Cardiac Calcium Channels Research Articles

Iron Administration Affects Cardiac Calcium Channel Expression in Mice: The Role of Cardiac Calcium Channel Expression in The Heart of Iron Overload Mice Model

BACKGROUND: Iron-overload cardiomyopathy (IOC) is a major comorbidity in patients with chronic repetitive blood transfusion due to myocardial iron uptake that facilitated by calcium channels. As cardiac compensatory mechanism to IOC, we hypothesized the cardiac calcium channels expression would be increased and involved in cardiomyopathy progressivity. This study was aimed to investigate the gene expression of calcium channels in the heart of the iron overload mice model.METHODS: Mice were divided into three groups according to iron administration doses 0, 0.1, and 0.3 mg/day. Systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) were measured for the representation of cardiovascular outcomes. The heart tissues were harvested. Further mRNA levels of L-type calcium channels (LTCCs) and T-type calcium channels (TTCCs) were examined using semi-quantitative PCR. The expressions of cardiac calcium channels and blood pressure among the three groups were compared.RESULTS: The expressions of TTCCs in the two iron-injected groups were higher than the control group (p=0.018). The expressions of LTCCs were not different (p=0.413) among groups. SBP, DBP, and MAP of the iron-injected group were lower than the control group (p=0.025, p=0.011, and p=0.008, respectively).CONCLUSION: Iron administration affects the expression of TTCCs but not the LTCCs, accompanied by decreasing of systolic and diastolic blood pressure.KEYWORDS: cardiomyopathy, iron overload, L-type calcium channel, T-type calcium channel.

AHNAK2 Is Associated with Poor Prognosis and Cell Migration in Lung Adenocarcinoma.

Background Lung adenocarcinoma (LUAD), as the main subtype of lung cancer, is one of the common causes of cancer-related deaths worldwide. The AHNAK family is correlated with cell structure and migration, cardiac calcium channel signaling, and tumor metastasis. Previous studies showed AHNAK2 could promote tumor progression and cell migration in melanoma and renal clear cell carcinoma. However, the role of AHNAK2 in LUAD remains unknown. Methods We examined the levels of AHNAK2 in pathological specimens and the database of Clinical Proteomic Tumor Analysis Consortium-Lung adenocarcinoma (CPTAC-LUAD), The Cancer Genome Atlas-Lung Adenocarcinoma (TCGA-LUAD), Gene Expression Omnibus dataset (GSE72094, GSE26939), and The Genotype-Tissue Expression (GTEx) of lung tissue samples. Univariate Cox regression, multivariate Cox regression, and Kaplan–Meier survival analysis were performed to reveal the relationship between AHNAK2 and prognosis. A nomogram was constructed to predict 2- or 3-year overall survival and validated via calibration curves, receiver operating characteristic (ROC) analysis, and decision curve analysis (DCA). Furthermore, Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were used to explore the functional role of AHNAK2 in lung adenocarcinoma. Finally, by transfecting siRNA, we examined the regulatory effect of AHNAK2 on cell migration. Results The expression of AHNAK2 was upregulated in tumor samples and correlated with poor prognosis in LUAD patients. Nomogram with AHNAK2 and clinical parameters showed a good prediction in overall survival (OS), especially the 2-year OS. In addition, functional analyses and wound healing assay suggested that AHNAK2 might be involved in the regulation of migration in LUAD. Conclusion In summary, our study showed that AHNAK2 might be a novel biomarker in LUAD and revealed the potential mechanism of AHNAK2 in LUAD progression which could provide new insights for target therapy.

158-OR: Calcium Channel Blockade Protects against Severe Hypoglycemia–Induced Fatal Cardiac Arrhythmias in Rats

