RT-31
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Mechanisms underlying the initiation of normal and abnormal automaticity in Purkinje fibers
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Mario Vassalle, Daniel E.Berg.
Department of Physiology and Pharmacology, State University of New York, Health Science Center, New York, USA
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Introduction
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In vitro, at physiological [K+]o (4-5 mM) stoppage of drive
of Purkinje fibers is followed by a diastolic depolarization that reaches a steady resting potential.
The resting fibers become spontaneously active only when [K+]o is decreased to ~2.7 mM. If [K+]o
is decreased further, Purkinje fibers depolarize at the plateau and the abnormal spontaneous
discharge consists of slow responses.
These findings raise several questions: 1) what are the mechanisms that permit the attainment of
the threshold and the initiation of spontaneous discharge when [K+]o is lowered?; 2) are the same
mechanisms important for the maintenance of spontaneous discharge? 3) what is responsible for
depolarization at the plateau in low [K+]o?; 4) what are the mechanisms allowing initiation of
spontaneous slow responses?; 5) are the mechanisms initiating spontaneous discharge at polarized
and depolarized levels different?; and 6) at polarized levels, can these mechanisms attain the
threshold either through diastolic depolarization or phase 3 repolarization (recovery from low[K+]o)?
We review here the answers obtained in our laboratory.
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