Circulating alpha-actin in angina pectoris.

We used Western blot, a highly sensitive technique that detects amounts of protein as low as 0.1 to 1.0 ng, to investigate the possible presence in the blood stream of the contractile protein alpha-actin in 29 patients diagnosed with angina pectoris (Braunwald's classification). Circulating protein was identified with a monoclonal antibody specific for cardiac alpha-actin. Of the 20 control samples of blood, the immunoblot results were negative for alpha-actin in 19. Of the 30 patients with skeletal muscle damage caused by surgery, 27 were negative for circulating alpha-actin. Of the 29 patients with angina pectoris, circulating alpha-actin was found in 19 as a 43 kDa band in immunoblots. Of the four patients with anterior acute myocardial infarction, mean concentration of circulating alpha-actin was 58 mg/l. Among the patients with angina pectoris, the highest circulating concentrations (mean 40 mg/l) was found in those with prolonged angina (class III B, according to Braunwald's classification). In the entire group of individuals with angina pectoris alpha-actin was detectable in serum for up to 175 h after the onset of pain, and showed two peaks, one at 1 h (112 mg/l) and one at 50 h (82 mg/l) after the onset of pain. These findings reinforce the notion that unstable angina should be considered a serious condition.