It was hypothesized that in response to insulin-induced severe hypoglycemia, excess calcium influx into the heart causes fatal cardiac arrhythmias. To test if blocking the calcium channels would decrease fatal cardiac arrhythmias during severe hypoglycemia, L-type calcium channel blocker (Verapamil; 1 mg/kg, n = 25) or saline (n = 24) were infused into Sprague Dawley rats during a hyperinsulinemic (0.2 mU/kg/min) severe hypoglycemic (10-15 mg/dl) clamp for 3 hours with ECG. During severe hypoglycemia, verapamil completely prevented mortality compared to 21% mortality in controls (p < 0.05; Figure). Decreased mortality was associated with a 99% decrease in 2nd degree heart block (Figure) and prevention of 3rd degree heart block compared to saline (p < 0.05). Glucagon and epinephrine were similar between the groups suggesting verapamil does not affect hypoglycemic counterregulation. Consistent with the notion of calcium-mediated arrhythmias, separate experiments demonstrated that pharmacological blockade of ryanodine receptor-mediated calcium signaling also reduced heart block by 97% and prevented mortality due to hypoglycemia. In summary, blocking calcium channels protects against severe hypoglycemia-induced fatal cardiac arrhythmias. Blockade of cardiac calcium channels could be a potential approach to prevent arrhythmias in people with diabetes at risk for hypoglycemia. Disclosure C.M. Reno: None. Y. Huang: None. C.G. Christensen: None. M.B. Oxspring: None. J. Bayles: None. S.J. Fisher: None. Funding National Institutes of Health (5T32DK091317, R01NS070235); JDRF (3-APF-2017-407-A-N)

Fight or flight: The culprit is lurking in the neighbourhood

The fight-or-flight response is studied by all students of Physiology as a concerted bodily response to danger. Liu et al (2020) have now revealed its mechanism, after surveying the proteomic neighbourhood around the cardiac calcium channels in a study which is a tour-de-force of modern biological techniques.

191 WITHDRAWN:Â Validating the Significance of Ser1487 on α-1C Subunit in the Regulation of the Cardiac L-Type Calcium Channel During the “Fight or Flight” Response Using CRISPR/Cas9 Technology

191 WITHDRAWN:Â Validating the Significance of Ser1487 on α-1C Subunit in the Regulation of the Cardiac L-Type Calcium Channel During the “Fight or Flight” Response Using CRISPR/Cas9 Technology

The Reversal Effect of Sigma-1 Receptor (S1R) Agonist, SA4503, on Atrial Fibrillation After Depression and Its Underlying Mechanism.

AimSigma-1 receptors have been investigated and shown to play a protective role in both depression and cardiovascular disease. SA4503, known as a σ1 receptor agonist, regulates cardiac calcium and potassium channels in rat models of depression. However, it remains unknown whether SA4503 can alleviate myocardial inflammation or conduction junctions in the atrium after exposure to chronic mild stress.Methods and ResultsSprague-Dawley male rats received 28-day treatment with SA4503, simultaneously with chronic mild stress. Behavior measurements were assessed after the daily doses. Additionally, a multielectrode array assessment, electrophysiological study, immunohistochemistry analysis, histological analysis, and Western blot analysis were performed. Depression rats’ hearts showed abnormal electrical activity, including disordered excitation propagation and prolonged total activation time (TAT). In addition, atrial arrhythmias (AAs), induced by burst stimulation, showed higher incidence and longer duration in the depression group compared to the control group. These changes were related to reduced conduction junctions and enhanced spatial heterogeneity. Importantly, depressed rat hearts showed greater expression of inflammatory factors (TGF-α, IL-6, and TGF-β), more collagen distribution in the extracellular matrix, and lower expression of gap junction proteins (CX40 and CX43). Furthermore, SA4503 partially mitigated the above indices in the depression group (P < 0.01 for all groups).ConclusionThese findings show the effects of the σ1R agonist SA4503; it alleviates atrial myocardial inflammation and conduction junctions after chronic mild stress. SA4503 may be the promising pharmacological agent to treat depression-related AAs by increasing conduction function, improving the expression of connexin 40 and 43, and reducing cardiac myocardial inflammation.

Identification of a novel cAMP dependent protein kinase A phosphorylation site on the human cardiac calcium channel

The “Fight or Flight” response is elicited by extrinsic stress and is necessary in many species for survival. The response involves activation of the β-adrenergic signalling pathway. Surprisingly the mechanisms have remained unresolved. Calcium influx through the cardiac L-type Ca2+ channel (Cav1.2) is absolutely required. Here we identify the functionally relevant site for PKA phosphorylation on the human cardiac L-type Ca2+ channel pore forming α1 subunit using a novel approach. We used a cell free system where we could assess direct effects of PKA on human purified channel protein function reconstituted in proteoliposomes. In addition to assessing open probability of channel protein we used semi-quantitative fluorescent phosphoprotein detection and MS/MS mass spectrometry analysis to demonstrate the PKA specificity of the site. Robust increases in frequency of channel openings were recorded after phosphorylation of the long and short N terminal isoforms and the channel protein with C terminus truncated at aa1504. A protein kinase A anchoring protein (AKAP) was not required. We find the novel PKA phosphorylation site at Ser1458 is in close proximity to the Repeat IV S6 region and induces a conformational change in the channel protein that is necessary and sufficient for increased calcium influx through the channel.

