Moderate Calcium Channel Dysfunction in Adult Mice with Inducible Cardiomyocyte-specific Excision of the cacnb2 Gene

Marcel Meissner,Petra Weissgerber,Juan E Camacho Londoño,Jean Prenen,Sabine Link,Sandra Ruppenthal,Jeffery D Molkentin,Peter Lipp,Bernd Nilius,Marc Freichel,Veit Flockerzi

doi:10.1074/jbc.m111.227819

Abstract

The major L-type voltage-gated calcium channels in heart consist of an α1C (Ca(V)1.2) subunit usually associated with an auxiliary β subunit (Ca(V)β2). In embryonic cardiomyocytes, both the complete and the cardiac myocyte-specific null mutant of Ca(V)β2 resulted in reduction of L-type calcium currents by up to 75%, compromising heart function and causing defective remodeling of intra- and extra-embryonic blood vessels followed by embryonic death. Here we conditionally excised the Ca(V)β2 gene (cacnb2) specifically in cardiac myocytes of adult mice (KO). Upon gene deletion, Ca(V)β2 protein expression declined by >96% in isolated cardiac myocytes and by >74% in protein fractions from heart. These latter protein fractions include Ca(V)β2 proteins expressed in cardiac fibroblasts. Surprisingly, mice did not show any obvious impairment, although cacnb2 excision was not compensated by expression of other Ca(V)β proteins or changes of Ca(V)1.2 protein levels. Calcium currents were still dihydropyridine-sensitive, but current density at 0 mV was reduced by <29%. The voltage for half-maximal activation was slightly shifted to more depolarized potentials in KO cardiomyocytes when compared with control cells, but the difference was not significant. In summary, Ca(V)β2 appears to be a much stronger modulator of L-type calcium currents in embryonic than in adult cardiomyocytes. Although essential for embryonic survival, Ca(V)β2 down-regulation in cardiomyocytes is well tolerated by the adult mice.

Highlights

To the plasma membrane and to produce shifts in the voltage dependence of channel activation
From the four mammalian genes coding for CaV␤ subunits, the cacnb2 gene is predominantly expressed in the heart [2]
We show that CaV␤2 protein expression declined by Ͼ96% in isolated cardiomyocytes following gene deletion and, surprisingly, we observed only moderately impaired L-type calcium currents with a Ͻ29% reduction in current density

Summary

Introduction

To the plasma membrane and to produce shifts in the voltage dependence of channel activation. To study the impact of CaV␤2 deletion in the heart of adult animals, we induced excision of the cacnb2 gene in cardiomyocytes of adult mice. We show that CaV␤2 protein expression declined by Ͼ96% in isolated cardiomyocytes following gene deletion and, surprisingly, we observed only moderately impaired L-type calcium currents with a Ͻ29% reduction in current density.

Results

Conclusion