The Effect of Trans-Cinnamaldehyde on Na,K-ATPase Activity in Rabbit Nonpigmented Ciliary Epithelium

Abstract

The ciliary epithelium (CE), the tissue responsible for aqueous humor (AH) production, is the outer layer of the ciliary process and is composed of the pigmented epithelium (PE) and the nonpigmented epithelium (NPE). Previous studies have shown that inhibition of Na,K-ATPase in the CE by ouabain causes a 62% decrease in AH formation and that there is more Na,K-ATPase in the NPE than in the PE. In addition, cinnamaldehyde (CA) has been shown to inhibit Na,KATPase and other ATPases in different tissues and organisms, such as rat hepatocyte and certain bacteria. The purpose of this study was to determine if trans-CA inhibits Na,K-ATPase in rabbit NPE (rNPE). Na,K-ATPase activity was measured using a colorimetric method quantifying the amount of ATP hydrolyzed. Rb⁺ which is transported by Na,K-ATPase in a way similar to K⁺, was measured through atomic absorption spectrophotometry. The present study indicates that trans-CA has a linear concentration-dependent inhibitory effect on Na,K-ATPase and non-Na,K-ATPase activity in rNPE at concentrations of 25 and 50 μM. Trans-CA may be used as a compound to inhibit Na,K-ATPase in the CE in order to decrease aqueous humor production and intraocular pressure.