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Genesis and Regulation of the Heart Automaticity

Institute of Functional Genomics, Department of Physiology, Centre National de la Recherche Scientifique UMR5203, Institut National de la Santé et de la Recherche Médicale U661, University of Montpellier I and II, Montpellier, France

The heart automaticity is a fundamental physiological function in higher organisms. The spontaneous activity is initiated by specialized populations of cardiac cells generating periodical electrical oscillations. The exact cascade of steps initiating the pacemaker cycle in automatic cells has not yet been entirely elucidated. Nevertheless, ion channels and intracellular Ca²⁺ signaling are necessary for the proper setting of the pacemaker mechanism. Here, we review the current knowledge on the cellular mechanisms underlying the generation and regulation of cardiac automaticity. We discuss evidence on the functional role of different families of ion channels in cardiac pacemaking and review recent results obtained on genetically engineered mouse strains displaying dysfunction in heart automaticity. Beside ion channels, intracellular Ca²⁺ release has been indicated as an important mechanism for promoting automaticity at rest as well as for acceleration of the heart rate under sympathetic nerve input. The potential links between the activity of ion channels and Ca²⁺ release will be discussed with the aim to propose an integrated framework of the mechanism of automaticity.