Inhibition of myosin light-chain kinase activity in the organ of Corti by 0.3-5 kilodalton substances of the otosclerotic perilymph.

The guinea pig organ of Corti contains myosin light-chain kinase (MLCK) activity. The upper and lower most parts of the cochlea do not show significantly different activities of the enzyme, which is Ca2+ and calmodulin-dependent. Short-term noise exposure does not cause a significant change. 0.3-5 Kilodalton substances of the otosclerotic perilymph, separated by SG-25 column chromatography, inhibit the MLCK activity in in vitro organ of Corti preparations. This inhibitory action of the perilymph substances can also be observed with the purified MLCK of turkey gizzard. The activity of the enzyme can be specifically inhibited by cyclic AMP-dependent protein kinase.