Alterations in expression of myosin and myosin light chain kinases in response to vascular injury

Histochemical analysis of balloon-injured rat carotid arteries revealed a c oordinated expression of nonmuscle myosin heavy chain-A and -B (NM-A and NM -B) in response to injury. Expression of these nonmuscle myosin forms shift s from the media to the adventitia and intima. In contrast, expression of s mooth muscle myosin heavy chain-1 (SM-1) within the media is not altered, w hereas smooth muscle myosin heavy chain-2 (SM-2) expression declines. Weste rn blotting shows a statistically significant increase in expression of NM- A that occurs within 6 h in response to carotid injury, suggesting this myo sin form may be an appropriate experimental marker for proliferating, migra ting cells in injured vessels. No overall change in the relative expression level of NM-B was detected, suggesting that compensatory declines in media expression are balanced by increases in the intima and adventitia. Express ion of SM-1 did not change in response to injury, whereas the expression of SM-2 significantly declined between 24 h and 7 days. Expression of myosin light chain kinase is also negatively regulated, and the decline in its exp ression parallels downregulation of SM-2.