contact one another. We now show that multiple RyR2s can be isolated under conditions such that they remain physically coupled to one another. When these coupled channels are examined in planar lipid bilayers, multiple channels exhibit simultaneous gating, termed "coupled gating." Removal of the regulatory subunit, the FK506 binding protein (FKBP12.6), functionally but not physically uncouples multiple RyR2 channels. Coupled gating between RyR2 channels may be an important regulatory mechanism in excitation-contraction coupling as well as in other signaling pathways involving intracellular Ca(2+) release.

Animals↗

PubMed2001

Phosphorylation-dependent regulation of ryanodine receptors: a novel role for leucine/isoleucine zippers.

Ryanodine receptors (RyRs), intracellular calcium release channels required for cardiac and skeletal muscle contraction, are macromolecular complexes that include kinases and phosphatases. Phosphorylation/dephosphorylation plays a key role in regulating the function of many ion channels, including RyRs. However, the mechanism by which kinases and phosphatases are targeted to ion channels is not well understood. We have identified a novel mechanism involved in the formation of ion channel macromolecular complexes: kinase and phosphatase targeting proteins binding to ion channels via leucine/isoleucine zipper (LZ) motifs. Activation of kinases and phosphatases bound to RyR2 via LZs regulates phosphorylation of the channel, and disruption of kinase binding via LZ motifs prevents phosphorylation of RyR2. Elucidation of this new role for LZs in ion channel macromolecular complexes now permits: (a) rapid mapping of kinase and phosphatase targeting protein binding sites on ion channels; (b) predicting which kinases and phosphatases are likely to regulate a given ion channel; (c) rapid identification of novel kinase and phosphatase targeting proteins; and (d) tools for dissecting the role of kinases and phosphatases as modulators of ion channel function.

Amino Acid Sequence↗

PubMed2001

FKBP12 binding modulates ryanodine receptor channel gating.

The ryanodine receptor (RyR1)/calcium release channel on the sarcoplasmic reticulum of skeletal muscle is comprised of four 565,000-dalton RyR1s, each of which binds one FK506 binding protein (FKBP12). RyR1 is required for excitation-contraction coupling in skeletal muscle. FKBP12, a cis-trans peptidyl-prolyl isomerase, is required for the normal gating of the RyR1 channel. In the absence of FKBP12, RyR1 channels exhibit increased gating frequency, suggesting that FKBP12 "stabilizes" the channel in the open and closed states. We now show that substitution of a Gly, Glu, or Ile for Val2461 in RyR1 prevents FKBP12 binding to RyR1, resulting in channels with increased gating frequency. In the case of the V2461I mutant RyR1, normal channel function can be restored by adding FKBP12.6, an isoform of FKBP12. These data identify Val2461 as a critical residue required for FKBP12 binding to RyR1 and demonstrate the functional role for FKBP12 in the RyR1 channel complex.

Amino Acid Sequence↗

PubMed1998

FKBP12 modulates gating of the ryanodine receptor/calcium release channel.

Excitation-contraction (EC) coupling in muscle requires the activation of intracellular calcium release channels (CRC). Four type 1 ryanodine receptor (RyR1) molecules form each tetrameric CRC. Each RyR1 contains a binding site for the FK506 binding protein (FKBP12), a cis-trans peptidyl-prolyl isomerase that is required for coordinated gating of the four RyR1 subunits comprising the channel. When FKBP12 is bound to RyR1, it stabilizes the four subunits that form each CRC. We propose that binding of one FKBP12 to each RyR1 lowers the energy of twisted-amide peptidyl-prolyl bonds and stabilizes RyR1 in a conformation that permits coordinated gating of the four RyR1 subunits.

Animals↗