The actin-binding protein SM22α marks contractile differentiation in smooth muscle, but its function is unknown. We tested its role in arterial contractility and stretch-sensitive vascular protein synthesis. Active stress in depolarised mesenteric resistance arteries and portal veins was reduced by 40% in SM22α−/− mice. Passive and active arterial circumference–force relationships were shifted leftwards, whereas α1-adrenergic responses were increased. Actin contents were 10–25% lower in vessels from SM22α−/− mice, but protein composition was otherwise similar. Synthesis of SM22α, calponin and α-actin, but not β-actin, was sensitive to stretch. Ablation of SM22α did not affect stretch sensitivity of any of these proteins. Thus, SM22α plays a role in contractility, possibly by affecting actin filament organisation.
