| Aims:To investigate the effects of docosahexaenoic acid (DHA) on atrial electricalremodeling and atrial fibrosis in atrial fibrillation rats and related mechanisms.Methods:1. Eighty Sprague-Dawley (SD) rats (250to300g) which sensitive to acetylcholine-calcium chloride mixture were randomly divided into the following groups: control(CTL), control treated with DHA (DHA), atrial fibrillation (AF) and atrial fibrillationtreated with DHA (DHA+AF)(n=20for each group). Rats in CTL and DHA groupswere injected with normal saline and rats in AF and DHA+AF groups were injectedwith acetylcholine (66μg/mL)-calcium chloride (50mg/mL) mixture via the trail veinat volume of0.1mL/100g once per day for three days. In the meanwhile,electrocardiograms were recorded. From the fourth day, rats in CTL group wereinjected with normal saline and rats in DHA group were injected with DHA(10mg/mL) and normal saline, and rats in AF group were injected with normal salineand acetylcholine (66μg/mL)-calcium chloride (50mg/mL) mixture, rats in DHA+AFgroup were injected with DHA (10mg/mL) and acetylcholine (66μg/mL)-calciumchloride (50mg/mL) mixture via the trail vein at volume of0.1mL/100g once per dayfor fourteen days. Electrocardiograms were recorded on the4th,10thand17thday ofthe experiment.2. The effects of DHA on the duration of atrial fibrillation in atrial fibrillation ratsinduced by acetylcholine-calcium chloride mixture were observed.3. The effects of DHA on atrial electrical remodeling were observed by using doublestimulation method to detect the atrial effective refractory period (ERP), andwhole-cell patch-clamp technique to record the atrial myocyte action potential duration (APD) and TWIK-related acid-sensitive K+channels-1(TASK-1) currents.4. The expressions of TASK-1mRNA and protein in atrial tissue were detected byQuantitative real-time PCR method and Western blot method.5. The effects of DHA on atrial collagen fiber hyperplasia were detected by Massonstaining.6. The collagen type Ⅰ mRNA expression in atrial tissue was detected byQuantitative real-time PCR; the extracellular signal-regulated kinase1/2(ERK1/2),phosphorylated extracellular signal-regulated kinase1/2(p-ERK1/2) and collagentype Ⅰ protein expressions in atrial tissue were detected by Western blot method.Results:1. Effects of DHA on the duration of atrial fibrillationThe duration of atrial fibrillation induced by acetylcholine-calcium chloridemixture was gradually extended with the extension of the experimental time, andDHA could shorten the duration of atrial fibrillation.2. Effects of DHA on atrial effective refractory period and atrial myocyte actionpotential durationCompared with control group, the time of atrial ERP was significantly shorten inAF group (From79.5±5.8ms to57.2±6.1ms, P <0.05), and was significantlyprolonged in DHA group (From79.5±5.8ms to99.5±8.6ms, P <0.05) and DHA+AFgroup (From79.5±5.8ms to90.2±7.4ms, P <0.05). Compared with AF group, thetime of atrial ERP was significantly prolonged in DHA+AF group (P <0.05).Compared with control group, the time of atrial myocyte action potentialduration at50%repolarization (APD50) and action potential duration at90%repolarization (APD90) were significantly shorten in AF group (P <0.05), and weresignificantly prolonged in DHA group (P <0.05) and DHA+AF group (P <0.05).Compared with AF group, the time of atrial myocyte APD50and APD90weresignificantly prolonged in DHA+AF group (P <0.05). 3. Effects of DHA on atrial TASK-1current and TASK-1mRNA and proteinexpressionsCompared with control group, the TASK-1current density in atrial myocyte wassignificantly increased in AF group (at+30mV, from1.65±0.14pA/pF to2.36±0.17pA/pF, P <0.05) and DHA+AF group (at+30mV, from1.65±0.14pA/pF to1.90±0.12pA/pF, P <0.05), and was significantly reduced in DHA group (at+30mV,from1.65±0.14pA/pF to1.26±0.11pA/pF, P <0.05). Compared with AF group, theTASK-1current density in atrial myocyte was significantly reduced in DHA+AFgroup (P <0.05).Compared with control group, expression of TASK-1mRNA in atrial tissue wassignificantly increased in AF group (P <0.05) and DHA+AF group (P <0.05), andwas significantly reduced in DHA group (P <0.05). Compared with AF group,expression of TASK-1mRNA in atrial tissue was significantly reduced in DHA+AFgroup (P <0.05).Compared with control group, expression of TASK-1protein in atrial tissue wassignificantly increased in AF group (P <0.05) and DHA+AF group (P <0.05), andwas significantly reduced in DHA group (P <0.05). Compared with AF group,expression of TASK-1protein in atrial tissue was significantly reduced in DHA+AFgroup (P <0.05).4. Effects of DHA on atrial fibrosisIn control group and DHA group, the atrial was normal and showed smallamounts of interstitial fibrous tissue. While, in AF group, there was extensiveinterstitial fibrosis in the atrial. In DHA+AF group, fibrosis was strongly attenuated toa level significantly different from AF group.5. Effects of DHA on ERK1/2expression and phosphorylationThe expression of total ERK1/2protein had no significant differences in eachgroups, while the expression of p-ERK1/2protein had changed, and thep-ERK1/2/ERK1/2protein ratio had changed. Compared with control group, thep-ERK1/2/ERK1/2protein ratio in atrial tissue was significantly increased in AFgroup (P <0.05), and was significantly decreased in DHA group (P <0.05). Compared with AF group, the p-ERK1/2/ERK1/2protein ratio in atrial tissue wassignificantly decreased in DHA+AF group (P <0.05).6. Effects of DHA on expressions of collagen type Ⅰ mRNA and proteinCompared with control group, the expressions of collagen type Ⅰ mRNA andprotein in atrial tissue were significantly increased in AF group (P <0.05) andDHA+AF group (P <0.05). Compared with AF group, the expressions of collagentype Ⅰ mRNA and protein in atrial tissue were significantly reduced in DHA+AFgroup (P <0.05).Conslusions:1. DHA can prolong the atrial myocyte APD and atrial ERP and improve atrialelectrical remodeling in atrial fibrillation rats. The mechanism of the effect may berelated to down-regulation of TASK-1mRNA and protein expressions in atrial tissue.2. DHA can improve atrial fibrosis in atrial fibrillation rats. The mechanism of theeffect may be related to down-regulation of collagen type Ⅰ mRNA and proteinexpressions by inhibiting ERK1/2activation in atrial tissue. |
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