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The role of the calcium and the voltage clocks in sinoatrial node dysfunction

Title
 The role of the calcium and the voltage clocks in sinoatrial node dysfunction 
Authors
 Boyoung Joung ; Peng-Sheng Chen ; Shien-Fong Lin 
Issue Date
2011
Journal Title
 Yonsei Medical Journal 
ISSN
 0513-5796 
Citation
 Yonsei Medical Journal, Vol.52(2) : 211~219, 2011 
Abstract
Recent evidence indicates that the voltage clock (cyclic activation and deactivation of membrane ion channels) and Ca(2+) clocks (rhythmic spontaneous sarcoplasmic reticulum Ca(2+) release) jointly regulate sinoatrial node (SAN) automaticity. However, the relative importance of the voltage clock and Ca(2+) clock for pacemaking was not revealed in sick sinus syndrome. Previously, we mapped the intracellular calcium (Ca(i)) and membrane potentials of the normal intact SAN simultaneously using optical mapping in Langendorff-perfused canine right atrium. We demonstrated that the sinus rate increased and the leading pacemaker shifted to the superior SAN with robust late diastolic Ca(i) elevation (LDCAE) during β-adrenergic stimulation. We also showed that the LDCAE was caused by spontaneous diastolic sarcoplasmic reticulum (SR) Ca(2+) release and was closely related to heart rate changes. In contrast, in pacing induced canine atrial fibrillation and SAN dysfunction models, Ca(2+) clock of SAN was unresponsiveness to β-adrenergic stimulation and caffeine. Ryanodine receptor 2 (RyR2) in SAN was down-regulated. Using the prolonged low dose isoproterenol together with funny current block, we produced a tachybradycardia model. In this model, chronically elevated sympathetic tone results in abnormal pacemaking hierarchy in the right atrium, including suppression of the superior SAN and enhanced pacemaking from ectopic sites. Finally, if the LDCAE was too small to trigger an action potential, then it induced only delayed afterdepolarization (DAD)-like diastolic depolarization (DD). The failure of DAD-like DD to consistently trigger a sinus beat is a novel mechanism of atrial arrhythmogenesis. We conclude that dysfunction of both the Ca(2+) clock and the voltage clock are important in sick sinus syndrome.
URI
http://ir.ymlib.yonsei.ac.kr/handle/22282913/92989
DOI
10.3349/ymj.2011.52.2.211
Appears in Collections:
1. 연구논문 > 1. College of Medicine > Dept. of Internal Medicine
Yonsei Authors
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