Inhibition of CDK5 Alleviates the Cardiac Phenotypes in Timothy Syndrome.

SummaryL-type calcium channel CaV1.2 plays an essential role in cardiac function. The gain-of-function mutations in CaV1.2 have been reported to be associated with Timothy syndrome, a disease characterized by QT prolongation and syndactyly. Previously we demonstrated that roscovitine, a cyclin-dependent kinase (CDK) inhibitor, could rescue the phenotypes in induced pluripotent stem cell-derived cardiomyocytes from Timothy syndrome patients. However, exactly how roscovitine rescued the phenotypes remained unclear. Here we report a mechanism potentially underlying the therapeutic effects of roscovitine on Timothy syndrome cardiomyocytes. Our results using roscovitine analogs and CDK inhibitors and constructs demonstrated that roscovitine exhibits its therapeutic effects in part by inhibiting CDK5. The outcomes of this study allowed us to identify a molecular mechanism whereby CaV1.2 channels are regulated by CDK5. This study provides insights into the regulation of cardiac calcium channels and the development of future therapeutics for Timothy syndrome patients.

Abstract 111: Cdk5 is Associated in Cardiac Calcium Channelopathy

Cardiac calcium channels play important roles in hearts. Mutations in Ca V 1.2 channels are associated with cardiac arrhythmias including long QT syndrome type 8 (LQTS8). Using human induced pluripotent stem cells (iPSCs) to generate human cardiomyocytes from LQTS8 patients, we reported that the G406R mutation (LQTS8, Timothy syndrome) affected channel inactivation, action potentials and calcium handling in human cardiomyocytes. We found that roscovitine, a cyclin-dependent kinase (CDK) inhibitor, rescued the phenotypes in LQTS8 cardiomyocytes. However, how roscovitine restores the physiological functions in the patient cardiomyocytes remains unclear. Our recent results using roscovitine analogs and CDK inhibitors suggested that CDK5 is involved in the molecular bases of LQTS8. We found that dominant negative forms and shRNA of CDK5 alleviated the phenotypes of the LQTS8 cardiomyocytes and that the expressions of phosphorylated ERK, EGR1 and CDK5R1, a CDK5 activator, significantly increased in the patient cardiomyocytes. The results reveal that calcium overload due to affected Ca V 1.2 inactivation activates ERK/EGR1 pathway, resulting in increased expression of CDK5R1. Biochemical assays supported a direct binding and phosphorylation of Ca V 1.2 channels by CDK5. Overall, the results demonstrated that CDK5 regulates Ca V 1.2 channels and that CDK5 inhibition could be a new therapeutic for LQTS8. This study demonstrates the role of ERK/EGR1/CDK5 in pathogenesis of cardiac arrhythmia. The outcomes of this study provide new insights into Ca V 1.2 channel regulation.

Evidence for redox sensing by a human cardiac calcium channel.

Ion channels are critical to life and respond rapidly to stimuli to evoke physiological responses. Calcium influx into heart muscle occurs through the ion conducting α1C subunit (Cav1.2) of the L-type Ca2+ channel. Glutathionylation of Cav1.2 results in increased calcium influx and is evident in ischemic human heart. However controversy exists as to whether direct modification of Cav1.2 is responsible for altered function. We directly assessed the function of purified human Cav1.2 in proteoliposomes. Truncation of the C terminus and mutation of cysteines in the N terminal region and cytoplasmic loop III-IV linker did not alter the effects of thiol modifying agents on open probability of the channel. However mutation of cysteines in cytoplasmic loop I-II linker altered open probability and protein folding assessed by thermal shift assay. We find that C543 confers sensitivity of Cav1.2 to oxidative stress and is sufficient to modify channel function and posttranslational folding. Our data provide direct evidence for the calcium channel as a redox sensor that facilitates rapid physiological responses.

Regulation of Cardiac Calcium Channels in the Fight-or-Flight Response.

