Altered expression of high-molecular-weight calmodulin-binding protein in human ischaemic myocardium
✍ Scribed by Kakkar, Rakesh; Radhi, Jasim M.; Rajala, Raju V. S.; Sharma, Rajendra K.
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 375 KB
- Volume
- 191
- Category
- Article
- ISSN
- 0022-3417
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✦ Synopsis
A high-molecular-weight calmodulin-binding protein (HMWCaMBP) was previously identi®ed and puri®ed from the cytosolic fraction of bovine heart. Based on the sequence homology, amino acid analysis, antibody reactivity, and calpain inhibition, HMWCaMBP has been identi®ed as a homologue of the calpain inhibitor calpastatin. In the present study the expression of HMWCaMBP was investigated in normal and ischaemic human myocardium. Western blot analysis of normal human cardiac muscle extract with the polyclonal antibody raised against bovine HMWCaMBP indicated a prominent immunoreactive band with a molecular mass of 140 kD. HMWCaMBP was localized in the cytoplasm and myo®laments of cardiac myocytes. Furthermore, Western blot analysis of normal and ischaemic cardiac tissues indicated a decrease in the expression of HMWCaMBP in ischaemic tissues. These studies were further substantiated by immunohistochemical studies, indicating strong to moderate HMWCaMBP immunoreactivity in normal cardiac muscle and poor to negative immunoreactivity in ischaemic muscle. The results obtained from the rat ischaemic model suggested that the expression of cardiac HMWCaMBP was signi®cantly decreased during ischaemia/reperfusion. In addition, m-calpain and m-calpain expression was higher in ischaemic cardiac tissue samples than in normal controls. The calpain inhibitory activity of ischaemic cardiac tissues was signi®cantly lower than normal cardiac tissue samples. In some cases of cardiac ischaemia, HMWCaMBP highlighted the contraction band necrosis seen at the margins of a myocardial infarct. In vitro, HMWCaMBP was proteolysed by m-calpain and m-calpain. These results indicate that HMWCaMBP could be susceptible to proteolysis by calpains during ischaemia or reperfusion and may play a contributory role in myocardial injury.