Biphasic alterations in coronary smooth muscle Ca2+ regulation in a repeat cross-sectional study of coronary artery disease severity in metabolic syndrome

- Coronary artery disease (CAD) progresses around the circumference of the artery, followed by encroachment on the lumen.
- SERCA activity is increased in early, mild CAD and decreased in late, severe CAD.
- Voltage-gated Ca2+ channel (VGCC) function is increased in early, mild CAD.
- Increased SERCA and VGCC function are associated with elevated proliferation in early, mild CAD.

Background and aimsCoronary artery disease (CAD) is progressive, classified by stages of severity. Alterations in Ca2+ regulation within coronary smooth muscle (CSM) cells in metabolic syndrome (MetS) have been observed, but there is a lack of data in relatively early (mild) and late (severe) stages of CAD. The current study examined alterations in CSM Ca2+ regulation at several time points during CAD progression.MethodsMetS was induced by feeding an excess calorie atherogenic diet for 6, 9, or 12 months and compared to age-matched lean controls. CAD was measured with intravascular ultrasound (IVUS). Intracellular Ca2+ was assessed with fura-2.ResultsIVUS revealed that the extent of atherosclerotic CAD correlated with the duration on atherogenic diet. Fura-2 imaging of intracellular Ca2+ in CSM cells revealed heightened Ca2+ signaling at 9 months on diet, compared to 6 and 12 months, and to age-matched lean controls. Isolated coronary artery rings from swine fed for 9 months followed the same pattern, developing greater tension to depolarization, compared to 6 and 12 months (6 months = 1.8 ± 0.6 g, 9 months = 5.0 ± 1.0 g, 12 months = 0.7 ± 0.1 g). CSM in severe atherosclerotic plaques showed dampened Ca2+ regulation and decreased proliferation compared to CSM from the wall.ConclusionsThese CSM Ca2+ regulation data from several time points in CAD progression and severity help to resolve the controversy regarding up-vs. down-regulation of CSM Ca2+ regulation in previous reports. These data are consistent with the hypothesis that alterations in sarcoplasmic reticulum Ca2+ contribute to progression of atherosclerotic CAD in MetS.