Prostaglandin F 2 ␣, but Not Latanoprost, Increases the Ca 2؉ Sensitivity of the Pig Iris Sphincter Muscle

PURPOSE. To determine the mechanisms underlying prostaglandin (PG) F 2 ␣-, carbachol (CCh)-, or latanoprost (a PGF 2 ␣ analogue)-induced contraction of the pig iris sphincter muscle. METHODS. Effects of these agents on myofilament Ca 2ϩ sensitivity were evaluated and compared with the use of receptorcoupled permeabilized preparations by ␣-toxin. The effects of PGF 2 ␣ and CCh on the phosphorylation of myosin light chain (MLC) were also analyzed. RESULTS. In the intact strips, all three of these agents induced contractions. CONCLUSIONS. PGF 2 ␣, but not latanoprost, induced Ca 2ϩ sensitization of the pig iris sphincter muscle in an MLC phosphorylation-dependent manner through the rho-rho kinase pathway. The effect of latanoprost on the Ca 2ϩ sensitization mechanism was different from that of PGF 2 ␣ and was thought to play a beneficial role in glaucoma treatment. (Invest Ophthalmol Vis Sci