ORIGINAL CONTRIBUTION Basic Res Cardiol 95: 378 – 384 (2000) © Steinkopff Verlag 2000 Thierry Joseph Catherine Coirault Yves Lecarpentier Species-dependent changes in mechano-energetics of isolated cardiac muscle during hypoxia Abstract The present study investigates the mechanical and energetic changes induced by hypoxia in isolated cardiac muscles of different species characterized by different myosin isoforms. Classic mechanical parameters of contraction and ener- getic parameters derived from the tension-velocity relationship were studied in rat and guinea pig left ventricular papillary muscles and in frog ventricular strips before and after 15 min hypoxia (n = 8 in each group). The isomyosin pattern is predomi- nantly V1 with high ATPase activity in rat and V3 with low ATPase activity in guinea pig and frog heart ventricles. At baseline, cardiac mechanical performance was greater in rat than in guinea pig and frog muscle, but the economy of tension gen- eration did not differ significantly between the three species. Hypoxia significantly decreased myocardial mechanical performance in all three groups. Mechanical impairment was more marked in rat than in the other two species and was inter- mediate in guinea pig. The energetic consequences of hypoxia differed according to species and in a different manner from the mechanical parameters. Hypoxia decreased the economy of tension generation in rat heart, in contrast to no change in guinea pig and frog muscle. These results suggest that in terms of mechano-ener- getic properties, cardiac muscles with V1 isomyosin were more sensitive to hypoxia than those containing V3 isomyosin. Key words Cardiac muscle – hypoxia – isomyosin – mechanical efficiency Y. Lecarpentier () INSERM U451-LOA-ENSTA- Ecole Polytechnique 91761 Palaiseau, France E-mail: lecarpen@enstay.ensta.fr T. Joseph · C. Coirault · Y. Lecarpentier Institut National de la Santé et de la Recherche Médicale Unité 451 Laboratoire d’Optique Appliquée Ecole Nationale Supérieure de Techniques Avancées 91761 Palaiseau Service de Physiologie Cardio-Respiratoire Hˆopital Bicˆ etre Centre Hospitalier Universitaire Paris XI Assistance Publique des Hˆ opitaux de Paris 94275 Le Kremlin-Bicˆ etre, France Received: 8 October 1999 Returned for revision: 3 November 1999 Revision received: 28 January 2000 Accepted: 23 February 2000 BRC 212 Introduction Myocardial hypoxia is associated with various major cellular ionic and metabolic changes, in particular a decrease in high- energy phosphate content (1, 2), which lead to mechanical impairment (2, 13, 20, 22, 29, 32). These findings have been studied in several in vitro models (14, 19) but myocardial intrinsic energetic consequences of hypoxia have not yet been well documented. The aim of the present study was therefore to determine the mechanical and intrinsic energetic changes induced by hypoxia in the isolated cardiac muscles of differ- ent species characterized by different isomyosin patterns. Experiments were performed on two mammalian species (rat and guinea pig) and one amphibian (frog). The isomyosin pattern is predominantly V1 with high ATPase activity in the rat (8, 18, 25) and V3 with low ATPase activity in the guinea pig and frog (8, 25). Classic parameters of contraction and derived energetic parameters were determined at baseline and after hypoxia. Energetic parameters were derived from the hyperbolic tension-velocity relationship (9, 17, 22, 34). The characteristics of the hyperbola (i.e., the G curvature of the tension-velocity relationship) have been shown to correlate with the myothermal economy of tension generation (3, 17, 23, 34, 35) and isomyosin pattern (3, 23).