Intracellular calcium transients generated by activation of voltage-gated calcium (CaV) channels generate local signals, which initiate physiological processes such as secretion, synaptic transmission, and excitation-contraction coupling. Regulation of calcium entry through CaV channels is crucial for control of these physiological processes. In this article, I review experimental results that have emerged over several years showing that cardiac CaV1.2 channels form a local signaling complex, in which their proteolytically processed distal C-terminal domain, an A-Kinase Anchoring Protein, and cyclic AMP-dependent protein kinase (PKA) interact directly with the transmembrane core of the ion channel through the proximal C-terminal domain. This signaling complex is the substrate for β-adrenergic up-regulation of the CaV1.2 channel in the heart during the fight-or-flight response. Protein phosphorylation of two sites at the interface between the distal and proximal C-terminal domains contributes importantly to control of basal CaV1.2 channel activity, and phosphorylation of Ser1700 by PKA at that interface up-regulates CaV1.2 activity in response to β-adrenergic signaling. Thus, the intracellular C-terminal domain of CaV1.2 channels serves as a signaling platform, mediating beat-to-beat physiological regulation of channel activity and up-regulation by β-adrenergic signaling in the fight-or-flight response.

172 Junctophilin-2 interacts with the cardiac L-Type voltage-gated calcium channel

Background Excitation contraction (E-C) coupling in cardiac muscle is regulated by the L-type voltage-gated calcium channels (LTCC) within the t-tubules, and surface membrane, and the ryanodine receptors (RyR2) localised to the junctional sarcoplasmic reticulum (jSR). The juxtaposition of the t-tubules and jSR forms a microdomain termed a dyad. It is now widely accepted that junctophilin-2 (JP2) acts as a protein bridge to maintain the dyad geometry. JP2 is anchored in the SR, via its C-terminal transmembrane domain, and is thought to span the cytosol and interact with the plasma membrane thereby constraining the dyad architecture to provide the optimal proximal distance between the LTCCs and RyR2s to facilitate effective calcium induced calcium release for cardiac contraction. More recently, data has emerged to suggest that JP2 has an additional role, influencing E-C coupling through an interaction with RyR2. Furthermore, there is evidence for an association between JP2 and the LTCC in skeletal muscle. However, the region of the LTCC involved in binding to JP2 was not established nor was whether there is an interaction between JP2 and the LTCC in the heart. Methods We employed yeast-2-hybrid (Y2H) (Hybrigenics) experiments to investigate JP2 binding partners using human heart cDNA library. Domains of the LTCC were expressed as GST-fusion proteins and JP2 full-length and domains were purified from E.coli . Pull-down experiments were employed to investigate the interaction between the JP2 and the LTCC protein domains. Results Data from Y2H experiments identified the C-terminal region within the ion channel pore of LTCCs as a JP2 binding partner. Therefore, we designed a series of constructs encompassing the C-terminal domain of the Cav1.2 subunit and expressed them as GST-fusion proteins. Employing purified JP2 we showed a direct interaction with the C-terminal tail of Ca v 1.2. Furthermore, we determined that the N-terminal portion of JP2 mediates this interaction. We also investigated whether this interaction is Ca 2+ dependent since we have previously reported that JP2 has a cation binding domain. Our experiments revealed that the JP2-Ca v 1.2 interaction is independent of [Ca 2+ ]. Conclusion This study has provided novel data revealing that not only is there a direct interaction between the cardiac LTCC and JP2 but that the binding domains involve the C-terminal region of Ca v 1.2 and the N-terminal domain of JP2. Significantly, the Ca v 1.2 C-terminal domain binds calmodulin (CaM), both apoCaM and Ca 2+ CaM, regulating both calcium dependent inactivation (CDI) and facilitation (CDF) of the channel. Therefore, our future studies are directed at understanding the significance of JP2 binding, for example whether JP2 influences channel function (CDI/CDF) and/or whether a JP2-Ca v 1.2 is important for LTCC localisation to the dyad.

Propofol infusion syndrome in adults: a clinical update.

