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

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Item Type:	Article
Title:	Ahnak is critical for cardiac Ca(v)1.2 calcium channel function and its beta-adrenergic regulation
Creators Name:	Haase, H., Alvarez, J., Petzhold, D., Doller, A., Behlke, J., Erdmann, J., Hetzer, R., Regitz-Zagrosek, V., Vassort, G. and Morano, I.
Abstract:	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.
Keywords:	Recombinant Protein, Missense Variant, beta 2 Subunit, Binding Affinity
Source:	FASEB Journal
ISSN:	0892-6638
Publisher:	Federation of American Societies for Experimental Biology
Volume:	19
Number:	14
Page Range:	1969-1977
Date:	December 2005
Official Publication:	https://doi.org/10.1096/fj.05-3997com
PubMed:	View item in PubMed

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