Method for assaying compounds affecting smooth muscle contractile state

A method of assaying whether a test compound affects the contractile state of smooth muscle cells, said method comprising:

• (a) providing a system comprising
• (i) cyclic GMP-dependent protein kinase or a fragment thereof, and
• (ii) a myosin phosphatase myosin-binding subunit or a fragment thereof, under conditions in which said kinase can interact with said subunit;
• (b) contacting said test compound with said system;
• and
• (c) determining whether said test compound affects the interaction between said kinase and said subunit as an indication of the ability of said test compound to affect the contractile state of smooth muscle cells.