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CaATPase content is lower in cardiac sarcoplasmic reticulum isolated from old rats
1Department of Medicine, Baylor College of Medicine 77030-3498.
Insights
Cardiac sarcoplasmic reticulum (SR) from senescent rats shows slower calcium uptake due to reduced calcium adenosinetriphosphatase (CaATPase) protein content. This age-related decline impacts heart function.
Area of Science:
- Cardiovascular Physiology
- Aging Research
- Molecular Biology
Background:
- Cardiac sarcoplasmic reticulum (SR) calcium transport is crucial for heart function.
- Aging is associated with declines in physiological processes, including cardiac function.
- Calcium adenosinetriphosphatase (CaATPase) is the primary pump responsible for SR calcium uptake.
Purpose of the Study:
- To investigate the mechanism behind the reduced calcium uptake rate in cardiac SR from senescent rats.
- To compare CaATPase activity and protein content between adult and senescent rat cardiac SR.
Main Methods:
- Isolation of cardiac sarcoplasmic reticulum (SR) from adult and senescent Fischer 344 male rats.
- Measurement of calcium uptake rates and CaATPase activity.
- Analysis of CaATPase kinetics (Vmax, affinities) and phosphoenzyme formation.
- Quantification of immunoreactive CaATPase protein content using Western blotting.
Main Results:
- Cardiac SR from senescent rats exhibited a 28-44% slower rate of calcium uptake compared to adult rats.
- Maximal velocity (Vmax) of CaATPase activity was 20-30% lower in senescent SR, with unaltered affinities for calcium and ATP.
- Calcium-dependent phosphoenzyme content was decreased in senescent SR, matching the lower Vmax.
- Immunoreactive CaATPase protein content was significantly reduced (22%) in SR from senescent rats.
Conclusions:
- The primary mechanism for slower calcium transport in senescent rat cardiac SR is a reduced content of the CaATPase protein.
- This age-related decrease in CaATPase protein contributes to impaired cardiac calcium handling in older rats.
Abstract:
The rate of oxalate-facilitated ATP-dependent calcium uptake by the calcium pump, calcium adenosinetriphosphatase (CaATPase), is 30-40% slower in the sarcoplasmic reticulum (SR) isolated from the hearts of senescent Fischer 344 male rats. To determine the underlying mechanism, cardiac SR was isolated from 11- to 12-mo-old (adult) and 22- to 24-mo-old (senescent) male Fischer 344 rats. The yield of SR and contamination by other membrane organelles were similar between the groups. The rate of calcium uptake by the homogenate and isolated SR was 28-44% slower (P < 0.05) in the senescent group. In the isolated SR the calculated maximal velocity (Vmax) of CaATPase activity as a function of varying concentrations of ATP or calcium was 20-30% lower (P < 0.05) in the senescent group; however, the affinities for both calcium and ATP of CaATPase activity were unaltered. The lower Vmax was matched by a decreased (P < 0.05) content of calcium-dependent phosphoenzyme (EP) in the SR isolated from the senescent rats. Thus the ratio of enzyme activity to phosphoenzyme content (Vmax/EP) was similar between the groups. The immunoreactive CaATPase protein was 22 +/- 2% lower in the SR from the senescent rats. Taken together the data indicate that the major mechanism underlying the slower calcium transport by cardiac SR isolated from old rats is a lower content of the CaATPase protein.