Regional ion channel gene expression heterogeneity and ventricular fibrillation dynamics in human hearts

RATIONALE: Structural differences between ventricular regions may not be the sole determinant of local ventricular fibrillation (VF) dynamics and molecular remodeling may play a role. OBJECTIVES: To define regional ion channel expression in myopathic hearts compared to normal hearts, and correlate expression to regional VF dynamics. METHODS AND RESULTS: High throughput real-time RT-PCR was used to quantify the expression patterns of 84 ion-channel, calcium cycling, connexin and related gene transcripts from sites in the LV, septum, and RV in 8 patients undergoing transplantation. An additional eight non-diseased donor human hearts served as controls. To relate local ion channel expression change to VF dynamics localized VF mapping was performed on the explanted myopathic hearts right adjacent to sampled regions. Compared to non-diseased ventricles, significant differences (p<0.05) were identified in the expression of 23 genes in the myopathic LV and 32 genes in the myopathic RV. Within the myopathic hearts significant regional (LV vs septum vs RV) expression differences were observed for 13 subunits: Nav1.1, Cx43, Ca3.1, Cavalpha2delta2, Cavbeta2, HCN2, Na/K ATPase-1, CASQ1, CASQ2, RYR2, Kir2.3, Kir3.4, SUR2 (p<0.05). In a subset of genes we demonstrated differences in protein expression between control and myopathic hearts, which were concordant with the mRNA expression profiles for these genes. Variability in the expression of Cx43, hERG, Na(+)/K(+) ATPase ss1 and Kir2.1 correlated to variability in local VF dynamics (p<0.001). To better understand the contribution of multiple ion channel changes on VF frequency, simulations of a human myocyte model were conducted. These simulations demonstrated the complex nature by which VF dynamics are regulated when multi-channel changes are occurring simultaneously, compared to known linear relationships. CONCLUSIONS: Ion channel expression profile in myopathic human hearts is significantly altered compared to normal hearts. Multi-channel ion changes influence VF dynamic in a complex manner not predicted by known single channel linear relationships

Autologous myoblast transplantation after myocardial infarction increases the inducibility of ventricular arrhythmias

Arrhythmogenesis after cell transplantation post-myocardial infarction. Four burning questions--and some answers. [Cardiovasc Res. 2006]International audienceBACKGROUND:Small scale clinical trials suggested the feasibility and the efficacy of autologous myoblast transplantation to improve ventricular function after myocardial infarction. However, these trials were hampered by unexpected episodes of life-threatening ventricular tachyarrhythmias (VT). We investigated cardiac electrical stability after myoblast transplantation to the myocardium.METHODS AND RESULTS:Seven days after coronary ligation, Wistar rats were randomized into 3 groups: a control group receiving no further treatment, a vehicle group injected with culture medium into the infarcted myocardium, and a myoblast group injected with autologous myoblasts. Holter monitoring did not discriminate the myoblast from the vehicle groups. Programmed Electrical Stimulation (PES) was performed to evaluate further a cardiac substrate for arrhythmia susceptibility. The occurrence of sustained VT during PES was similar in control and vehicle groups (5/17 and 4/19 rats, respectively; p=0.50). In contrast, 13/20 rats (65%) from the myoblast group showed at least one episode of sustained VT during PES (p<0.05 and p<0.005 versus control and vehicle groups). As a further control group, rats injected with autologous bone marrow mononuclear cells into the infarcted myocardium did not show increased susceptibility to PES.CONCLUSIONS:In an infarcted rat model, myoblast transplantation but not bone marrow mononuclear cells or myocardial injection per se induces electrical ventricular instability. Because ventricular arrhythmias are life-threatening disorders, we suggest that such preclinical evaluation should be conducted for any new source of cells to be injected into the myocardium

Computer simulations.

<p>Effect of protein level changes on average frequency. Starting with the left (A) or right (B) ventricular myopathic ionic model, parameters were changed to match expression levels in the other ventricle as specified in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0082179#pone-0082179-t002" target="_blank">Table 2</a>. Increases in frequency are red while decreases are blue, with brighter colors indicating more change from control. Each ring represents a simulation with each quarter circle representing a parameter change. If the parameter was altered for the simulation, it is colored coded according to the resultant frequency change, otherwise it is left as grey. Frequencies range from 4.71–4.99 Hz with a baseline frequency of 4.83 Hz for the LV and 4.76 Hz for the RV.</p

Comparison of K⁺ channel subunit expression levels between myopathic and normal RV's.

<p>Units for all values are 2^−ΔCt versus reference gene (×100), expressed as mean ± SEM. Only expression comparisons achieving p<0.05 are presented.</p

Significant (p<0.05) differences in gene expression levels between LV and RV samples within myopathic hearts.

<p>Differentially expressed genes in LV versus RV. Units for all expression values are 2^−ΔCt versus reference gene (×100). Only expressions comparisons achieving p<0.05 are depicted.</p

Comparison of Na⁺, Cl⁻ and Ca²⁺ channel subunits, Ca²⁺ handling proteins and exchanger expression levels between myopathic and normal LV's.

<p>Units for all values are 2^−ΔCt versus reference gene (×100), expressed as mean ± SEM. Only expression comparisons achieving p<0.05 are presented.</p

Comparison of K⁺ channel subunit expression levels between myopathic and normal LV's.

<p>Units for all values are 2^−ΔCt versus reference gene (×100), expressed as mean ± SEM. Only expression comparisons achieving p<0.05 are presented.</p

Comparison of protein expression in LV sample from control and cardiomyopathic patients.

<p>A: Top; representative SERCA2 and respective GAPDH stainings obtained in normal and cardiomyopathic LV samples. Bottom; Mean±SEM, *** P<0.001. B: Top; representative phospholamban (PLB) and respective GAPDH stainings obtained in normal and cardiomyopathic LV samples. Bottom; Mean±SEM, P = 0.051. C: Top; representative calsequestrin 2 (CSQ) and respective GAPDH stainings obtained in normal and cardiomyopathic LV samples. Bottom; Mean±SEM, * P<0.05. D: Top; representative Na/K-ATPase-α3 and respective GAPDH stainings obtained in normal and cardiomyopathic LV samples. Bottom; Mean±SEM, *** P<0.001. E: Top; representative Kir2.2 and respective GAPDH stainings obtained in normal and cardiomyopathic LV samples. Bottom; Mean±SEM, * P<0.05. F: Top; representative Kir2.3 and respective GAPDH stainings obtained in normal and cardiomyopathic LV samples. Bottom; Mean±SEM. n = 8 control LV samples, n = 6 cardiomyopathic LV samples.</p