Propofol infusion syndrome is a rare but extremely dangerous complication of propofol administration. Certain risk factors for the development of propofol infusion syndrome are described, such as appropriate propofol doses and durations of administration, carbohydrate depletion, severe illness, and concomitant administration of catecholamines and glucocorticosteroids. The pathophysiology of this condition includes impairment of mitochondrial beta-oxidation of fatty acids, disruption of the electron transport chain, and blockage of beta-adrenoreceptors and cardiac calcium channels. The disease commonly presents as an otherwise unexplained high anion gap metabolic acidosis, rhabdomyolysis, hyperkalemia, acute kidney injury, elevated liver enzymes, and cardiac dysfunction. Management of overt propofol infusion syndrome requires immediate discontinuation of propofol infusion and supportive management, including hemodialysis, hemodynamic support, and extracorporeal membrane oxygenation in refractory cases. However, we must emphasize that given the high mortality of propofol infusion syndrome, the best management is prevention. Clinicians should consider alternative sedative regimes to prolonged propofol infusions and remain within recommended maximal dose limits.

Basal and β-adrenergic regulation of the cardiac calcium channel CaV1.2 requires phosphorylation of serine 1700.

L-type calcium (Ca(2+)) currents conducted by voltage-gated Ca(2+) channel CaV1.2 initiate excitation-contraction coupling in cardiomyocytes. Upon activation of β-adrenergic receptors, phosphorylation of CaV1.2 channels by cAMP-dependent protein kinase (PKA) increases channel activity, thereby allowing more Ca(2+) entry into the cell, which leads to more forceful contraction. In vitro reconstitution studies and in vivo proteomics analysis have revealed that Ser-1700 is a key site of phosphorylation mediating this effect, but the functional role of this amino acid residue in regulation in vivo has remained uncertain. Here we have studied the regulation of calcium current and cell contraction of cardiomyocytes in vitro and cardiac function and homeostasis in vivo in a mouse line expressing the mutation Ser-1700-Ala in the CaV1.2 channel. We found that preventing phosphorylation at this site decreased the basal L-type CaV1.2 current in both neonatal and adult cardiomyocytes. In addition, the incremental increase elicited by isoproterenol was abolished in neonatal cardiomyocytes and was substantially reduced in young adult myocytes. In contrast, cellular contractility was only moderately reduced compared with wild type, suggesting a greater reserve of contractile function and/or recruitment of compensatory mechanisms. Mutant mice develop cardiac hypertrophy by the age of 3-4 mo, and maximal stress-induced exercise tolerance is reduced, indicating impaired physiological regulation in the fight-or-flight response. Our results demonstrate that phosphorylation at Ser-1700 alone is essential to maintain basal Ca(2+) current and regulation by β-adrenergic activation. As a consequence, blocking PKA phosphorylation at this site impairs cardiovascular physiology in vivo, leading to reduced exercise capacity in the fight-or-flight response and development of cardiac hypertrophy.

Temporal expression of calcium channel subunits in satellite cells and bone marrow mesenchymal cells.

Bone marrow-derived mesenchymal stem cells (MSC) can be differentiated into myocytes, as well as adipocytes, chondrocytes, and osteocytes in culture. Calcium channels mediate excitation-contraction coupling and are essential for the function of muscle. However, little is known about the expression of calcium channel subunits and calcium handling in stem cells. We examined whether the expression of calcium channel subunits in MSC is similar to that of skeletal muscle satellite cells and if their levels of expression are modified after treatment with bone morphogenetic protein-4 (BMP4). We found that during myogenic differentiation, MSC first express the α2δ1 subunit and the cardiac channel subunit Cav1.2. In contrast to the α2δ1 subunit levels, the Cav1.2 subunit decreases rapidly with time. The skeletal channel subunit Cav1.1 is detected at day 3 but its expression increases considerably, resembling more closely the expression of the subunits in satellite cells. Treatment of MSC with BMP4 caused a significant increase in expression of Cav1.2, a delay in expression of Cav1.1, and a reduction in the duration of calcium transients when extracellular calcium was removed. Calcium currents and transients followed a pattern related to the expression of the cardiac (Cav1.2) or skeletal (Cav1.1) α1subunits. These results indicate that differentiation of untreated MSC resembles differentiation of skeletal muscle and that BMP4 reduces skeletal muscle calcium channel expression and promotes the expression of cardiac calcium channels during myogenic differentiation.

