Phospholamban ‐ SERCA2a Interactions In Hearts From Streptozotocin‐Induced Diabetic Rats

Abstract

Reduced cardiac contractility is a primary cause for morbidity in diabetic patients. One protein that contributes to this defect is the sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA2a). The molecular mechanisms responsible for loss of SERCA2a activity during diabetes remain incompletely understood. We investigated whether the interaction between SERCA2a and its inhibitor protein, phospholamban (PLN) changes during diabetes. Diabetes was induced in male Sprague-Dawley rats using a single dose of streptozotocin (50mg/kg; iv). After 8 weeks, diabetic and aged-matched control rats were sacrificed. Left ventricular tissues were isolated and homogenized. Cardiac membrane vesicles (CMVs) were prepared by differential ultracentrifugation and protein concentrations determined. CMVs were then electrophoresed on non-denaturing polyacrylamide gels and proteins transferred onto PVDF membranes. PLN and SERCA2a were then detected by Western blotting. We found that PLN and SERCA2a co-migrated. In diabetics steady state levels of PLN and SERCA2a were decreased by 47.2 % and 51.0 % respectively and PLN/SERCA2a ratios increased by 10%. However, more PLN remained bound to SERCA2a in diabetic samples than in controls. This suggests that reduced dissociation of PLN from SERCA2a may contribute to reduction in SERCA2a activity in diabetics. Supported by The School for Graduate Studies and Research, U.W.I and the Edna Ittner Research Foundation.