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1 Research Institute of Environmental Medicine, Nagoya University, Nagoya 464-01, Japan; 2 Department of Physiology, University of Leeds, Leeds LS2 9JT, United Kingdom; and 3 Department of Physiology, Iran University of Medical Sciences, Tehran, Iran
Effects of block
of the rapid delayed rectifier K+
current (IK,r)
by E-4031 on the electrical activity of small ball-like tissue preparations from different regions of the rabbit sinoatrial node were
measured. The effects of partial block of
IK,r by 0.1 µM E-4031 varied in different regions of the node. In tissue from the
center of the node spontaneous activity was generally abolished, whereas in tissue from the periphery spontaneous activity persisted, although the action potential was prolonged, the maximum diastolic potential was decreased, and the spontaneous activity slowed. After
partial block of
IK,r, the
electrical activity of peripheral tissue was more like that of central
tissue under normal conditions. One possible explanation of these
findings is that the density of
IK,r is greater
in the periphery of the node; this would explain the greater resistance
of peripheral tissue to
IK,r block and help explain why, under normal conditions, the maximum diastolic potential is more negative, the action potential is shorter, and pacemaking is faster in the periphery.
heart; cardiac; pacemaking
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