Increased calcium buffering in coronary smooth muscle cells from diabetic dyslipidemic pigs

No studies exist concerning the ability of the plasma membrane Ca²⁺ pump (PMCA), sarcoplasmic reticulum Ca²⁺ pump (SERCA) and Na⁺-Ca²⁺ exchanger (NCX) to regulate myoplasmic Ca²⁺ (Ca_m) in vascular smooth muscle cells from diabetic individuals with dyslipidemia. We tested the hypothesis that diabetic dyslipidemia would increase vascular smooth muscle cells to buffer Ca_m. Cells were isolated from the coronary artery of male Yucatan pigs treated for 20 weeks with: (1) a low fat diet (control group); (2) a high fat/cholesterol diet (F group); or (3) alloxan-induced diabetic pigs fed the high fat diet (DF group). The maximum Ca_m response to a depolarizing 80 mM KCl (80 K) solution was evaluated in the absence and presence of thapsigargin (TSG; inhibits SERCA) and low Na (inhibits NCX). In response to 80 K alone, there was no difference in the Ca_m response between groups. In the presence of TSG, the 80 K response decreased by 43% in the DF group; TSG did not affect the 80 K response in the control and F groups. When exposed to both TSG and low Na, the 80 K response also decreased by 55% in the DF group. This suggests increased Ca_m buffering by the PMCA and/or mitochondria in the DF group when SERCA and NCX are inhibited. Compared to the control and F groups, low Na alone elicited a 50% lower Ca_m amplitude in the DF group, which was reversed with TSG treatment; this suggests that SERCA activity is increased in DF pigs. Western blots also indicated a 7-fold increase in the ≃115 kDa band density of an anti-SERCA2 antibody in DF compared to control pigs. This is the first report to demonstrate increased Ca²⁺ buffering, specifically by SERCA, in vascular smooth muscle cells from diabetic individuals with dyslipidemia.