Altered SR protein expression associated with contractile dysfunction in diabetic rat hearts

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Abstract
The goal of this study was to examine whether alteration of sarcoplasmic reticulum (SR) protein levels is associated with early-onset diastolic and late-onset systolic dysfunction in streptozotocin (STZ)-induced diabetic rat hearts. Four-week diabetic rat hearts exhibited slow relaxation, whereas 6-wk diabetic rat hearts exhibited slow and depressed contraction. Total phospholamban level was increased, and phosphorylated level was decreased in 4- and 6-wk diabetic rat hearts. Sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA2) protein level was unchanged in 4-wk but decreased in 6-wk diabetic rat hearts. Only the apparent affinity of SR Ca2+uptake for Ca2+was decreased in 4-wk diabetic rat hearts, but the apparent affinity and the maximum rate was decreased in 6-wk diabetic rat hearts. Insulin treatment of the diabetic rats normalized SR protein expression and function. It was concluded that an increase in nonphosphorylated phospholamban and a decrease in the apparent affinity of SR Ca2+pump for Ca2+are associated with early-onset diastolic dysfunction and decreases in SERCA2 protein level and apparent affinity and maximum velocity of SR Ca2+pump are associated with late-onset systolic dysfunction in diabetic rats.