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Ca(2+) transients and Ca(2+) waves in purkinje cells : role in action potential initiation.

Abstract：

:Purkinje cells contain sarcoplasmic reticulum (SR) directly under the surface membrane, are devoid of t-tubuli, and are packed with myofibrils surrounded by central SR. Several studies have reported that electrical excitation induces a biphasic Ca(2+) transient in Purkinje fiber bundles. We determined the nature of the biphasic Ca(2+) transient in aggregates of Purkinje cells. Aggregates (n=12) were dispersed from the subendocardial Purkinje fiber network of normal canine left ventricle, loaded with Fluo-3/AM, and studied in normal Tyrode's solution (24 degrees C). Membrane action potentials were recorded with fine-tipped microelectrodes, and spatial and temporal changes in [Ca(2+)](i) were obtained from fluorescent images with an epifluorescent microscope (x20; Nikon). Electrical stimulation elicited an action potential as well as a sudden increase in fluorescence (L(0)) compared with resting levels. This was followed by a further increase in fluorescence (L(1)) along the edges of the cells. Fluorescence then progressed toward the Purkinje cell core (velocity of propagation 180 to 313 microm/s). In 62% of the aggregates, initial fluorescent changes of L(0) were followed by focally arising Ca(2+) waves (L(2)), which propagated at 158+/-14 microm/s (n=13). Spontaneous Ca(2+) waves (L(2)*) propagated like L(2) (164+/-10 microm/s) occurred between stimuli and caused slow membrane depolarization; 28% of L(2)* elicited action potentials. Both spontaneous Ca(2+) wave propagation and resulting membrane depolarization were thapsigargin sensitive. Early afterdepolarizations were not accompanied by Ca(2+) waves. Action potentials in Purkinje aggregates induced a rapid rise of Ca(2+) through I(CaL) and release from a subsarcolemmal compartment (L(0)). Ca(2+) release during L(0) either induced further Ca(2+) release, which propagated toward the cell core (L(1)), or initiated Ca(2+) release from small regions and caused L(2) Ca(2+) waves, which propagated throughout the aggregate. Spontaneous Ca(2+) waves (L(2)*) induce action potentials.

journal_name

Circ Res

journal_title

Circulation research

authors

Boyden PA,Pu J,Pinto J,Keurs HE

doi

10.1161/01.res.86.4.448

subject

Has Abstract

pub_date

2000-03-03 00:00:00

pages

448-55

issue

eissn

0009-7330

issn

1524-4571

journal_volume

pub_type

杂志文章

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Ca(2+) transients and Ca(2+) waves in purkinje cells : role in action potential initiation.