Characterization of ca2+ release channels in fetal and adult rat
hearts.
Ramesh, Venkat, Mitchell J. Kresch, Arnold M. Katz, and Do Han Kim.
Division of Cardiology, Department of Medicine and Division of
Neonatalogy, Department of Pediatrics, University of Connecticut
Health Center, Farmington, CT, USA, 06030-1305, and Kwangju Institute
of Science and Technology (K-JIST), Kwangju, Korea
APStracts 2:0079H, 1995.
The goal of this study was to characterize the Ca2+ release channel in
whole homogenates of left (LV) and right ventricles (RV) of fetal (22
days in gestation) and adult Sprague-Dawley rat hearts using
[3H]ryanodine binding and 45Ca2+ fluxes. Although many features of
the Ca2+ release channels were similar in fetal and adult hearts,
biochemical assays revealed quantitative differences. Similar
properties include 1) Ca2+-sensitive cooperative ryanodine binding to
Ca2+ release channel, measured as Ca2+ concentration for half-maximal
activation (fetal LV: 0.13 +/- 0.02 [mu]M; adult LV: 0.15 +/- 0.02
[mu]M) and Hill coefficient (fetal LV: 2.5 +/- 0.9; adult LV: 2.7 +/-
0.5), and 2) caffeine-sensitive ryanodine binding, measured as the %
increase in ryanodine binding induced by caffeine (fetal LV: 148.8
+/- 16.9 % vs adult LV: 171.4 +/- 34.9 %). The distinguishing
property was the lower Ca2+ release channel density in the fetal
heart (LV: 0.22 +/- 0.03 pmol/mg protein), compared to adult heart
(LV: 0.59 +/- 0.04 pmol/mg protein; p<0.05), as determined by [3
H]ryanodine binding. The lower density of Ca2+ release channel is
supported by the finding that there is very low ryanodine-sensitive
oxalate-supported 45Ca2+ uptake in the fetal heart. The tested
characteristics of the Ca2+ release channel were similar between left
and right ventricles in both fetal and adult rat hearts. Our results
indicate that expression of Ca2+ release channels in sarcoplasmic
reticulum (SR) increases during postnatal growth in the rat heart.
This is consistent with previous physiological reports that Ca2+
available for excitation-contraction coupling in the fetal heart is
derived mainly from trans-sarcolemmal Ca2+ influx.
Received 19 September 1994; accepted in final form 3 March 1995.
APS Manuscript Number H847-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 21 March 1995.