Economy of contraction of cardiomyocytes as influenced by different
positive inotropic interventions.
P[diaeresis]opping, S., S. Mruck, Y. Fischer, D. Kulsch, I. Ionescu,
H. Kammermeier, H. Rose.
Institute of Physiology, Medical Faculty, RWTH Aachen, Pauwelsstr.
30,
APStracts 2:0521H, 1995.
In the present study the effects of the novel cardiotonic agent EMD 57
033 on contraction and energetic demand of isolated, electrically
stimulated cardio myocytes are investigated and compared with the
effects of enhancement of extracellular calcium and of the -mimetic
isoproterenol. In a specially designed setup (1) parameters of
contractile behaviour and metabolic demand (oxygen consumption) of
isolated cardiac myocytes were measured. For a given enhancement of
contractile performance (cell shortening) the increase in energetic
demand (O2) after application of EMD 57 033 is markedly lower than
upon treatment with elevated extracellular Ca++-concentration or with
isoproterenol. This economization of positive inotropic effects is
proposed to be due to two factors:1) Stimulation-related ion-cycling
is only slightly enhanced with marked increase in contraction
amplitude after application of EMD 57 033. 2) Calcium sensitization
reflected in a leftward shift of the calcium concentration needed for
half-maximum force development can be interpreted to be mediated by
modulation of the crossbridge dynamics of the myofilaments, where
reduction of the switch-off rate of the crossbridges and prolongation
of their force-generating states are presumed to be involved. Lowered
pH (7.0) decreased economy of contraction. EMD restored contraction
amplitude and economy of contraction at lowered pH.
Received 2 August 1994; accepted in final form 9 November 1995.
APS Manuscript Number H691-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95