Objective To investigate the molecular mechanism and characteristics of atrial electrical remodeling parameters in atrial fibrillation(AF) model using monophasic action potential(MAP).Methods Seventeen mongrel dogs were randomly divided into two groups.Eleven dogs were subjected to rapid right atrial pacing(350-430 beats/min) for 8 weeks(AF group),and another 6 sham-operated dogs served as controls.Before and after 8 weeks pacing,electrophysiological examinations were performed to calculate atrial effective refractory period(AERP).The MAP amplitude(MAPA),duration(MAPD),90% repolarization duration(MAPD90),50% repolarization(MAPD50) and MAPD90-50 were measured according to MAP recordings.The content of myocardial calcium was assayed by spectrocomparator in atrial myocardium from all dogs.The messenger ribonucleic acid(mRNA) level of sarcoplasmic reticular(SR) Ca2+-ATPase and L-type calcium channel were measured by reverse transcription-polymerase chain reaction(RT-PCR) and normalized to the mRNA level of β-actin.Results Each phase of MAP was easily discerned in control dogs.Morphology of MAP was significantly changed in AF group.Compared with control group,MAPA of AF group had a tendency to decrease.MAPD,MAPD90,MAPD50 and MAPD90-50 were shortened by 16.20%,19.65%,13.59% and 31.25%,respectively.MAPD,MAPD90 and MAPD90-50 were negatively correlated to the content of calcium in right atrial myocardium.MAPD90-50 was positively correlated to the mRNA level of L-type calcium channel.All parameters had no relation to mRNA level of SR Ca2+-ATPase.Conclusion MAP provides a reliable method to investigate atrial fibrillation electrical remodeling.Changes in L-type calcium channel and SR Ca2+-ATPase may be one of the mechanism of atrial electrical remodeling.