A significant dephosphorylation of exogenous phosphorylase a by serine
/threonine protein phosphatases in tissue extracts of rabbit ciliary e
pithelium and iris-ciliary body was observed. Okadaic acid caused a co
ncentration-dependent inhibition of this dephosphorylation. In a serie
s of diluted samples, selective inhibitions of protein phosphatase 2A
by 1 nM okadaic acid and protein phosphatase 1 by 1 mu M okadaic acid
were determined. In the preparation of ciliary epithelium, the ratio o
f protein phosphatase 1 to protein phosphatase 2A activity was estimat
ed to be 1:2. Dephosphorylation by other phosphatases was little. In t
he preparation of iris-ciliary body, the ratio of protein phosphatase
1 to protein phosphatase 2A activity was approximately 2.5:1. Other ph
osphatases were also present.