Altered action potential dynamics in electrically remodeled canine atria: evidence for altered intracellular Ca2+ handling.
BACKGROUND
Electrical instability following sustained rapid excitation has been attributed to altered ion channels. Alterations of Ca(2+) handling could also contribute to abnormal dynamics of action potential, favoring the initiation and perpetuation of arrhythmia.


RESULTS
Transmembrane action potentials and twitch force (TF) were recorded from normal (n=6) and remodeled (6-week atrial pacing at 400 beats/min, n=6) canine atria. When the cycle length (CL) was suddenly prolonged in normal atria, both TF and action potential duration (APD) increased on the first beat, and decreased subsequently. Opposite changes were observed with sudden CL shortening. These dynamics in both APD and TF were abolished by ryanodine, but augmented by cyclopiazonic acid, an inhibitor of the sarcoplasmic reticulum (SR) Ca(2+) pump. In remodeled atria (RA), dynamic changes in APD were also concordant with dynamic changes in TF. The transient increases in APD and TF were enhanced, and the transient decreases were reduced compared to normal atria. The maximal slopes of APD and TF restitution curves were flatter and the magnitude of alternans was reduced in RA. The protein expression of SR Ca(2+) ATPase and SR Ca(2+)-release channel in RA was significantly reduced.


CONCLUSIONS
Altered Ca(2+) handling may underlie abnormal APD dynamics in RA.
Hoshiyama
Koki
K
Department of Medicine, Cardiology Division, Keio University School of Medicine, Tokyo, Japan.
Hara
Motoki
M
Yasui
Kenji
K
Mitamura
Hideo
H
Ohsuzu
Fumitaka
F
Kodama
Itsuo
I
Ogawa
Satoshi
S
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004285:Dogs; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005786:Gene Expression Regulation / Q000235:genetics / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics / Q000502:physiology; D006325:Heart Atria / Q000166:cytology / Q000378:metabolism / Q000503:physiopathology*; D007211:Indoles / Q000494:pharmacology; D008297:Male; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000235:genetics / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000235:genetics / Q000378:metabolism; D013997:Time Factors
D004791:Enzyme Inhibitors; D007211:Indoles; D019837:Ryanodine Receptor Calcium Release Channel; D019831:Sodium-Calcium Exchanger; D012433:Ryanodine; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002118:Calcium; C000543:cyclopiazonic acid