Identification of myosin isoenzymes in rat cardiac muscle after long-term methamphetamine administration.

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We have reported that long-term administration of methamphetamine (MA) of which main pharmacologic reaction is releasing catecholamine from nerve endings induces rat cardiac lesions such as hypertrophy, myolysis, contraction band necrosis and disarray of myofibers. To further investigate the mechanism of MA induced cardiac injury we examined the myosin isozyme pattern and the actomyosin ATPase activity of the heart. The histological examination of r-at heart administered MA 1 mg/kg b. w. /day for 8 weeks and 12 weeks revealed hypertrophy, atrophy, myolysis and disarray of myofibers. Isozyme patterns of myosin were investigated by polyacrylamide gel electrophoresis in the presence of pyrophosphate as described by Hoh et al. and were estimated by densitometry. Though there was a significant difference between VI value of controls which were injected saline same volume for 8 w and 12 w (69.3 +- 8.0 % vs 56.2 +- 5.7 %, respectively), no significant difference was observed between controls and MA treated rat hearts in both groups. Mg^2-ATPase activity in the presence of 10 or 0.1muM Ca^<2+> were measured by previously reported method. In result, there were no significant differences in Mg^<2+>-ATPase activity at 10muM Ca^<2+> between 8 w and 12 w controls and each MA treated rats, but there was a significant increase of Mg^<2+>-ATPase activity at 0.1muM Ca^<2+> in 12 w HA treated rats compared with controls. The result suggest that there may be some changes in cardiac function after long-term MA administration as well as histologic changes.