Cilostazol ameliorates atrial ionic remodeling in long-term rapid atrial pacing dogs

Abstract

Objective: Ionic remodeling has a close correlation with the occurrence of atrial fibrillation (AF). Atrial tachypacing remodeling is associated with characteristic ionic remodeling. The purpose of this study was to assess the efficacy of cilostazol, an oral phosphodiesterase 3 inhibitor, for preventing atrial ionic remodeling in long-term rapid atrial pacing (RAP) dogs.

Methods: We use the methods of patch-clamp and molecular biology to investigate the effect of cilostazol on ion channel and channel gene expression in long-term RAP dogs. Twenty-one dogs were randomly assigned to sham, control paced, and paced+cilostazol (5 mg/kg/d, cilo) groups, with 7 dogs in each group. The sham group was instrumented with a pacemaker but without pacing. RAP at 500 beats/min was maintained for 2 weeks in the paced and cilo groups. During the pacing, cilostazol was given orally in the cilo group. Whole-cell patch-clamp technique was used to record atrial L-type Ca2+ (ICaL) and fast sodium channel (INa) ionic currents. Western blot and RT-PCR were applied to estimate the gene expression of the ICaLα) 1C (Cav1.2) and INav1.5α) Nav1.5α) subunits. Statistical analysis was performed using SPSS 13.0.

Results: The density of ICaL and INa currents (pA/pF) was significantly reduced in the paced group (ICaL: -6.55±1.42 vs. -4.46±0.59 pA/pF; INa: -48.24±10.54 vs. -30.48±5.20 pA/pF, p<0.01). The paced+cilo group could not increase the density of ICaL currents (ICaL: -4.37±1.25 pA/pF, p>0.05), while the INa currents were recovered (-44.54±12.65 pA/pF, p<0.01) compared with the paced group. The mRNA and protein expression levels of Cav1.2 and Nav1.5α were apparently down-regulated in the paced group (p<0.01), but after cilostazol treatment, both of these subunits were up-regulated significantly (p<0.01).

Conclusion: Cilostazol may have protective effects on RAP-induced atrial ionic remodeling.

Figure 1

a-f. I-V curves of I_CaL and the relative gene expression levels of Cav1.2 in three groups. (a) I-V curves of I_CaL obtained from dogs of various groups. TP (test potential). (b) Columns and error bars indicate mean±SEM, respectively. (c) Representative Cav1.2 RT-PCR results. (d) Columns and error bars indicate mean±SEM of Cav1.2 RT-PCR results. (e) Representative the Cav1.2 western blot results. (f) Columns and error bars indicate mean±SEM Cav1.2 western blot results. The relative gene expression levels of Cav1.2 were decreased by RAP. Cilostazol markedly upregulated the gene expression levels of Cav1.2. Data are presented as relative gene expression (n=6). *P<0.01 vs. corresponding value in sham group; ΔP<0.01 vs. corresponding value in paced group

Figure 2

a-f. I-V curves of I_Na and the relative gene expression levels of Nav1.5a in the three groups. (a) I-V curves of I_Na obtained from dogs of various groups. TP (test potential). (b) Columns and error bars indicate mean±SEM, respectively. (c) Representative the Nav1.5a RT-PCR results. (d) Columns and error bars indicate mean±SEM. (e) Representative Nav1.5a western blot results. (f) Columns and error bars indicate mean±SEM Nav1.5a western blot results. The relative gene expression levels of Nav1.5a were decreased by RAP. Cilostazol markedly upregulated the gene expression levels of Nav1.5a. Data are presented as relative gene expression (n=6). *P<0.01 vs. corresponding value in sham group, ΔP<0.01 vs. corresponding value in paced group

Figure 3

a, b. Active curves of I_CaL and I_Na in the three groups. (a) Active curves of I_CaL obtained from dogs of various groups. TP (test potential). (b) Active curves of I_Na obtained from dogs of various groups