ENERGETICS OF IONIC MOVEMENTS IN HEART-MU SCLE CONTRACTION - PHYSIOLOGICAL AND PATHOLOGICAL ASPECTS

It is widely accepted that the ionic movement across the different mem brane systems (i.e. sarcolemma, sarcoplasmic reticulum, mitochondria), plays a major role on heart muscle metabolism. On the other hand, nei ther the relative role nor the associated energy expenditure of those mechanisms have been definitively established. Biochemical and biophys ical measurements of the different ion exchange mechanisms, have provi ded data leading to the postulation of different models for both resti ng and active metabolism of the heart muscle. The present work analyze s, from an energetic standpoint, available biochemical and biophysical data from the literature calculating the range of energy expenditure that should be attributable to each mechanism. Sodium, potassium and c alcium movements during either resting and/or active state are particu lary analyzed and the fractional role of various organelles (sarcolemm a, sarcoplasmic reticulum and mitochondria) discussed. From this analy sis and the known amount of energy released (or the amount of oxygen c onsumed) by the muscle it is possible to determine whether there is en ough energy for a given model of ionic exchange during the excitation contraction process. In addition to this analysis a comparatively shor t review of energetic studies performed under pathological conditions is also presented. In particular, the pathological conditions analyzed are those with an energetic compromise such as heart hypertrophy, isc hemia and anoxia in which the alteration of ionic transport mechanisms seems to be playing a major role.