Fig. 4. DNA fragmentation in myocytes as assessed by laddering. Total genomic DNA was isolated, labeled with [32P]dCTP, and size-fractionated by electrophoresis. For the various groups, the intensity of the signals corresponding to low-molecular-weight DNA is expressed as percent increase in absorption compared with control (CTL). Norepinephrine (NE)-induced increase in DNA fragmentation is similarly blocked by treatment with diltiazem (DIL; 1 μm), propranolol (PRO; 2 μm), isoflurane (ISO; 1.6 MAC), and halothane (HAL; 1.2 MAC). Data are mean ± SD. *P < 0.0001 versus CTL, †not significant versus CTL. M indicates 1-kb marker.