Subpopulations of human heart mitochondria

Anatomically and biochemically distinct populations of cardiac mitochondria have been isolated from a number of animal species. The physiologic differences between subsarcolemmal (SS) and interfibrillar (IF) mitochondria, coupled with their different location within the cytomatrix, have led to speculation about possible specificities of function within the myocardial cell. To date, these two mitochondrial subpopulations have not been demonstrated in human cardiac tissue. Subsarcolemmal and interfibrillar cardiac mitochondria were isolated from papillary muscle removed from five patients undergoing mitral valve replacement surgery. Mitochondrial respiratory activity was determined polarographically. IF mitochondria had significantly higher state 3 (ADP-dependent) rates of respiration then SS mitochondria (116.7 ± 7.1 versus 86.5 ± 8.3 ng atoms or oxygen per minute per milligram mitochondrial protein; P < 0.05 [mean ± SE]). These data agree with similar studies performed in other animal species and support the concept of distinct subpopulations of mitochondria within the human myocardial cell.