Smooth muscle myosin phosphatase inhibition and force enhancement by black sponge toxin

Smooth muscle contraction depends on the state of myosin phosphorylation and hence on the balance of myosin light chain kinase and phosphatase activity. Effects of okadaic acid isolated from black sponge on both enzyme activities and contractility were studied in chemically skinned fibers from guinea pig taenia coli. The toxin strongly inhibits myosin phosphatase and enhances tension development.