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Calpain activity of hypertrophic hearts from hypertensive rats
M A Cicilini1, M M Resende, N S Bissoli
1Departamento de Ciências Fisiológicas, Universidade Federal do Espírito Santo, Vitória, Brasil.
Insights
Hypertension in rats significantly decreased heart calpain activity, an enzyme crucial for muscle protein turnover, despite causing ventricular hypertrophy. This suggests altered protein degradation in hypertensive heart disease.
Area of Science:
- Biochemistry
- Cardiovascular Physiology
- Molecular Biology
Background:
- Heart tissue possesses Ca(2+)-activated proteinase calpain, essential for muscle protein turnover.
- Ventricular hypertrophy is a common cardiac adaptation in hypertension.
- The role of calpain in hypertensive cardiac remodeling requires further investigation.
Purpose of the Study:
- To quantify calpain-like activity in left ventricular homogenates from hypertensive rats exhibiting ventricular hypertrophy.
- To investigate the relationship between hypertension, ventricular hypertrophy, and calpain activity.
Main Methods:
- Calpain activity was measured using a heat-denatured azocasein substrate assay in rat left ventricle homogenates.
- Calcium-dependent and independent activities were determined using calcium and EGTA, respectively.
- Experimental groups included control, high salt, DOCA-salt induced hypertension, and spontaneously hypertensive rats (SHR).
Main Results:
- Hypertension in DOCA-salt and SHR groups induced significant left ventricular hypertrophy (26% and 54%, respectively).
- Calpain activity decreased by 30% in both hypertensive groups (P < 0.01).
- High salt intake alone decreased calpain activity without inducing hypertrophy.
Conclusions:
- Hypertension is associated with reduced calpain activity in the rat heart, independent of hypertrophy.
- The observed decrease in calpain activity may indicate altered protein degradation pathways in hypertensive heart disease.
- Further research is needed to elucidate the precise role of calpain in cardiac remodeling.
Abstract:
Heart tissue contains large amounts of the Ca(2+)-activated proteinase calpain which has been assigned a specific function in the turnover of muscle protein. The objective of the present study was to determine calpain (E.C. 3.4.22.17)-like activity in homogenates of left ventricle from hypertensive rats that developed ventricular hypertrophy. Calpain activity was assayed using heat-denatured azocasein as a substrate in the presence of 1 mM calcium and corrected by subtraction of the Ca(2+)-independent activities. The latter were measured in the presence of 1 mM EGTA and the products read at 440 nm. Male Wistar rats (225 g) were assigned to control (N = 8, normal drinking water), salt (N = 6, drinking water containing 1% NaCl) and DOCA-salt (N = 6, deoxycorticosterone acetate, 8 mg/kg, sc, twice a week for 20 days plus drinking water containing 1% NaCl) groups. SHR (N = 6, spontaneously hypertensive rats) were also used. The calpain activity of the control group was at 3.90 +/- 0.22 mU/g wet weight tissue. Hypertension induced significant left ventricular hypertrophy in DOCA-salt rats (26%) and in SHR (54%) and a 30% decrease in calpain activity in both groups (P < 0.01). In the high salt load (salt group) calpain activity was also decreased, but this was not accompanied by hypertrophy. In the present indirect measurement of protein degradation capacity of heart tissue homogenates the proteolytic activity was activated (221%) by 1 mM calcium and inhibited (84%) by 1 mM EGTA after a 48-h incubation period, indicating the destruction of the calpain inhibitor.(ABSTRACT TRUNCATED AT 250 WORDS)