In vitro activity: Blebbistatin, inhibits cytokinesis, alters the smooth movement of fish keratocytes and inhibits the spontaneous blebbing of a cell line lacking filamin. Blebbistatin is shown to inhibit the enzymatic activities of HMM fragments of nonmuscle myosin IIA, nonmuscle myosin IIB and of rabbit skeletal muscle myosin S1, but not smooth muscle myosin blebbistatin rapidly and reversibly inhibits Mg-ATPase activity and in vitro motility of non-muscle myosin IIA and IIB for several species, while poorly inhibiting smooth muscle myosin (IC50 = 80 μM). Blebbistatin potently inhibits Dictyostelium myosin II, but poorly inhibits Acanthamoeba myosin II. Blebbistatin does not inhibit representative myosin superfamily members from classes I, V, and X. Blebbistatin does not compete with nucleotide binding to the skeletal muscle myosin subfragment-1. The inhibitor preferentially binds to the ATPase intermediate with ADP and phosphate bound at the active site, and it slows down phosphate release. Blebbistatin interferes neither with binding of myosin to actin nor with ATP-induced actomyosin dissociation. Instead, it blocks the myosin heads in a products complex with low actin affinity.

Kinase Assay: Actin-activated MgATPase activity is measured using an NADH-coupled assay in a Beckman DU 640 spectrophotometer. Blebbistatin [a racemic mixture of the (+) and (-) enantiomers] is added from stocks dissolved in DMSO and the DMSO concentration is maintained at a constant concentration of 5% in all samples.

Cell Assay: Blebbistatin effectively inhibited actin-myosin interaction in mouse cardiac muscle through a mechanism independent on Ca2+ influx and activation systems. In addition, blebbistatin prevented thrombin-mediated inhibition of intercellular calcium wave propagation in bovine corneal endothelial cells.

Science. 2003 Mar 14;299(5613):1743-7; J Muscle Res Cell Motil. 2004;25(4-5):337-41.