Effects of cardiac remodeling on atrial arrhythmogenesis in aged rabbit left atrium / 中国病理生理杂志

ABSTRACT

AIM: To investigate the effects of myocardial remodeling of aged left atrium (LA) on atrial ar-rhythmogenesis in rabbits .METHODS:The male New Zealand rabbits were divided into young LA and aged LA groups . By observing the changes of monophasic action potential ( MAP) and burst-pacing in LA of the rabbits in vivo, the main cardioelectrophysiological parameters such as resting membrane potential ( RMP) , action potential amplitude ( APA) , ma-ximum rise veloctiy of action potential (dv/dtmax), plateau potential and action potential duration at 30%, 50%and 90%( APD30 , APD50 and APD90 ) , as well as the inducibility and duration of atrial arrhythmias were recorded .L-type calcium current (ICa,L) was analyzed via whole-cell patch-clamp technique in enzymatically dissociated single rabbit LA myocytes . The myocardial collagen content was quantified after Masson staining , and the ultrastructure of the LA cells was observed under scanning electron microscope .The expression of Cav 1.2 in LA tissue of the 2 groups was detected by Western blot . RESULTS:Compared with young LA group , dv/dtmax and plateau potential were significantly decreased , APD30 and APD50 were shortened, and APD90 was notably prolongated in aged LA group (P<0.01).The inducibility or duration of atrial arrhythmias was severely increased or prolongated in aged LA group (P<0.01).With voltage clamp model, the den-sity of ICa,L in aged LA group was significantly decreased , and current-voltage curve was notably moved upward compared with young LA group.When the clamp potential was +20 mV, the density of ICa,L was notably modified from (11.72 ± 1.39) pA/pF in young LA group to (6.08 ±0.98) pA/pF in aged LA group ( P<0.01).Compared with young LA group, the protein level of collagen was significantly increased (P<0.01), and the arrange of atrial myocytes was irregular in LA of rabbits in aged LA group .The atrial myocytes of the LA wall in aged LA group exhibited abnormal ultrastructural alterations , such as karyopyknosis , irregular and swelling mitochondria with the presence of vacuoles , and mild and severe sarcomere degeneration .Compared with those in LA tissues of young rabbits , the expression levels of Cav 1.2 in the LA tis-sues of aged rabbits were severely reduced (P<0.01), and had a significant positive correlation with the reduction of ICa,L (r=0.83, P<0.01).CONCLUSION:The pathophysiological characteristics of aged LA are significantly altered , and might contribute to vulnerability and susceptibility of occurrence of atrial fibillation in aged rabbits .The mechanisms might completely attribute to the notable reduction of ICa,L , abnormal alterations of ultrastructures and obvious decrease in the ex-pression of Cav1.2 in the aged LA of aged rabbits .