| Abstrakt: |
At present ~20% of the Western population are over 65 years of age, and by 2050 this is predicted to increase to 25% [Cracknell, 2010]. The risk of atrial arrhythmias progressively increases in an age-dependent manner presumably due to structural and functional remodelling however the full details of this remains unknown. Our study has examined the effect of age on the protein expression of key calcium regulators and their mRNA expression across the atria. Male Wistar rats at the age of 6 months (young) and 24 months (old) (n=5) were sacrificed by an intraperitoneal anaesthetic overdose of pentobarbital. The right atrium (RA) and left atrium (LA) of each heart were assessed for changes in sarcoendoplasmic reticulum Ca2+ ATPase pump (SERCA2a), phospholamban (PLB), ryanodine receptors (RYR2), L-type calcium channels (Cav1.2) and sodium-calcium exchanger (NCX1). Western blot and immunocytochemistry were used to identify changes in protein expression and quantitative PCR changes in mRNA levels. Data are presented as mean±SEM, assessed by t-test or two-way ANOVA as appropriate (p<0.05). Ethical approval was given by the University of Hull. A comparison of atria in the young rat identified in the LA significantly higher protein levels of SERCA2a by 65.7±7.89% (p<0.001) and RYR2 60.7±8.09% (p<0.001), which correlated with elevated levels of mRNA in the LA for SERCA2a (92.2±7.8%; p=0.001) and RYR2 (27.5±4.8%; P=0.007). Ageing instigated a significant decline in all the investigated proteins within the RA; Cav1.2 fell by 46.4±6.2% (p=0.005), RYR2 by 25.7±4.11% (p=0.012), SERCA2a by 51.2±10.7% (p=0.009) and NCX1 by 57.1±3.63% (p=0.001), however there were no significant changes in their mRNA levels. In contrast the LA exhibited an increase of protein levels for Cav1.2 (52.5±2.5%, p=0.022) and NCX1 (27.5±2.9%, p=0.034), but in terms of mRNA levels only NCX1 significantly increased by 33.5±5.3% (p=0.005) with age. Data from immunocytochemistry reflected the data from western blot analysis. Comparing atria from the young animals, the ratio of SERCA2a to PLB monomer was significantly greater in the RA by 35.5±0.7% (p<0.001). Conversely considering each atrium and the effect of increased age, the ratio increased in the LA by 46±1.2% (p=0.001), but declined in the RA by 22±4.4% (p=0.01). In conclusion, existing inter-atrial heterogeneity of cellular calcium regulation increases in old age. The fall in RA proteins might be expected to reduce potential systolic function in old age whilst the LA changes, which have some parallels with changes seen in heart failure, may predispose to arrhythmias and calcium dysregulation. Combined these changes are a possible substrate for atrial fibrillation. [ABSTRACT FROM AUTHOR] |
