OBJECTIVETo investigate rapid atrial pacing (RAP) induced atrial ultrastructural changes and mRNA and protein expression changes of L-type calcium channel subunits and potassium channel Kv4.3 in a rabbit model.

METHODSThirty-six rabbits were electrically paced at a frequency of 600 beats/min for durations ranging from 0 - 48 h via bipolar endocardial leads through surgical techniques. Ultrastructural changes of the atrium were observed through a transmission electron microscope (TEM), L-type calcium channel subunits and potassium channel Kv4.3 expressions at mRNA and protein levels were analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot.

RESULTSAtrial ultrastructure changes characterized by mitochondrial vacuolization, myofilament lysis, and glycogen accumulation were detected obvious at 3 h post pacing. Down-regulated mRNA expression of Ca(2+) channel beta1 and alpha1 subunits was observed 6 h post pacing, Kv4.3 mRNA down-regulation occurred 24 h post pacing, auxiliary subunit alpha2 was not affected by pacing. Protein expression of alpha1c subunit and potassium channel Kv4.3 paralleled their mRNA expression changes.

CONCLUSIONRAP induced ultrastructural changes of the atrium and down-regulated mRNA and protein expressions of L-type calcium channel subunits and potassium channel Kv4.3 occurred thereafter in response to intracellular calcium overload induced by RAP.