The C terminus of cardiac troponin I is essential for full inhibitory activity and Ca2+ sensitivity of rat myofibrils.

Although the C terminus of troponin I is known to be important in myofilament Ca2+ regulation in skeletal muscle, the regulatory function of this region of cardiac troponin I (cTnI) has not been defined. To address this question, the following recombinant proteins were expressed in Escherichia coli and purified: mouse wild-type cTnI (WT cTnI; 211 residues), cTnI-(1-199) (missing 12 residues), cTnI-(1-188) (missing 23 residues), and cTnI-(1-151) (missing 60 residues). The inhibitory activity of cTnI and the mutants was tested in myofibrils, from which cTnI.cTnC was extracted by exchanging endogenous cardiac troponin with exogenous cTnT causing the Ca2+ sensitivity of the myofibrils to be lost. Addition of increasing amounts of exogenous WT cTnI or cTnI-(1-199) to cTnT-treated myofibrils at pCa 8 caused a concentration-dependent inhibition of the maximum ATPase activity. However, cTnI-(1-188) and cTnI-(1-151) inhibited this activity to about 75% and 50% of that of the WT cTnI, respectively. We also formed a complex of either WT cTnI or each of the mutants with cTnC, reconstituted the complex into the cTnT-treated myofibrils, and measured the Mg2+-ATPase activity as a function of pCa. We found that the cTnI-(1-188).cTnC complex only partially restored Ca2+ sensitivity, whereas the cTnI-(1-151).cTnC complex did not restore any Ca2+ sensitivity. Each cTnI C-terminal deletion mutant was able to bind to cTnC, as shown by urea-polyacrylamide gel-shift analysis and size exclusion chromatography. Each mutant also co-sedimented with actin. Our results indicate that residues 152-199 (C-terminal to the inhibitory region) of cTnI are essential for full inhibitory activity and Ca2+ sensitivity of myofibrillar ATPase activity in the heart.

[Clinical observation of wenxin decoction in treating 82 patients with spontaneous angina pectoris].

One hundred twenty-two patients with spontaneous angina pectoris (SAP) were randomly divided into treated group (82 cases) and control group (40 cases), and treated with Wenxin decoction and isosorbide dinitrate respectively. Results showed that in treated group the total effective rate of SAP was 95.12% and that of electrocardiographic findings were 74.39%. These results were all superior to those of control group (P < 0.01). Moreover, results of extracorporeal thrombosis test showed after Wenxin decoction treatment, the length of thrombus decreased from 23.56 +/- 5.47 mm to 20.04 +/- 5.17 mm, the wet weight of it decreased from 92.65 +/- 18.45 mg to 76.94 +/- 15.08 mg and the dry weight from 21.76 +/- 7.30 mg to 16.90 +/- 5.35 mg. The submaximal exercise test revealed an increase of exercise time from 474.66 +/- 96.33 seconds to 548.83 +/- 99.93 seconds, increase of acting quantity from 104.16 +/- 19.65 W to 123.61 +/- 24.96 W and a decrease of ST segment depression from 0.183 +/- 0.041 mV to 0.139 +/- 0.038 mV. These results suggested that Wenxin decoction is valuable in treating SAP.