Affiliation:
1. From the Laboratories of Experimental Cardiology (G.A., K.R.S.) and Physiology (M.V.H., L.R., P.V., F.W.), University of Leuven, Belgium.
Abstract
SERCA2a is the cardiac-specific isoform of Ca
2+
-ATPase of the sarcoplasmic reticulum (SR). A reduction of SERCA2a has been implicated in the contractile dysfunction of heart failure, and partial knockout of the SERCA2 gene (
Atp2a2
+/−
mice) reiterated many of the features of heart failure. Yet, mice with a mutation of
Atp2a2
, resulting in full suppression of the SERCA2a isoform and expression of the SERCA2b isoform only (
SERCA2
b/b
), showed only moderate functional impairment, despite a reduction by 40% of the SERCA2 protein levels. We examined in more detail the Ca
2+
handling in isolated cardiac myocytes from
SERCA2
b/b
. At 0.25 Hz stimulation, the amplitude of the [Ca
2+
]
i
transients, SR Ca
2+
content, diastolic [Ca
2+
]
i
, and density of
I
CaL
were comparable between WT and
SERCA2
b/b
. However, the decline of [Ca
2+
]
i
was slower (t
1/2
154±7 versus 131±5 ms;
P
<0.05). Reducing the amplitude of the [Ca
2+
]
i
transient (eg, SR depletion), removed the differences in [Ca
2+
]
i
decline. In contrast, increasing the Ca
2+
load revealed pronounced reduction of SR Ca
2+
uptake at high [Ca
2+
]
i
. There was no increase in Na
+
-Ca
2+
exchange protein or function. Theoretical modeling indicated that in the
SERCA2
b/b
mouse, the higher Ca
2+
affinity of SERCA2b partially compensates for the 40% reduction of SERCA expression. The lack of SR depletion in the
SERCA2
b/b
may also be related to the absence of upregulation of Na
+
-Ca
2+
exchange. We conclude that for SERCA isoforms with increased affinity for Ca
2+
, a reduced expression level is better tolerated as Ca
2+
uptake and storage are impaired only at higher Ca
2+
loads.
Publisher
Ovid Technologies (Wolters Kluwer Health)
Subject
Cardiology and Cardiovascular Medicine,Physiology
Cited by
24 articles.
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