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The Scientific World Journal
Volume 2013 (2013), Article ID 507872, 10 pages
Research Article

Calcium Transient and Sodium-Calcium Exchange Current in Human versus Rabbit Sinoatrial Node Pacemaker Cells

1Department of Anatomy, Embryology and Physiology, Academic Medical Center, University of Amsterdam, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands
2Laboratory of Clinical Chemistry and Hematology, Jeroen Bosch Hospital, Henri Dunantstraat 1, 5223 GZ 's-Hertogenbosch, The Netherlands

Received 11 January 2013; Accepted 7 February 2013

Academic Editors: Y. Du and Y. Wang

Copyright © 2013 Arie O. Verkerk et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


There is an ongoing debate on the mechanism underlying the pacemaker activity of sinoatrial node (SAN) cells, focusing on the relative importance of the “membrane clock” and the “ clock” in the generation of the small net membrane current that depolarizes the cell towards the action potential threshold. Specifically, the debate centers around the question whether the membrane clock-driven hyperpolarization-activated current, , which is also known as the “funny current” or “pacemaker current,” or the Ca2+ clock-driven sodium-calcium exchange current, , is the main contributor to diastolic depolarization. In our contribution to this journal’s “Special Issue on Cardiac Electrophysiology,” we present a numerical reconstruction of and in isolated rabbit and human SAN pacemaker cells based on experimental data on action potentials, , and intracellular calcium concentration ( ) that we have acquired from these cells. The human SAN pacemaker cells have a smaller , a weaker transient, and a smaller than the rabbit cells. However, when compared to the diastolic net membrane current, is of similar size in human and rabbit SAN pacemaker cells, whereas is smaller in human than in rabbit cells.