Effects of postnatal maturation on postrest potentiation in isolated rabbit atria

ABSTRACT ABSTRACT. Ultrastructural changes in cardiac sarcoplasmic reticulum (SR) have been reported during postnatal development of the mammalian heart, but the functional significance of

these observations has not been well characterized. Calcium release from SR in intact myocardial preparations was determined by the contractile characteristics of postrest contractions.

Isometric tension and the maximum rate of tension development of the first contraction following intervals of electromechanical quiescence (rest) were related to steady-state tension and

maximum rate of tension development during contraction at constant frequency (1.0 Hz) in isolated left atrial strips from newborn (1-7 days), immature (14-21 days), and adult (more than 6

months) rabbits. The first postrest contraction was increased as a function of the rest interval rate of tension development, defined as postrest potentiation, in all three age groups and

reached a maximum value at rest intervals of more than 20 s. Tension developed by the first contraction following a 60-s rest interval was potentiated less in newborn and immature atria than

in adult atria at an extracellular calcium concentration ([Ca]e) of 2.5 mM, an age-related difference most marked in the immature. Ryanodine (5.0 × 10-9 M), a putative blocker of calcium

release from cardiac SR, abolished postrest potentiation providing evidence that calcium release from SR is the predominant determinant of the postrest contraction. Postrest tension in atria

from the immature rabbit heart was significantly increased both in absolute terms and relative to steady-state tension following stabilization under conditions which increase intracellular

[Ca] ([Ca]i, _i.e._ increasing [Ca]e, increasing tonicity, or decreasing extracellular sodium concentration ([Na]e). In contrast, postrest tension in atria from the adult rabbit heart

decreased relative to steady-state tension under conditions that increase [Ca]i. Rest potentiated contraction to a similar extent in both age groups (approximately 300% of steady-state) but

this maximum was obtained under markedly different ionic conditions. Maximum postrest potentiation occurred at 2.5 mM [Ca]e and 153.0 mM [Na]e in the adult atria whereas maximum potentiation

occurred at 5.0 mM [Ca]e and 87.0 mM [Na]e in immature atria. Results from experiments in which [Ca]e was increased during a 60-s rest interval suggest that the predominant effects of [Ca]e

on postrest potentiation are attributable to [Ca]e-dependent changes in [Ca]i as opposed to rest-dependent changes in transmembrane calcium conductance. These results lead us to conclude

that in rabbit atria: 1) contractile calcium released from the SR is demonstrated and therefore may potentially participate in excitation-contraction coupling during postnatal development;

2) the contribution of calcium released from the SR to contractile calcium during steady-state contraction may be less during early cardiac development; 3) the age-related differences in

postrest contraction can be abolished by manipulating ionic conditions to increase [Ca]i indicating that the immature SR requires higher [Ca]i for optimal calcium loading and/or “triggered”

release of calcium than does SR in the adult. SIMILAR CONTENT BEING VIEWED BY OTHERS SPONTANEOUS MYOGENIC FASCICULATION ASSOCIATED WITH THE LENGTHENING OF CARDIAC MUSCLE IN RESPONSE TO

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AFFILIATIONS * Departments of Pediatrics and Biochemistry, Vanderbilt University School of Medicine, Nashville, 37232, Tennessee Robert J Boucek Jr., Michael Citak, Thomas P Graham Jr. &

 Michael Artman Authors * Robert J Boucek Jr. View author publications You can also search for this author inPubMed Google Scholar * Michael Citak View author publications You can also

search for this author inPubMed Google Scholar * Thomas P Graham Jr. View author publications You can also search for this author inPubMed Google Scholar * Michael Artman View author

publications You can also search for this author inPubMed Google Scholar RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Boucek, R., Citak, M., Graham,

T. _et al._ Effects of Postnatal Maturation on Postrest Potentiation in Isolated Rabbit Atria. _Pediatr Res_ 22, 524–530 (1987). https://doi.org/10.1203/00006450-198711000-00011 Download

citation * Received: 24 April 1986 * Accepted: 22 June 1987 * Issue Date: 01 November 1987 * DOI: https://doi.org/10.1203/00006450-198711000-00011 SHARE THIS ARTICLE Anyone you share the

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