OBJECTIVE: This study examines the extent to which the contractile deficit of 
diabetic cardiomyopathy is due to altered Ca(2+) homeostasis.
RESEARCH DESIGN AND METHODS: Measurements of isometric force and intracellular 
calcium ([Ca(2+)](i), using fura-2/AM) were made in left ventricular (LV) 
trabeculae from rats with streptozotocin-induced diabetes and age-matched 
siblings.
RESULTS: At 1.5 mmol/l [Ca(2+)](o), 37 degrees C, and 5-Hz stimulation 
frequency, peak stress was depressed in diabetic rats (10 +/- 1 vs. 17 +/- 2 
mN/mm(2) in controls; P < 0.05) with a slower time to peak stress (77 +/- 3 vs. 
67 +/- 2 ms; P < 0.01) and time to 90% relaxation (76 +/- 7 vs. 56 +/- 3 ms; P < 
0.05). No difference was found between groups for either resting or peak Ca(2+), 
but the Ca(2+) transient was slower in time to peak (39 +/- 2 vs. 34 +/- 1 ms) 
and decay (time constant, 61 +/- 3 vs. 49 +/- 3 ms). Diabetic rats had a longer 
LV action potential (APD(50), 98 +/- 5 vs. 62 +/- 5 ms; P < 0.0001). Western 
blotting showed that diabetic rats had a reduced expression of 
sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA)2a, with no difference in 
expression of the Na(+)/Ca(2+) exchanger. Immunohistochemistry of LV free wall 
showed that type I collagen was increased in diabetic rats (diabetic 7.1 +/- 
0.1%, control 12.7 +/- 0.1%; P < 0.01), and F-actin content reduced (diabetic 
56.9 +/- 0.6%; control 61.7 +/- 0.4%; P < 0.0001) with a disrupted structure.
CONCLUSIONS: We find no evidence to support the idea that altered Ca(2+) 
homeostasis underlies the contractile deficit of diabetic cardiomyopathy. The 
slower action potential and reduced SERCA2a expression can explain the slower 
Ca(2+) transient kinetics in diabetic rats but not the contractile deficit. 
Instead, we suggest that the observed LV remodeling may play a crucial role.