© 1999 American Heart Association, Inc.
Rapid Communication |
Ca2+ Waves During Triggered Propagated Contractions in Intact Trabeculae
Determinants of the Velocity of Propagation
From the Department of Medicine (M.M., H.E.D.J.K.), University of Calgary, Calgary, Canada, and Department of Pharmacology (P.A.B.), Columbia College of Physicians and Surgeons, New York, NY.
Correspondence and reprint requests to Henk E.D.J. ter Keurs, MD, PhD, Department of Medicine, Health Science Centre, 3330 Hospital Dr NW, Calgary, Alberta, Canada T2N 4N1. E-mail terkeurs{at}ucalgary.ca
Abstract—During triggered
propagated contractions, Ca2+ waves travel along cardiac
trabeculae with a constant velocity (Vprop)
ranging from 0.34 to 5.47 mm/s. To explore the determinants of
Vprop, we studied (1) the relationship between
[Ca2+]i and Vprop and (2)
the effect of low concentrations of caffeine on Vprop.
Trabeculae were dissected from the right ventricle of rat
hearts. [Ca2+]i was measured using
electrophoretically injected fura-2 and an image-intensified CCD
camera. Force was measured using a silicon strain gauge, and sarcomere
length was measured using laser diffraction techniques. After induction
of reproducible Ca2+ waves by trains of electrical stimuli
(2.5 Hz) at 21.9±0.2°C, the number of stimuli or
[Ca2+]o was varied in 9
trabeculae. In 5 trabeculae, the effects of
caffeine (0.1 to 1.0 mmol/L) at [Ca2+]o
of 2.2±0.3 mmol/L were determined. All images were recorded
under stable conditions of wave propagation. The increment in
[Ca2+]i during the last electrically
stimulated transient (
CaT) and
[Ca2+]i just before onset of the
Ca2+ waves (CaD) were used to estimate the
Ca2+ loading of the sarcoplasmic reticulum (SR) and the
myoplasm, respectively. The ratio
(CaW/CaT) of the
[Ca2+]i increment during the waves
(CaW) to CaT was used to estimate the
probability of opening of the SR-Ca2+ release channel
during wave propagation. As a result of an increase of the number of
stimuli or [Ca2+]o, Vprop
increased in proportion to (1) CaT
(r=0.82); (2) CaD (r=0.88);
(3) CaW (r=0.85); and (4)
CaW/CaT (r=0.74). The
addition of caffeine (
0.3 mmol/L) increased Vprop
for any CaT and any CaW, revealing an
increased sensitivity of Vprop to CaT and
CaW. In contrast, caffeine had little effect on the
relationship between Vprop and CaD and no
effect on that between Vprop and
CaW/CaT. These results suggest that both
the cellular Ca2+ loading and open probability of the
SR-Ca2+ release channels determine the velocity of
propagation of Ca2+ waves.
Key Words: rat cardiac trabeculae • triggered propagated contraction • Ca2+ wave • caffeine
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