ML-7, Chelerythrine and Phorbol Ester Increase Outflow Facility in the Monkey Eye

Abstract

Baseline or post-drug outflow facility was measured by two-level constant pressure perfusion of the anterior chamber (AC). The AC of one eye of cynomolgus monkeys was exchanged with the myosin light chain kinase (MLCK) inhibitor ML-7, the protein kinase (PK) C inhibitor chelerythrine (CHEL), or the PKC activator phorbol myristate acetate (PMA), followed by continuous AC infusion of the drug. The opposite eye similarly received the corresponding vehicle solution. The facility-effectiveness of subthreshold doses of ML-7 or CHEL+a subthreshold dose of the serine-threonine kinase inhibitor H-7, and of facility-effective doses of CHEL+a subthreshold or effective dose of PMA, were also determined. In 45min post-exchange perfusions, 100 and 500μM ML-7 increased outflow facility by 32 and 76%, while 100 and 500μM CHEL increased facility by 68 and 101%, respectively, adjusted for baseline and contralateral control eye resistance washout. In 90min post-exchange perfusions, 100μM ML-7 or CHEL time-dependently increased outflow facility by 23, 49 and 69%, or by 44, 108 and 125% in the first, second and third 30min periods, respectively. At 50μM, ML-7 was ineffective, but CHEL increased outflow facility by 36% in the third 30min period. Ten μM H-7 potentiated the outflow facility effect of 50μM ML-7 or 20μM CHEL by 36 and 28%, respectively, in the second 30min period, and that of 50μM CHEL by 44% in the overall 60min post-exchange perfusion, compared to the H-7 only-treated contralateral eye. Ten, 50 or 100n M PMA dose-dependently increased outflow facility by 23, 62 or 174%. Ten n M PMA+50μM CHEL did not induce any additional significant changes in outflow facility compared to 50n M CHEL alone, while the effect of 50n M PMA and 100μM CHEL together was 63% more than that of 100μM CHEL alone. In conclusion, ML-7/CHEL may increase outflow facility by a cytoskeletal mechanism. Separate or combined treatment with CHEL and PMA increases outflow facility, suggesting that PKC inhibition may not be involved in the facility-increase with either drug.