Jr. Berlin, SPATIOTEMPORAL CHANGES OF CA2-EVOKED CONTRACTIONS IN ATRIAL AND VENTRICULAR CELLS( DURING ELECTRICALLY), American journal of physiology. Heart and circulatory physiology, 38(3), 1995, pp. 1165-1170
Spatial and temporal changes of intracellular calcium ion concentratio
n ([Ca2+](i)) during stimulated contractions were observed by confocal
microscopy in rat ventricular and guinea pig atrial myocytes. Fluores
cence intensity profiles in flue 3-acetoxymethyl ester (fluo 3-AM)-loa
ded cells were collected from the entire cell, selected regions of the
cell, or along a single scanned line across the cell. In rat ventricu
lar myocytes, the increase of [Ca2+](i) after a single stimulus from f
ield electrodes occurred synchronously across the cell whether flue 3
fluorescence was monitored in a narrow region aligned with the long ax
is of the cell or in line-scan images of a single z-line across the ce
ll. However, during the onset of Ca2+ channel blockade by nifedipine (
5 mu M), electrical stimulation produced spatially nonuniform, focal i
ncreases of [Ca2+](i). In guinea pig atrial myocytes, stimulated incre
ases of [Ca2+](i) first appeared in focal regions at the cell peripher
y before spreading to the cell interior. Line-scan images showed the p
eripheral rise of [Ca2+](i) led that at the center of the cell by 34 /- 4 ms (mean +/- SE, n = 3). These data demonstrate that the t-tubula
r network ensures synchronous increases of [Ca2+](i) throughout the ce
ll during an action potential. In the absence of t tubules or when the
number of sarcolemmal Ca2+ channels opened by membrane depolarization
is greatly reduced, stimulated increases of [Ca2+](i) can be observed
to arise in focal regions of the cell.