In the present study, the underlying mechanisms for diabetic functional derangement and insulin effect on diabetic cardiomyopathy were investigated with respect to sarcoplasmic reticulum (SR) Ca2⁢-ATPase and phospholamban at the transcriptional and translational levels. The maximal Ca2⁢ uptake and the affinity of Ca2⁢-ATPase for Ca2⁢ were decreased in streptozotocin-induced diabetic rat cardiac SR, however, even minimal amount of insulin could reverse both parameters. Levels of both mRNA and protein of phospholamban were significantly increased in diabetic rat hearts, whereas the mRNA and protein levels of SR Ca2⁢-ATPase were significantly decreased. In case of phospholamban, insulin treatment reverses these parameters to normal levels. Minimal amount of insulin could reverse the protein levels; however, it could not reverse the mRNA level of SR Ca2⁢-ATPase at all. Thus, the decreased SR Ca2⁢ uptake appear to be largely attributed to the decreased SR Ca2⁢-ATPase level, which is further impaired due to the inhibition by the increased level of phospholamban. These results indicate that insulin is involved in the control of intracellular Ca2⁢ in the cardiomyocyte through multiple target proteins via multiple mechanisms for the decrease in the mRNA for both SR Ca2⁢-ATPase and phospholamban which are unknown and needs further study.