Inotropic effects of ejection are myocardial properties
De Tombe, P.P.; Little, W.C.
American Journal of Physiology 266(3 Pt 2): H1202-H1213
1994
ISSN/ISBN: 0002-9513 PMID: 8160824 Document Number: 432817
Recent studies in isolated and in vivo canine hearts have suggested that the left ventricular end-systolic pressure (LVP-es) of ejecting beats is the net result of a balance between positive and negative effects of ejection. At present, it is unknown whether these ejection effects are merely a ventricular chamber property or represent a fundamental myocardial property. Accordingly, we examined the effects of ejection in eight isolated rat cardiac trabeculae at the sarcomere level. We approximated in situ sarcomere shortening patterns using an iterative computer loading system. Six isovolumic contractions were compared with four ejecting contractions. The superfusing solution contained either 0.7 mM Ca-2+ or 0.65 mM Sr-2+ plus 0.15 mM Ca-2+. With Ca-2+, simulated LVP-es ("LVP"es) of ejecting contractions was significantly lower than isovolumic "LVP"es (-5.3 +- 5.6%), whereas with Sr-2+, ejecting "LVP"es was significantly higher than isovolumic "LVP"es (+4.5 +- 7.5%). Contraction duration and time to end systole were markedly prolonged in ejecting vs. isovolumic contractions with either Ca-2+ or Sr-2+. As a consequence, comparison of simulated LVP between ejecting and isovolumic beats throughout the contraction, i.e., at the same simulated LVV and time, revealed only a positive effect of ejection with either Ca-2+ (+ 18.8 +- 5.5%) or Sr-2+ (+ 23.4 +- 9.3%). We conclude that both positive and negative effects of ejection are basic myocardial properties.