Ahnak is critical for cardiac Ca(V)1.2 calcium channel function and its beta-adrenergic regulation

FASEB J. 2005 Dec;19(14):1969-77. doi: 10.1096/fj.05-3997com.


Defective L-type Ca2+ channel (I(CaL)) regulation is one major cause for contractile dysfunction in the heart. The I(CaL) is enhanced by sympathetic nervous stimulation: via the activation of beta-adrenergic receptors, PKA phosphorylates the alpha1C(Ca(V)1.2)- and beta2-channel subunits and ahnak, an associated 5643-amino acid (aa) protein. In this study, we examined the role of a naturally occurring, genetic variant Ile5236Thr-ahnak on I(CaL). Binding experiments with ahnak fragments (wild-type, Ile5236Thr mutated) and patch clamp recordings revealed that Ile5236Thr-ahnak critically affected both beta2 subunit interaction and I(CaL) regulation. Binding affinity between ahnak-C1 (aa 4646-5288) and beta2 subunit decreased by approximately 50% after PKA phosphorylation or in the presence of Ile5236Thr-ahnak peptide. On native cardiomyocytes, intracellular application of this mutated ahnak peptide mimicked the PKA-effects on I(CaL) increasing the amplitude by approximately 60% and slowing its inactivation together with a leftward shift of its voltage dependency. Both mutated Ile5236Thr-peptide and Ile5236Thr-fragment (aa 5215-5288) prevented specifically the further up-regulation of I(CaL) by isoprenaline. Hence, we suggest the ahnak-C1 domain serves as physiological brake on I(CaL). Relief from this inhibition is proposed as common pathway used by sympathetic signaling and Ile5236Thr-ahnak fragments to increase I(CaL). This genetic ahnak variant might cause individual differences in I(CaL) regulation upon physiological challenges or therapeutic interventions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / chemistry
  • Calcium Channels, L-Type / chemistry
  • Calcium Channels, L-Type / metabolism
  • Calcium Channels, L-Type / physiology*
  • Cardiomyopathy, Hypertrophic / genetics
  • Cyclic AMP-Dependent Protein Kinases / chemistry
  • Cyclic AMP-Dependent Protein Kinases / metabolism
  • Dose-Response Relationship, Drug
  • Electrophysiology
  • Female
  • Gene Expression Regulation
  • Genetic Variation
  • Glutathione Transferase / metabolism
  • Heterozygote
  • Humans
  • Isoleucine / chemistry
  • Male
  • Membrane Proteins / genetics
  • Membrane Proteins / physiology*
  • Models, Biological
  • Models, Genetic
  • Mutation
  • Mutation, Missense
  • Myocardium / metabolism
  • Myocytes, Cardiac / metabolism
  • Neoplasm Proteins / genetics
  • Neoplasm Proteins / physiology*
  • Peptides / chemistry
  • Phosphorylation
  • Polymorphism, Genetic
  • Polymorphism, Single-Stranded Conformational
  • Protein Binding
  • Protein Structure, Tertiary
  • Rats
  • Rats, Wistar
  • Receptors, Adrenergic, beta / metabolism*
  • Recombinant Proteins / chemistry
  • Software
  • Temperature
  • Threonine / chemistry
  • Ultracentrifugation
  • Up-Regulation


  • AHNAK protein, human
  • Calcium Channels, L-Type
  • L-type calcium channel alpha(1C)
  • Membrane Proteins
  • Neoplasm Proteins
  • Peptides
  • Receptors, Adrenergic, beta
  • Recombinant Proteins
  • Isoleucine
  • Threonine
  • Glutathione Transferase
  • Cyclic AMP-Dependent Protein Kinases
  • Calcium