Robust L‐type calcium current expression following heterozygous knockout of the Cav1.2 gene in adult mouse heart

Abstract

Non-technical summary Appropriate regulation of ion channel expression is critical for the maintenance of both electrical stability and normal contractile function in the heart. A classic way to study the robustness of biological systems is to examine the effects of changes in gene dosage. We have studied how the heart responds to changes in the L-type calcium channel gene dosage. Homozygous Cav1.2 knockout in the adult heart is lethal, without compensatory responses in expression of other calcium channel genes. Following heterozygous knockout, Cav1.2 mRNA levels are not buffered, Cav1.2 membrane protein levels are partly buffered and L-type calcium current expression is relatively well buffered. These data are consistent with a passive model of Cav1.2 biosynthesis that includes saturated steps, which act to buffer Cav1.2 protein and L-type calcium current expression. The results suggest that there is little or no homeostatic regulation of calcium current expression in either heterozygous or homozygous knockout mice.Abstract Mechanisms that contribute to maintaining expression of functional ion channels at relatively constant levels following perturbations of channel biosynthesis are likely to contribute significantly to the stability of electrophysiological systems in some pathological conditions. In order to examine the robustness of L-type calcium current expression, the response to changes in Ca 2+ channel Cav1.2 gene dosage was studied in adult mice. Using a cardiac-specific inducible Cre recombinase system, Cav1.2 mRNA was reduced to 11 ± 1% of control values in homozygous floxed mice and the mice died rapidly (11.9 ± 3 days) after induction of gene deletion. In these homozygous knockout mice, echocardiographic analysis showed that myocardial contractility was reduced to 14 ± 1% of control values shortly before death. For these mice, no effective compensatory changes in ion channel gene expression were triggered following deletion of both Cav1.2 alleles, despite the dramatic decay in cardiac function. In contrast to the homozygote knockout mice, following knockout of only one Cav1.2 allele, cardiac function remained unchanged, as did survival. Cav1.2 mRNA expression in the left ventricle of heterozygous knockout mice was reduced to 58 ± 3% of control values and there was a 21 ± 2% reduction in Cav1.2 protein expression. There was no significant reduction in L-type Ca 2+ current density in these mice. The results are consistent with a model of L-type calcium channel biosynthesis in which there are one or more saturated steps, which act to buffer changes in both total Cav1.2 protein and L-type current expression.

Functional Characterization of CaVα2δ Mutations Associated with Sudden Cardiac Death

“…ND means not determined as the signal-to-noise ratio was too small in the absence of Ca V ␣2␦1. (10) tracked by the external HA epitope and the intracellular mCherry tag, respectively. The constitutive mCherry fluorescence was used as an index of Ca V ␣2␦ expression under all conditions for the wild-type protein as well as the Ca V ␣2␦ mutants (see below).…”

“…Its unique role is substantiated by the observation that homozygous knock-out of the CACNA1C gene is lethal (9,10). In addition to initiating the coordinated contraction of the cardiac ventricles, Ca V 1.2 channels are critical to the heart's normal rhythmic activity (8).…”

Decreased cardiac L-type Ca2+ channel activity induces hypertrophy and heart failure in mice

“…Hence, it remains uncertain how these data relate to our observations in α1C -/+ and α1C fl/fl-Cre mice that did show reduced current, α1C protein, and cardiac function. Indeed, Rosati et al recently showed that heart-specific deletion of α1C resulted in reduced cardiac function and early postnatal lethality, although heterozygous deleted mice showed no baseline phenotype in their analysis (33). These disparities notwithstanding, perhaps the most important observations are from clinical trials with Ca 2+ channel antagonists, which failed to show protective effects in patients with heart failure with systolic dysfunction and, in some cases, showed signs of worsening disease and increased mortality (34,35).…”

Autocrine Interleukin-6 Drives Skin-Derived Mesenchymal Stem Cell Trafficking via Regulating Voltage-Gated Ca2+ Channels

“…Ca 21 flow through these channels serves as the second messenger of electrical signaling, initiating intracellular events such as contraction, secretion, synaptic transmission, fertilization, and gene expression [10]. Mice with the inducible knockout of Ca V 1.2, the gene encodes L-type a1C Ca 21 channel, die before day 14.5 postcoitum, and displayed a profound decrease in myocardial contractility [17]. Although it is becoming increasingly clear that Ca 21 signaling plays a fundamental role in the migration of a variety of cell types, such as neutrophils [18], eosinophils [9], neurons [19], fibroblast [20], and smooth muscle cells [21], to our knowledge no study has reported the role of VGCC regulated by IL-6 signaling in MSC trafficking.…”