GW25-e4410 The Effects of Lysophosphatidylcholine on action potentials of cardiomyocyets and its mechanisms

To explore the effects of LPC on action potentials of cardiomyocytes and its mechanisms. Neonatal rat cardiomyocytes from 1 to 3-days Wistar rats were prepared, and the specific Human cardiac T-type calcium channel a1 subunits, Cav3.1 and Cav3.2, were stably expressed in HEK293 cells (HEK293-Cav3.1

PM376 Direct phosphorylation of the human cardiac L-type calcium channel alpha subunit by cAMP-dependent protein kinase alters function

PM376 Direct phosphorylation of the human cardiac L-type calcium channel alpha subunit by cAMP-dependent protein kinase alters function

Correction for Fu et al., Phosphorylation sites required for regulation of cardiac calcium channels in the fight-or-flight response

Correction for Fu et al., Phosphorylation sites required for regulation of cardiac calcium channels in the fight-or-flight response

Molecular mechanism of junctional membrane-targeting of cardiac and skeletal muscle L-type calcium channels.

横紋筋のL 型カルシウムチャネル（LTCC）は，筋収縮において電気信号をカルシウム信号に変換する重要な役割を担っている．LTCC と筋小胞体膜上に存在するリアノジン受容体（RyR）は，形質膜と筋小胞体膜が近接する結合膜構造で，機能的複合体を形成している．LTCC が結合膜構造に集積してクラスターを形成することは，筋の正常な興奮収縮連関に必要不可欠であるが，その詳細なメカニズムには不明な点が多く残されている．近年，骨格筋芽細胞株であるGLTを用いた研究により，骨格筋型LTCC の結合膜への局在化には，LTCC のポアを形成するCaV1.1 サブユニットのC末端配列が重要な役割を果たしていることが明らかになった．一方，成熟心筋細胞の培養が困難なため，心筋型LTCC の結合膜局在化の分子機構については，全く解析が進んでいなかった．我々はGLT 細胞を用いて，心筋LTCC の結合膜局在化機構を明らかにするための検討を行った．心筋LTCC のCaV1.2 サブユニットの各細胞内ドメインを，結合膜非局在性である神経型CaV2.1 サブユニットに置換した変異体を作製し，GLT 細胞に発現させた．その結果，近位C 末端の配列が結合膜への集積に必須であることが明らかになった．さらに，この部位に変異を導入すると，局在のみでなく，興奮収縮連関の効率も大きく低下することが分かった．また，LTCC の結合膜局在化に関係する分子として，ジャンクトフィリンに注目した検討も行った．C2C12 細胞のジャンクトフィリンをノックダウンすると，LTCC の結合膜への局在の阻害や，カルシウムトランジェントの減弱が認められた．また，共免疫沈降法によってLTCC のCaV1.1 サブユニットとジャンクトフィリンが結合していることが確認された．これらの結果は，ジャンクトフィリンがLTCC の正常な局在や機能に関与することを示唆している．

Phosphorylation sites required for regulation of cardiac calcium channels in the fight-or-flight response

L-type Ca(2+) currents conducted by CaV1.2 channels initiate excitation-contraction coupling in the heart. Their activity is increased by β-adrenergic/cAMP signaling via phosphorylation by PKA in the fight-or-flight response, but the sites of regulation are unknown. We describe the functional role of phosphorylation of Ser1700 and Thr1704-sites of phosphorylation by PKA and casein kinase II at the interface between the proximal and distal C-terminal regulatory domains. Mutation of both residues to Ala in STAA mice reduced basal L-type Ca(2+) currents, due to a small decrease in expression and a substantial decrease in functional activity. The increase in L-type Ca(2+) current caused by isoproterenol was markedly reduced at physiological levels of stimulation (3-10 nM). Maximal increases in calcium current at nearly saturating concentrations of isoproterenol (100 nM) were also significantly reduced, but the mutation effects were smaller, suggesting that alternative regulatory mechanisms are engaged at maximal levels of stimulation. The β-adrenergic increase in cell contraction was also diminished. STAA ventricular myocytes exhibited arrhythmic contractions in response to isoproterenol, and up to 20% of STAA cells failed to sustain contractions when stimulated at 1 Hz. STAA mice have reduced exercise capacity, and cardiac hypertrophy is evident at 3 mo. We conclude that phosphorylation of Ser1700 and Thr1704 is essential for regulation of basal activity of CaV1.2 channels and for up-regulation by β-adrenergic signaling at physiological levels of stimulation. Disruption of phosphorylation at those sites leads to impaired cardiac function in vivo, as indicated by reduced exercise capacity and cardiac hypertrophy.